1 \input texinfo @c -*-texinfo-*-
2 @comment %**start of header
5 @settitle GNU tar @value{VERSION}
14 @c 1. Pay attention to @FIXME{}s and @UNREVISED{}s
15 @c 2. Before creating final variant:
16 @c 2.1. Run `make check-options' to make sure all options are properly
18 @c 2.2. Run `make master-menu' (see comment before the master menu).
20 @include rendition.texi
26 @c Put everything in one index (arbitrarily chosen to be the concept index).
35 This manual is for @acronym{GNU} @command{tar} (version
36 @value{VERSION}, @value{UPDATED}), which creates and extracts files
39 Copyright @copyright{} 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001,
40 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
43 Permission is granted to copy, distribute and/or modify this document
44 under the terms of the GNU Free Documentation License, Version 1.1 or
45 any later version published by the Free Software Foundation; with no
46 Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
47 and with the Back-Cover Texts as in (a) below. A copy of the license
48 is included in the section entitled "GNU Free Documentation License".
50 (a) The FSF's Back-Cover Text is: ``You have the freedom to
51 copy and modify this GNU manual. Buying copies from the FSF
52 supports it in developing GNU and promoting software freedom.''
56 @dircategory Archiving
58 * Tar: (tar). Making tape (or disk) archives.
61 @dircategory Individual utilities
63 * tar: (tar)tar invocation. Invoking @GNUTAR{}.
66 @shorttitlepage @acronym{GNU} @command{tar}
69 @title @acronym{GNU} tar: an archiver tool
70 @subtitle @value{RENDITION} @value{VERSION}, @value{UPDATED}
71 @author John Gilmore, Jay Fenlason et al.
74 @vskip 0pt plus 1filll
80 @top @acronym{GNU} tar: an archiver tool
85 @cindex archiving files
87 The first part of this master menu lists the major nodes in this Info
88 document. The rest of the menu lists all the lower level nodes.
91 @c The master menu goes here.
93 @c NOTE: To update it from within Emacs, make sure mastermenu.el is
94 @c loaded and run texinfo-master-menu.
95 @c To update it from the command line, run
106 * Date input formats::
113 * Configuring Help Summary::
114 * Fixing Snapshot Files::
117 * Free Software Needs Free Documentation::
118 * Copying This Manual::
119 * Index of Command Line Options::
123 --- The Detailed Node Listing ---
127 * Book Contents:: What this Book Contains
128 * Definitions:: Some Definitions
129 * What tar Does:: What @command{tar} Does
130 * Naming tar Archives:: How @command{tar} Archives are Named
131 * Authors:: @GNUTAR{} Authors
132 * Reports:: Reporting bugs or suggestions
134 Tutorial Introduction to @command{tar}
137 * stylistic conventions::
138 * basic tar options:: Basic @command{tar} Operations and Options
139 * frequent operations::
140 * Two Frequent Options::
141 * create:: How to Create Archives
142 * list:: How to List Archives
143 * extract:: How to Extract Members from an Archive
146 Two Frequently Used Options
152 How to Create Archives
154 * prepare for examples::
155 * Creating the archive::
164 How to Extract Members from an Archive
166 * extracting archives::
169 * extracting untrusted archives::
175 * using tar options::
185 The Three Option Styles
187 * Long Options:: Long Option Style
188 * Short Options:: Short Option Style
189 * Old Options:: Old Option Style
190 * Mixing:: Mixing Option Styles
192 All @command{tar} Options
194 * Operation Summary::
196 * Short Option Summary::
208 Advanced @GNUTAR{} Operations
217 How to Add Files to Existing Archives: @option{--append}
219 * appending files:: Appending Files to an Archive
226 Options Used by @option{--create}
228 * override:: Overriding File Metadata.
229 * Ignore Failed Read::
231 Options Used by @option{--extract}
233 * Reading:: Options to Help Read Archives
234 * Writing:: Changing How @command{tar} Writes Files
235 * Scarce:: Coping with Scarce Resources
237 Options to Help Read Archives
239 * read full records::
242 Changing How @command{tar} Writes Files
244 * Dealing with Old Files::
245 * Overwrite Old Files::
250 * Data Modification Times::
251 * Setting Access Permissions::
252 * Directory Modification Times and Permissions::
253 * Writing to Standard Output::
254 * Writing to an External Program::
257 Coping with Scarce Resources
262 Performing Backups and Restoring Files
264 * Full Dumps:: Using @command{tar} to Perform Full Dumps
265 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
266 * Backup Levels:: Levels of Backups
267 * Backup Parameters:: Setting Parameters for Backups and Restoration
268 * Scripted Backups:: Using the Backup Scripts
269 * Scripted Restoration:: Using the Restore Script
271 Setting Parameters for Backups and Restoration
273 * General-Purpose Variables::
274 * Magnetic Tape Control::
276 * backup-specs example:: An Example Text of @file{Backup-specs}
278 Choosing Files and Names for @command{tar}
280 * file:: Choosing the Archive's Name
281 * Selecting Archive Members::
282 * files:: Reading Names from a File
283 * exclude:: Excluding Some Files
284 * wildcards:: Wildcards Patterns and Matching
285 * quoting styles:: Ways of Quoting Special Characters in Names
286 * transform:: Modifying File and Member Names
287 * after:: Operating Only on New Files
288 * recurse:: Descending into Directories
289 * one:: Crossing File System Boundaries
291 Reading Names from a File
297 * problems with exclude::
299 Wildcards Patterns and Matching
301 * controlling pattern-matching::
303 Crossing File System Boundaries
305 * directory:: Changing Directory
306 * absolute:: Absolute File Names
310 * General date syntax:: Common rules.
311 * Calendar date items:: 19 Dec 1994.
312 * Time of day items:: 9:20pm.
313 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
314 * Day of week items:: Monday and others.
315 * Relative items in date strings:: next tuesday, 2 years ago.
316 * Pure numbers in date strings:: 19931219, 1440.
317 * Seconds since the Epoch:: @@1078100502.
318 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
319 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
321 Controlling the Archive Format
323 * Compression:: Using Less Space through Compression
324 * Attributes:: Handling File Attributes
325 * Portability:: Making @command{tar} Archives More Portable
326 * cpio:: Comparison of @command{tar} and @command{cpio}
328 Using Less Space through Compression
330 * gzip:: Creating and Reading Compressed Archives
331 * sparse:: Archiving Sparse Files
333 Making @command{tar} Archives More Portable
335 * Portable Names:: Portable Names
336 * dereference:: Symbolic Links
337 * hard links:: Hard Links
338 * old:: Old V7 Archives
339 * ustar:: Ustar Archives
340 * gnu:: GNU and old GNU format archives.
341 * posix:: @acronym{POSIX} archives
342 * Checksumming:: Checksumming Problems
343 * Large or Negative Values:: Large files, negative time stamps, etc.
344 * Other Tars:: How to Extract GNU-Specific Data Using
345 Other @command{tar} Implementations
347 @GNUTAR{} and @acronym{POSIX} @command{tar}
349 * PAX keywords:: Controlling Extended Header Keywords.
351 How to Extract GNU-Specific Data Using Other @command{tar} Implementations
353 * Split Recovery:: Members Split Between Volumes
354 * Sparse Recovery:: Sparse Members
356 Tapes and Other Archive Media
358 * Device:: Device selection and switching
359 * Remote Tape Server::
360 * Common Problems and Solutions::
361 * Blocking:: Blocking
362 * Many:: Many archives on one tape
363 * Using Multiple Tapes:: Using Multiple Tapes
364 * label:: Including a Label in the Archive
370 * Format Variations:: Format Variations
371 * Blocking Factor:: The Blocking Factor of an Archive
373 Many Archives on One Tape
375 * Tape Positioning:: Tape Positions and Tape Marks
376 * mt:: The @command{mt} Utility
380 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
381 * Tape Files:: Tape Files
382 * Tarcat:: Concatenate Volumes into a Single Archive
387 * Standard:: Basic Tar Format
388 * Extensions:: @acronym{GNU} Extensions to the Archive Format
389 * Sparse Formats:: Storing Sparse Files
396 * PAX 0:: PAX Format, Versions 0.0 and 0.1
397 * PAX 1:: PAX Format, Version 1.0
401 * Generate Mode:: File Generation Mode.
402 * Status Mode:: File Status Mode.
403 * Exec Mode:: Synchronous Execution mode.
407 * GNU Free Documentation License:: License for copying this manual
413 @chapter Introduction
416 and manipulates @dfn{archives} which are actually collections of
417 many other files; the program provides users with an organized and
418 systematic method for controlling a large amount of data.
419 The name ``tar'' originally came from the phrase ``Tape ARchive'', but
420 archives need not (and these days, typically do not) reside on tapes.
423 * Book Contents:: What this Book Contains
424 * Definitions:: Some Definitions
425 * What tar Does:: What @command{tar} Does
426 * Naming tar Archives:: How @command{tar} Archives are Named
427 * Authors:: @GNUTAR{} Authors
428 * Reports:: Reporting bugs or suggestions
432 @section What this Book Contains
434 The first part of this chapter introduces you to various terms that will
435 recur throughout the book. It also tells you who has worked on @GNUTAR{}
436 and its documentation, and where you should send bug reports
439 The second chapter is a tutorial (@pxref{Tutorial}) which provides a
440 gentle introduction for people who are new to using @command{tar}. It is
441 meant to be self contained, not requiring any reading from subsequent
442 chapters to make sense. It moves from topic to topic in a logical,
443 progressive order, building on information already explained.
445 Although the tutorial is paced and structured to allow beginners to
446 learn how to use @command{tar}, it is not intended solely for beginners.
447 The tutorial explains how to use the three most frequently used
448 operations (@samp{create}, @samp{list}, and @samp{extract}) as well as
449 two frequently used options (@samp{file} and @samp{verbose}). The other
450 chapters do not refer to the tutorial frequently; however, if a section
451 discusses something which is a complex variant of a basic concept, there
452 may be a cross reference to that basic concept. (The entire book,
453 including the tutorial, assumes that the reader understands some basic
454 concepts of using a Unix-type operating system; @pxref{Tutorial}.)
456 The third chapter presents the remaining five operations, and
457 information about using @command{tar} options and option syntax.
459 The other chapters are meant to be used as a reference. Each chapter
460 presents everything that needs to be said about a specific topic.
462 One of the chapters (@pxref{Date input formats}) exists in its
463 entirety in other @acronym{GNU} manuals, and is mostly self-contained.
464 In addition, one section of this manual (@pxref{Standard}) contains a
465 big quote which is taken directly from @command{tar} sources.
467 In general, we give both long and short (abbreviated) option names
468 at least once in each section where the relevant option is covered, so
469 that novice readers will become familiar with both styles. (A few
470 options have no short versions, and the relevant sections will
474 @section Some Definitions
478 The @command{tar} program is used to create and manipulate @command{tar}
479 archives. An @dfn{archive} is a single file which contains the contents
480 of many files, while still identifying the names of the files, their
481 owner(s), and so forth. (In addition, archives record access
482 permissions, user and group, size in bytes, and data modification time.
483 Some archives also record the file names in each archived directory, as
484 well as other file and directory information.) You can use @command{tar}
485 to @dfn{create} a new archive in a specified directory.
488 @cindex archive member
491 The files inside an archive are called @dfn{members}. Within this
492 manual, we use the term @dfn{file} to refer only to files accessible in
493 the normal ways (by @command{ls}, @command{cat}, and so forth), and the term
494 @dfn{member} to refer only to the members of an archive. Similarly, a
495 @dfn{file name} is the name of a file, as it resides in the file system,
496 and a @dfn{member name} is the name of an archive member within the
501 The term @dfn{extraction} refers to the process of copying an archive
502 member (or multiple members) into a file in the file system. Extracting
503 all the members of an archive is often called @dfn{extracting the
504 archive}. The term @dfn{unpack} can also be used to refer to the
505 extraction of many or all the members of an archive. Extracting an
506 archive does not destroy the archive's structure, just as creating an
507 archive does not destroy the copies of the files that exist outside of
508 the archive. You may also @dfn{list} the members in a given archive
509 (this is often thought of as ``printing'' them to the standard output,
510 or the command line), or @dfn{append} members to a pre-existing archive.
511 All of these operations can be performed using @command{tar}.
514 @section What @command{tar} Does
517 The @command{tar} program provides the ability to create @command{tar}
518 archives, as well as various other kinds of manipulation. For example,
519 you can use @command{tar} on previously created archives to extract files,
520 to store additional files, or to update or list files which were already
523 Initially, @command{tar} archives were used to store files conveniently on
524 magnetic tape. The name @command{tar} comes from this use; it stands for
525 @code{t}ape @code{ar}chiver. Despite the utility's name, @command{tar} can
526 direct its output to available devices, files, or other programs (using
527 pipes). @command{tar} may even access remote devices or files (as archives).
529 You can use @command{tar} archives in many ways. We want to stress a few
530 of them: storage, backup, and transportation.
532 @FIXME{the following table entries need a bit of work.}
535 Often, @command{tar} archives are used to store related files for
536 convenient file transfer over a network. For example, the
537 @acronym{GNU} Project distributes its software bundled into
538 @command{tar} archives, so that all the files relating to a particular
539 program (or set of related programs) can be transferred as a single
542 A magnetic tape can store several files in sequence. However, the tape
543 has no names for these files; it only knows their relative position on
544 the tape. One way to store several files on one tape and retain their
545 names is by creating a @command{tar} archive. Even when the basic transfer
546 mechanism can keep track of names, as FTP can, the nuisance of handling
547 multiple files, directories, and multiple links makes @command{tar}
550 Archive files are also used for long-term storage. You can think of
551 this as transportation from the present into the future. (It is a
552 science-fiction idiom that you can move through time as well as in
553 space; the idea here is that @command{tar} can be used to move archives in
554 all dimensions, even time!)
557 Because the archive created by @command{tar} is capable of preserving
558 file information and directory structure, @command{tar} is commonly
559 used for performing full and incremental backups of disks. A backup
560 puts a collection of files (possibly pertaining to many users and
561 projects) together on a disk or a tape. This guards against
562 accidental destruction of the information in those files.
563 @GNUTAR{} has special features that allow it to be
564 used to make incremental and full dumps of all the files in a
568 You can create an archive on one system, transfer it to another system,
569 and extract the contents there. This allows you to transport a group of
570 files from one system to another.
573 @node Naming tar Archives
574 @section How @command{tar} Archives are Named
576 Conventionally, @command{tar} archives are given names ending with
577 @samp{.tar}. This is not necessary for @command{tar} to operate properly,
578 but this manual follows that convention in order to accustom readers to
579 it and to make examples more clear.
584 Often, people refer to @command{tar} archives as ``@command{tar} files,'' and
585 archive members as ``files'' or ``entries''. For people familiar with
586 the operation of @command{tar}, this causes no difficulty. However, in
587 this manual, we consistently refer to ``archives'' and ``archive
588 members'' to make learning to use @command{tar} easier for novice users.
591 @section @GNUTAR{} Authors
593 @GNUTAR{} was originally written by John Gilmore,
594 and modified by many people. The @acronym{GNU} enhancements were
595 written by Jay Fenlason, then Joy Kendall, and the whole package has
596 been further maintained by Thomas Bushnell, n/BSG, Fran@,{c}ois
597 Pinard, Paul Eggert, and finally Sergey Poznyakoff with the help of
598 numerous and kind users.
600 We wish to stress that @command{tar} is a collective work, and owes much to
601 all those people who reported problems, offered solutions and other
602 insights, or shared their thoughts and suggestions. An impressive, yet
603 partial list of those contributors can be found in the @file{THANKS}
604 file from the @GNUTAR{} distribution.
606 @FIXME{i want all of these names mentioned, Absolutely. BUT, i'm not
607 sure i want to spell out the history in this detail, at least not for
608 the printed book. i'm just not sure it needs to be said this way.
609 i'll think about it.}
611 @FIXME{History is more important, and surely more interesting, than
612 actual names. Quoting names without history would be meaningless. FP}
614 Jay Fenlason put together a draft of a @GNUTAR{}
615 manual, borrowing notes from the original man page from John Gilmore.
616 This was withdrawn in version 1.11. Thomas Bushnell, n/BSG and Amy
617 Gorin worked on a tutorial and manual for @GNUTAR{}.
618 Fran@,{c}ois Pinard put version 1.11.8 of the manual together by
619 taking information from all these sources and merging them. Melissa
620 Weisshaus finally edited and redesigned the book to create version
621 1.12. The book for versions from 1.14 up to @value{VERSION} were edited
622 by the current maintainer, Sergey Poznyakoff.
624 For version 1.12, Daniel Hagerty contributed a great deal of technical
625 consulting. In particular, he is the primary author of @ref{Backups}.
627 In July, 2003 @GNUTAR{} was put on CVS at savannah.gnu.org
628 (see @url{http://savannah.gnu.org/projects/tar}), and
629 active development and maintenance work has started
630 again. Currently @GNUTAR{} is being maintained by Paul Eggert, Sergey
631 Poznyakoff and Jeff Bailey.
633 Support for @acronym{POSIX} archives was added by Sergey Poznyakoff.
636 @section Reporting bugs or suggestions
639 @cindex reporting bugs
640 If you find problems or have suggestions about this program or manual,
641 please report them to @file{bug-tar@@gnu.org}.
643 When reporting a bug, please be sure to include as much detail as
644 possible, in order to reproduce it. @FIXME{Be more specific, I'd
645 like to make this node as detailed as 'Bug reporting' node in Emacs
649 @chapter Tutorial Introduction to @command{tar}
651 This chapter guides you through some basic examples of three @command{tar}
652 operations: @option{--create}, @option{--list}, and @option{--extract}. If
653 you already know how to use some other version of @command{tar}, then you
654 may not need to read this chapter. This chapter omits most complicated
655 details about how @command{tar} works.
659 * stylistic conventions::
660 * basic tar options:: Basic @command{tar} Operations and Options
661 * frequent operations::
662 * Two Frequent Options::
663 * create:: How to Create Archives
664 * list:: How to List Archives
665 * extract:: How to Extract Members from an Archive
670 @section Assumptions this Tutorial Makes
672 This chapter is paced to allow beginners to learn about @command{tar}
673 slowly. At the same time, we will try to cover all the basic aspects of
674 these three operations. In order to accomplish both of these tasks, we
675 have made certain assumptions about your knowledge before reading this
676 manual, and the hardware you will be using:
680 Before you start to work through this tutorial, you should understand
681 what the terms ``archive'' and ``archive member'' mean
682 (@pxref{Definitions}). In addition, you should understand something
683 about how Unix-type operating systems work, and you should know how to
684 use some basic utilities. For example, you should know how to create,
685 list, copy, rename, edit, and delete files and directories; how to
686 change between directories; and how to figure out where you are in the
687 file system. You should have some basic understanding of directory
688 structure and how files are named according to which directory they are
689 in. You should understand concepts such as standard output and standard
690 input, what various definitions of the term @samp{argument} mean, and the
691 differences between relative and absolute file names. @FIXME{and what
695 This manual assumes that you are working from your own home directory
696 (unless we state otherwise). In this tutorial, you will create a
697 directory to practice @command{tar} commands in. When we show file names,
698 we will assume that those names are relative to your home directory.
699 For example, my home directory is @file{/home/fsf/melissa}. All of
700 my examples are in a subdirectory of the directory named by that file
701 name; the subdirectory is called @file{practice}.
704 In general, we show examples of archives which exist on (or can be
705 written to, or worked with from) a directory on a hard disk. In most
706 cases, you could write those archives to, or work with them on any other
707 device, such as a tape drive. However, some of the later examples in
708 the tutorial and next chapter will not work on tape drives.
709 Additionally, working with tapes is much more complicated than working
710 with hard disks. For these reasons, the tutorial does not cover working
711 with tape drives. @xref{Media}, for complete information on using
712 @command{tar} archives with tape drives.
714 @FIXME{this is a cop out. need to add some simple tape drive info.}
717 @node stylistic conventions
718 @section Stylistic Conventions
720 In the examples, @samp{$} represents a typical shell prompt. It
721 precedes lines you should type; to make this more clear, those lines are
722 shown in @kbd{this font}, as opposed to lines which represent the
723 computer's response; those lines are shown in @code{this font}, or
724 sometimes @samp{like this}.
726 @c When we have lines which are too long to be
727 @c displayed in any other way, we will show them like this:
729 @node basic tar options
730 @section Basic @command{tar} Operations and Options
732 @command{tar} can take a wide variety of arguments which specify and define
733 the actions it will have on the particular set of files or the archive.
734 The main types of arguments to @command{tar} fall into one of two classes:
735 operations, and options.
737 Some arguments fall into a class called @dfn{operations}; exactly one of
738 these is both allowed and required for any instance of using @command{tar};
739 you may @emph{not} specify more than one. People sometimes speak of
740 @dfn{operating modes}. You are in a particular operating mode when you
741 have specified the operation which specifies it; there are eight
742 operations in total, and thus there are eight operating modes.
744 The other arguments fall into the class known as @dfn{options}. You are
745 not required to specify any options, and you are allowed to specify more
746 than one at a time (depending on the way you are using @command{tar} at
747 that time). Some options are used so frequently, and are so useful for
748 helping you type commands more carefully that they are effectively
749 ``required''. We will discuss them in this chapter.
751 You can write most of the @command{tar} operations and options in any
752 of three forms: long (mnemonic) form, short form, and old style. Some
753 of the operations and options have no short or ``old'' forms; however,
754 the operations and options which we will cover in this tutorial have
755 corresponding abbreviations. We will indicate those abbreviations
756 appropriately to get you used to seeing them. (Note that the ``old
757 style'' option forms exist in @GNUTAR{} for compatibility with Unix
758 @command{tar}. In this book we present a full discussion of this way
759 of writing options and operations (@pxref{Old Options}), and we discuss
760 the other two styles of writing options (@xref{Long Options}, and
761 @pxref{Short Options}).
763 In the examples and in the text of this tutorial, we usually use the
764 long forms of operations and options; but the ``short'' forms produce
765 the same result and can make typing long @command{tar} commands easier.
766 For example, instead of typing
769 @kbd{tar --create --verbose --file=afiles.tar apple angst aspic}
775 @kbd{tar -c -v -f afiles.tar apple angst aspic}
781 @kbd{tar -cvf afiles.tar apple angst aspic}
785 For more information on option syntax, see @ref{Advanced tar}. In
786 discussions in the text, when we name an option by its long form, we
787 also give the corresponding short option in parentheses.
789 The term, ``option'', can be confusing at times, since ``operations''
790 are often lumped in with the actual, @emph{optional} ``options'' in certain
791 general class statements. For example, we just talked about ``short and
792 long forms of options and operations''. However, experienced @command{tar}
793 users often refer to these by shorthand terms such as, ``short and long
794 options''. This term assumes that the ``operations'' are included, also.
795 Context will help you determine which definition of ``options'' to use.
797 Similarly, the term ``command'' can be confusing, as it is often used in
798 two different ways. People sometimes refer to @command{tar} ``commands''.
799 A @command{tar} @dfn{command} is the entire command line of user input
800 which tells @command{tar} what to do --- including the operation, options,
801 and any arguments (file names, pipes, other commands, etc.). However,
802 you will also sometimes hear the term ``the @command{tar} command''. When
803 the word ``command'' is used specifically like this, a person is usually
804 referring to the @command{tar} @emph{operation}, not the whole line.
805 Again, use context to figure out which of the meanings the speaker
808 @node frequent operations
809 @section The Three Most Frequently Used Operations
811 Here are the three most frequently used operations (both short and long
812 forms), as well as a brief description of their meanings. The rest of
813 this chapter will cover how to use these operations in detail. We will
814 present the rest of the operations in the next chapter.
819 Create a new @command{tar} archive.
822 List the contents of an archive.
825 Extract one or more members from an archive.
828 @node Two Frequent Options
829 @section Two Frequently Used Options
831 To understand how to run @command{tar} in the three operating modes listed
832 previously, you also need to understand how to use two of the options to
833 @command{tar}: @option{--file} (which takes an archive file as an argument)
834 and @option{--verbose}. (You are usually not @emph{required} to specify
835 either of these options when you run @command{tar}, but they can be very
836 useful in making things more clear and helping you avoid errors.)
845 @unnumberedsubsec The @option{--file} Option
848 @xopindex{file, tutorial}
849 @item --file=@var{archive-name}
850 @itemx -f @var{archive-name}
851 Specify the name of an archive file.
854 You can specify an argument for the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option whenever you
855 use @command{tar}; this option determines the name of the archive file
856 that @command{tar} will work on.
859 If you don't specify this argument, then @command{tar} will examine
860 the environment variable @env{TAPE}. If it is set, its value will be
861 used as the archive name. Otherwise, @command{tar} will use the
862 default archive, determined at the compile time. Usually it is
863 standard output or some physical tape drive attached to your machine
864 (you can verify what the default is by running @kbd{tar
865 --show-defaults}, @pxref{defaults}). If there is no tape drive
866 attached, or the default is not meaningful, then @command{tar} will
867 print an error message. The error message might look roughly like one
871 tar: can't open /dev/rmt8 : No such device or address
872 tar: can't open /dev/rsmt0 : I/O error
876 To avoid confusion, we recommend that you always specify an archive file
877 name by using @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) when writing your @command{tar} commands.
878 For more information on using the @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) option, see
881 @node verbose tutorial
882 @unnumberedsubsec The @option{--verbose} Option
885 @xopindex{verbose, introduced}
888 Show the files being worked on as @command{tar} is running.
891 @option{--verbose} (@option{-v}) shows details about the results of running
892 @command{tar}. This can be especially useful when the results might not be
893 obvious. For example, if you want to see the progress of @command{tar} as
894 it writes files into the archive, you can use the @option{--verbose}
895 option. In the beginning, you may find it useful to use
896 @option{--verbose} at all times; when you are more accustomed to
897 @command{tar}, you will likely want to use it at certain times but not at
898 others. We will use @option{--verbose} at times to help make something
899 clear, and we will give many examples both using and not using
900 @option{--verbose} to show the differences.
902 Each instance of @option{--verbose} on the command line increases the
903 verbosity level by one, so if you need more details on the output,
906 When reading archives (@option{--list}, @option{--extract},
907 @option{--diff}), @command{tar} by default prints only the names of
908 the members being extracted. Using @option{--verbose} will show a full,
909 @command{ls} style member listing.
911 In contrast, when writing archives (@option{--create}, @option{--append},
912 @option{--update}), @command{tar} does not print file names by
913 default. So, a single @option{--verbose} option shows the file names
914 being added to the archive, while two @option{--verbose} options
915 enable the full listing.
917 For example, to create an archive in verbose mode:
920 $ @kbd{tar -cvf afiles.tar apple angst aspic}
927 Creating the same archive with the verbosity level 2 could give:
930 $ @kbd{tar -cvvf afiles.tar apple angst aspic}
931 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
932 -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst
933 -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic
937 This works equally well using short or long forms of options. Using
938 long forms, you would simply write out the mnemonic form of the option
942 $ @kbd{tar --create --verbose --verbose @dots{}}
946 Note that you must double the hyphens properly each time.
948 Later in the tutorial, we will give examples using @w{@option{--verbose
951 @anchor{verbose member listing}
952 The full output consists of six fields:
955 @item File type and permissions in symbolic form.
956 These are displayed in the same format as the first column of
957 @command{ls -l} output (@pxref{What information is listed,
958 format=verbose, Verbose listing, fileutils, GNU file utilities}).
960 @item Owner name and group separated by a slash character.
961 If these data are not available (for example, when listing a @samp{v7} format
962 archive), numeric @acronym{ID} values are printed instead.
964 @item Size of the file, in bytes.
966 @item File modification date in ISO 8601 format.
968 @item File modification time.
971 If the name contains any special characters (white space, newlines,
972 etc.) these are displayed in an unambiguous form using so called
973 @dfn{quoting style}. For the detailed discussion of available styles
974 and on how to use them, see @ref{quoting styles}.
976 Depending on the file type, the name can be followed by some
977 additional information, described in the following table:
980 @item -> @var{link-name}
981 The file or archive member is a @dfn{symbolic link} and
982 @var{link-name} is the name of file it links to.
984 @item link to @var{link-name}
985 The file or archive member is a @dfn{hard link} and @var{link-name} is
986 the name of file it links to.
989 The archive member is an old GNU format long link. You will normally
993 The archive member is an old GNU format long name. You will normally
996 @item --Volume Header--
997 The archive member is a GNU @dfn{volume header} (@pxref{Tape Files}).
999 @item --Continued at byte @var{n}--
1000 Encountered only at the beginning of a multi-volume archive
1001 (@pxref{Using Multiple Tapes}). This archive member is a continuation
1002 from the previous volume. The number @var{n} gives the offset where
1003 the original file was split.
1005 @item unknown file type @var{c}
1006 An archive member of unknown type. @var{c} is the type character from
1007 the archive header. If you encounter such a message, it means that
1008 either your archive contains proprietary member types @GNUTAR{} is not
1009 able to handle, or the archive is corrupted.
1014 For example, here is an archive listing containing most of the special
1015 suffixes explained above:
1019 V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header--
1020 -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at
1022 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
1023 lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple
1024 -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues
1025 hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues
1033 @unnumberedsubsec Getting Help: Using the @option{--help} Option
1039 The @option{--help} option to @command{tar} prints out a very brief list of
1040 all operations and option available for the current version of
1041 @command{tar} available on your system.
1045 @section How to Create Archives
1048 @cindex Creation of the archive
1049 @cindex Archive, creation of
1050 One of the basic operations of @command{tar} is @option{--create} (@option{-c}), which
1051 you use to create a @command{tar} archive. We will explain
1052 @option{--create} first because, in order to learn about the other
1053 operations, you will find it useful to have an archive available to
1056 To make this easier, in this section you will first create a directory
1057 containing three files. Then, we will show you how to create an
1058 @emph{archive} (inside the new directory). Both the directory, and
1059 the archive are specifically for you to practice on. The rest of this
1060 chapter and the next chapter will show many examples using this
1061 directory and the files you will create: some of those files may be
1062 other directories and other archives.
1064 The three files you will archive in this example are called
1065 @file{blues}, @file{folk}, and @file{jazz}. The archive is called
1066 @file{collection.tar}.
1068 This section will proceed slowly, detailing how to use @option{--create}
1069 in @code{verbose} mode, and showing examples using both short and long
1070 forms. In the rest of the tutorial, and in the examples in the next
1071 chapter, we will proceed at a slightly quicker pace. This section
1072 moves more slowly to allow beginning users to understand how
1073 @command{tar} works.
1076 * prepare for examples::
1077 * Creating the archive::
1083 @node prepare for examples
1084 @subsection Preparing a Practice Directory for Examples
1086 To follow along with this and future examples, create a new directory
1087 called @file{practice} containing files called @file{blues}, @file{folk}
1088 and @file{jazz}. The files can contain any information you like:
1089 ideally, they should contain information which relates to their names,
1090 and be of different lengths. Our examples assume that @file{practice}
1091 is a subdirectory of your home directory.
1093 Now @command{cd} to the directory named @file{practice}; @file{practice}
1094 is now your @dfn{working directory}. (@emph{Please note}: Although
1095 the full file name of this directory is
1096 @file{/@var{homedir}/practice}, in our examples we will refer to
1097 this directory as @file{practice}; the @var{homedir} is presumed.
1099 In general, you should check that the files to be archived exist where
1100 you think they do (in the working directory) by running @command{ls}.
1101 Because you just created the directory and the files and have changed to
1102 that directory, you probably don't need to do that this time.
1104 It is very important to make sure there isn't already a file in the
1105 working directory with the archive name you intend to use (in this case,
1106 @samp{collection.tar}), or that you don't care about its contents.
1107 Whenever you use @samp{create}, @command{tar} will erase the current
1108 contents of the file named by @option{--file=@var{archive-name}} (@option{-f @var{archive-name}}) if it exists. @command{tar}
1109 will not tell you if you are about to overwrite an archive unless you
1110 specify an option which does this (@pxref{backup}, for the
1111 information on how to do so). To add files to an existing archive,
1112 you need to use a different option, such as @option{--append} (@option{-r}); see
1113 @ref{append} for information on how to do this.
1115 @node Creating the archive
1116 @subsection Creating the Archive
1118 @xopindex{create, introduced}
1119 To place the files @file{blues}, @file{folk}, and @file{jazz} into an
1120 archive named @file{collection.tar}, use the following command:
1123 $ @kbd{tar --create --file=collection.tar blues folk jazz}
1126 The order of the arguments is not very important, @emph{when using long
1127 option forms}. You could also say:
1130 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1134 However, you can see that this order is harder to understand; this is
1135 why we will list the arguments in the order that makes the commands
1136 easiest to understand (and we encourage you to do the same when you use
1137 @command{tar}, to avoid errors).
1139 Note that the sequence
1140 @option{--file=@-collection.tar} is considered to be @emph{one} argument.
1141 If you substituted any other string of characters for
1142 @kbd{collection.tar}, then that string would become the name of the
1143 archive file you create.
1145 The order of the options becomes more important when you begin to use
1146 short forms. With short forms, if you type commands in the wrong order
1147 (even if you type them correctly in all other ways), you may end up with
1148 results you don't expect. For this reason, it is a good idea to get
1149 into the habit of typing options in the order that makes inherent sense.
1150 @xref{short create}, for more information on this.
1152 In this example, you type the command as shown above: @option{--create}
1153 is the operation which creates the new archive
1154 (@file{collection.tar}), and @option{--file} is the option which lets
1155 you give it the name you chose. The files, @file{blues}, @file{folk},
1156 and @file{jazz}, are now members of the archive, @file{collection.tar}
1157 (they are @dfn{file name arguments} to the @option{--create} operation.
1158 @xref{Choosing}, for the detailed discussion on these.) Now that they are
1159 in the archive, they are called @emph{archive members}, not files.
1160 (@pxref{Definitions,members}).
1162 When you create an archive, you @emph{must} specify which files you
1163 want placed in the archive. If you do not specify any archive
1164 members, @GNUTAR{} will complain.
1166 If you now list the contents of the working directory (@command{ls}), you will
1167 find the archive file listed as well as the files you saw previously:
1170 blues folk jazz collection.tar
1174 Creating the archive @samp{collection.tar} did not destroy the copies of
1175 the files in the directory.
1177 Keep in mind that if you don't indicate an operation, @command{tar} will not
1178 run and will prompt you for one. If you don't name any files, @command{tar}
1179 will complain. You must have write access to the working directory,
1180 or else you will not be able to create an archive in that directory.
1182 @emph{Caution}: Do not attempt to use @option{--create} (@option{-c}) to add files to
1183 an existing archive; it will delete the archive and write a new one.
1184 Use @option{--append} (@option{-r}) instead. @xref{append}.
1186 @node create verbose
1187 @subsection Running @option{--create} with @option{--verbose}
1189 @xopindex{create, using with @option{--verbose}}
1190 @xopindex{verbose, using with @option{--create}}
1191 If you include the @option{--verbose} (@option{-v}) option on the command line,
1192 @command{tar} will list the files it is acting on as it is working. In
1193 verbose mode, the @code{create} example above would appear as:
1196 $ @kbd{tar --create --verbose --file=collection.tar blues folk jazz}
1202 This example is just like the example we showed which did not use
1203 @option{--verbose}, except that @command{tar} generated the remaining lines
1205 (note the different font styles).
1211 In the rest of the examples in this chapter, we will frequently use
1212 @code{verbose} mode so we can show actions or @command{tar} responses that
1213 you would otherwise not see, and which are important for you to
1217 @subsection Short Forms with @samp{create}
1219 As we said before, the @option{--create} (@option{-c}) operation is one of the most
1220 basic uses of @command{tar}, and you will use it countless times.
1221 Eventually, you will probably want to use abbreviated (or ``short'')
1222 forms of options. A full discussion of the three different forms that
1223 options can take appears in @ref{Styles}; for now, here is what the
1224 previous example (including the @option{--verbose} (@option{-v}) option) looks like
1225 using short option forms:
1228 $ @kbd{tar -cvf collection.tar blues folk jazz}
1235 As you can see, the system responds the same no matter whether you use
1236 long or short option forms.
1238 @FIXME{i don't like how this is worded:} One difference between using
1239 short and long option forms is that, although the exact placement of
1240 arguments following options is no more specific when using short forms,
1241 it is easier to become confused and make a mistake when using short
1242 forms. For example, suppose you attempted the above example in the
1246 $ @kbd{tar -cfv collection.tar blues folk jazz}
1250 In this case, @command{tar} will make an archive file called @file{v},
1251 containing the files @file{blues}, @file{folk}, and @file{jazz}, because
1252 the @samp{v} is the closest ``file name'' to the @option{-f} option, and
1253 is thus taken to be the chosen archive file name. @command{tar} will try
1254 to add a file called @file{collection.tar} to the @file{v} archive file;
1255 if the file @file{collection.tar} did not already exist, @command{tar} will
1256 report an error indicating that this file does not exist. If the file
1257 @file{collection.tar} does already exist (e.g., from a previous command
1258 you may have run), then @command{tar} will add this file to the archive.
1259 Because the @option{-v} option did not get registered, @command{tar} will not
1260 run under @samp{verbose} mode, and will not report its progress.
1262 The end result is that you may be quite confused about what happened,
1263 and possibly overwrite a file. To illustrate this further, we will show
1264 you how an example we showed previously would look using short forms.
1269 $ @kbd{tar blues --create folk --file=collection.tar jazz}
1273 is confusing as it is. When shown using short forms, however, it
1274 becomes much more so:
1277 $ @kbd{tar blues -c folk -f collection.tar jazz}
1281 It would be very easy to put the wrong string of characters
1282 immediately following the @option{-f}, but doing that could sacrifice
1285 For this reason, we recommend that you pay very careful attention to
1286 the order of options and placement of file and archive names,
1287 especially when using short option forms. Not having the option name
1288 written out mnemonically can affect how well you remember which option
1289 does what, and therefore where different names have to be placed.
1292 @subsection Archiving Directories
1294 @cindex Archiving Directories
1295 @cindex Directories, Archiving
1296 You can archive a directory by specifying its directory name as a
1297 file name argument to @command{tar}. The files in the directory will be
1298 archived relative to the working directory, and the directory will be
1299 re-created along with its contents when the archive is extracted.
1301 To archive a directory, first move to its superior directory. If you
1302 have followed the previous instructions in this tutorial, you should
1311 This will put you into the directory which contains @file{practice},
1312 i.e., your home directory. Once in the superior directory, you can
1313 specify the subdirectory, @file{practice}, as a file name argument. To
1314 store @file{practice} in the new archive file @file{music.tar}, type:
1317 $ @kbd{tar --create --verbose --file=music.tar practice}
1321 @command{tar} should output:
1328 practice/collection.tar
1331 Note that the archive thus created is not in the subdirectory
1332 @file{practice}, but rather in the current working directory---the
1333 directory from which @command{tar} was invoked. Before trying to archive a
1334 directory from its superior directory, you should make sure you have
1335 write access to the superior directory itself, not only the directory
1336 you are trying archive with @command{tar}. For example, you will probably
1337 not be able to store your home directory in an archive by invoking
1338 @command{tar} from the root directory; @xref{absolute}. (Note
1339 also that @file{collection.tar}, the original archive file, has itself
1340 been archived. @command{tar} will accept any file as a file to be
1341 archived, regardless of its content. When @file{music.tar} is
1342 extracted, the archive file @file{collection.tar} will be re-written
1343 into the file system).
1345 If you give @command{tar} a command such as
1348 $ @kbd{tar --create --file=foo.tar .}
1352 @command{tar} will report @samp{tar: ./foo.tar is the archive; not
1353 dumped}. This happens because @command{tar} creates the archive
1354 @file{foo.tar} in the current directory before putting any files into
1355 it. Then, when @command{tar} attempts to add all the files in the
1356 directory @file{.} to the archive, it notices that the file
1357 @file{./foo.tar} is the same as the archive @file{foo.tar}, and skips
1358 it. (It makes no sense to put an archive into itself.) @GNUTAR{}
1359 will continue in this case, and create the archive
1360 normally, except for the exclusion of that one file. (@emph{Please
1361 note:} Other implementations of @command{tar} may not be so clever;
1362 they will enter an infinite loop when this happens, so you should not
1363 depend on this behavior unless you are certain you are running
1364 @GNUTAR{}. In general, it is wise to always place the archive outside
1365 of the directory being dumped.
1368 @section How to List Archives
1371 Frequently, you will find yourself wanting to determine exactly what a
1372 particular archive contains. You can use the @option{--list}
1373 (@option{-t}) operation to get the member names as they currently
1374 appear in the archive, as well as various attributes of the files at
1375 the time they were archived. For example, you can examine the archive
1376 @file{collection.tar} that you created in the last section with the
1380 $ @kbd{tar --list --file=collection.tar}
1384 The output of @command{tar} would then be:
1393 The archive @file{bfiles.tar} would list as follows:
1402 Be sure to use a @option{--file=@var{archive-name}} (@option{-f
1403 @var{archive-name}}) option just as with @option{--create}
1404 (@option{-c}) to specify the name of the archive.
1406 @xopindex{list, using with @option{--verbose}}
1407 @xopindex{verbose, using with @option{--list}}
1408 If you use the @option{--verbose} (@option{-v}) option with
1409 @option{--list}, then @command{tar} will print out a listing
1410 reminiscent of @w{@samp{ls -l}}, showing owner, file size, and so
1411 forth. This output is described in detail in @ref{verbose member listing}.
1413 If you had used @option{--verbose} (@option{-v}) mode, the example
1414 above would look like:
1417 $ @kbd{tar --list --verbose --file=collection.tar folk}
1418 -rw-r--r-- myself user 62 1990-05-23 10:55 folk
1421 @cindex listing member and file names
1422 @anchor{listing member and file names}
1423 It is important to notice that the output of @kbd{tar --list
1424 --verbose} does not necessarily match that produced by @kbd{tar
1425 --create --verbose} while creating the archive. It is because
1426 @GNUTAR{}, unless told explicitly not to do so, removes some directory
1427 prefixes from file names before storing them in the archive
1428 (@xref{absolute}, for more information). In other
1429 words, in verbose mode @GNUTAR{} shows @dfn{file names} when creating
1430 an archive and @dfn{member names} when listing it. Consider this
1435 $ @kbd{tar --create --verbose --file archive /etc/mail}
1436 tar: Removing leading `/' from member names
1438 /etc/mail/sendmail.cf
1440 $ @kbd{tar --test --file archive}
1442 etc/mail/sendmail.cf
1447 @opindex show-stored-names
1448 This default behavior can sometimes be inconvenient. You can force
1449 @GNUTAR{} show member names when creating archive by supplying
1450 @option{--show-stored-names} option.
1453 @item --show-stored-names
1454 Print member (as opposed to @emph{file}) names when creating the archive.
1457 @cindex File name arguments, using @option{--list} with
1458 @xopindex{list, using with file name arguments}
1459 You can specify one or more individual member names as arguments when
1460 using @samp{list}. In this case, @command{tar} will only list the
1461 names of members you identify. For example, @w{@kbd{tar --list
1462 --file=afiles.tar apple}} would only print @file{apple}.
1464 Because @command{tar} preserves file names, these must be specified as
1465 they appear in the archive (i.e., relative to the directory from which
1466 the archive was created). Therefore, it is essential when specifying
1467 member names to @command{tar} that you give the exact member names.
1468 For example, @w{@kbd{tar --list --file=bfiles.tar birds}} would produce an
1469 error message something like @samp{tar: birds: Not found in archive},
1470 because there is no member named @file{birds}, only one named
1471 @file{./birds}. While the names @file{birds} and @file{./birds} name
1472 the same file, @emph{member} names by default are compared verbatim.
1474 However, @w{@kbd{tar --list --file=bfiles.tar baboon}} would respond
1475 with @file{baboon}, because this exact member name is in the archive file
1476 @file{bfiles.tar}. If you are not sure of the exact file name,
1477 use @dfn{globbing patterns}, for example:
1480 $ @kbd{tar --list --file=bfiles.tar --wildcards '*b*'}
1484 will list all members whose name contains @samp{b}. @xref{wildcards},
1485 for a detailed discussion of globbing patterns and related
1486 @command{tar} command line options.
1493 @unnumberedsubsec Listing the Contents of a Stored Directory
1495 To get information about the contents of an archived directory,
1496 use the directory name as a file name argument in conjunction with
1497 @option{--list} (@option{-t}). To find out file attributes, include the
1498 @option{--verbose} (@option{-v}) option.
1500 For example, to find out about files in the directory @file{practice}, in
1501 the archive file @file{music.tar}, type:
1504 $ @kbd{tar --list --verbose --file=music.tar practice}
1507 @command{tar} responds:
1510 drwxrwxrwx myself user 0 1990-05-31 21:49 practice/
1511 -rw-r--r-- myself user 42 1990-05-21 13:29 practice/blues
1512 -rw-r--r-- myself user 62 1990-05-23 10:55 practice/folk
1513 -rw-r--r-- myself user 40 1990-05-21 13:30 practice/jazz
1514 -rw-r--r-- myself user 10240 1990-05-31 21:49 practice/collection.tar
1517 When you use a directory name as a file name argument, @command{tar} acts on
1518 all the files (including sub-directories) in that directory.
1521 @section How to Extract Members from an Archive
1523 @cindex Retrieving files from an archive
1524 @cindex Resurrecting files from an archive
1527 Creating an archive is only half the job---there is no point in storing
1528 files in an archive if you can't retrieve them. The act of retrieving
1529 members from an archive so they can be used and manipulated as
1530 unarchived files again is called @dfn{extraction}. To extract files
1531 from an archive, use the @option{--extract} (@option{--get} or
1532 @option{-x}) operation. As with @option{--create}, specify the name
1533 of the archive with @option{--file} (@option{-f}) option. Extracting
1534 an archive does not modify the archive in any way; you can extract it
1535 multiple times if you want or need to.
1537 Using @option{--extract}, you can extract an entire archive, or specific
1538 files. The files can be directories containing other files, or not. As
1539 with @option{--create} (@option{-c}) and @option{--list} (@option{-t}), you may use the short or the
1540 long form of the operation without affecting the performance.
1543 * extracting archives::
1544 * extracting files::
1546 * extracting untrusted archives::
1547 * failing commands::
1550 @node extracting archives
1551 @subsection Extracting an Entire Archive
1553 To extract an entire archive, specify the archive file name only, with
1554 no individual file names as arguments. For example,
1557 $ @kbd{tar -xvf collection.tar}
1564 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
1565 -rw-r--r-- me user 21 1996-09-23 16:44 blues
1566 -rw-r--r-- me user 20 1996-09-23 16:44 folk
1569 @node extracting files
1570 @subsection Extracting Specific Files
1572 To extract specific archive members, give their exact member names as
1573 arguments, as printed by @option{--list} (@option{-t}). If you had
1574 mistakenly deleted one of the files you had placed in the archive
1575 @file{collection.tar} earlier (say, @file{blues}), you can extract it
1576 from the archive without changing the archive's structure. Its
1577 contents will be identical to the original file @file{blues} that you
1580 First, make sure you are in the @file{practice} directory, and list the
1581 files in the directory. Now, delete the file, @samp{blues}, and list
1582 the files in the directory again.
1584 You can now extract the member @file{blues} from the archive file
1585 @file{collection.tar} like this:
1588 $ @kbd{tar --extract --file=collection.tar blues}
1592 If you list the files in the directory again, you will see that the file
1593 @file{blues} has been restored, with its original permissions, data
1594 modification times, and owner.@footnote{This is only accidentally
1595 true, but not in general. Whereas modification times are always
1596 restored, in most cases, one has to be root for restoring the owner,
1597 and use a special option for restoring permissions. Here, it just
1598 happens that the restoring user is also the owner of the archived
1599 members, and that the current @code{umask} is compatible with original
1600 permissions.} (These parameters will be identical to those which
1601 the file had when you originally placed it in the archive; any changes
1602 you may have made before deleting the file from the file system,
1603 however, will @emph{not} have been made to the archive member.) The
1604 archive file, @samp{collection.tar}, is the same as it was before you
1605 extracted @samp{blues}. You can confirm this by running @command{tar} with
1606 @option{--list} (@option{-t}).
1608 Remember that as with other operations, specifying the exact member
1609 name is important. @w{@kbd{tar --extract --file=bfiles.tar birds}}
1610 will fail, because there is no member named @file{birds}. To extract
1611 the member named @file{./birds}, you must specify @w{@kbd{tar
1612 --extract --file=bfiles.tar ./birds}}. If you don't remember the
1613 exact member names, use @option{--list} (@option{-t}) option
1614 (@pxref{list}). You can also extract those members that match a
1615 specific @dfn{globbing pattern}. For example, to extract from
1616 @file{bfiles.tar} all files that begin with @samp{b}, no matter their
1617 directory prefix, you could type:
1620 $ @kbd{tar -x -f bfiles.tar --wildcards --no-anchored 'b*'}
1624 Here, @option{--wildcards} instructs @command{tar} to treat
1625 command line arguments as globbing patterns and @option{--no-anchored}
1626 informs it that the patterns apply to member names after any @samp{/}
1627 delimiter. The use of globbing patterns is discussed in detail in
1630 You can extract a file to standard output by combining the above options
1631 with the @option{--to-stdout} (@option{-O}) option (@pxref{Writing to Standard
1634 If you give the @option{--verbose} option, then @option{--extract}
1635 will print the names of the archive members as it extracts them.
1638 @subsection Extracting Files that are Directories
1640 Extracting directories which are members of an archive is similar to
1641 extracting other files. The main difference to be aware of is that if
1642 the extracted directory has the same name as any directory already in
1643 the working directory, then files in the extracted directory will be
1644 placed into the directory of the same name. Likewise, if there are
1645 files in the pre-existing directory with the same names as the members
1646 which you extract, the files from the extracted archive will replace
1647 the files already in the working directory (and possible
1648 subdirectories). This will happen regardless of whether or not the
1649 files in the working directory were more recent than those extracted
1650 (there exist, however, special options that alter this behavior
1653 However, if a file was stored with a directory name as part of its file
1654 name, and that directory does not exist under the working directory when
1655 the file is extracted, @command{tar} will create the directory.
1657 We can demonstrate how to use @option{--extract} to extract a directory
1658 file with an example. Change to the @file{practice} directory if you
1659 weren't there, and remove the files @file{folk} and @file{jazz}. Then,
1660 go back to the parent directory and extract the archive
1661 @file{music.tar}. You may either extract the entire archive, or you may
1662 extract only the files you just deleted. To extract the entire archive,
1663 don't give any file names as arguments after the archive name
1664 @file{music.tar}. To extract only the files you deleted, use the
1668 $ @kbd{tar -xvf music.tar practice/folk practice/jazz}
1674 If you were to specify two @option{--verbose} (@option{-v}) options, @command{tar}
1675 would have displayed more detail about the extracted files, as shown
1676 in the example below:
1679 $ @kbd{tar -xvvf music.tar practice/folk practice/jazz}
1680 -rw-r--r-- me user 28 1996-10-18 16:31 practice/jazz
1681 -rw-r--r-- me user 20 1996-09-23 16:44 practice/folk
1685 Because you created the directory with @file{practice} as part of the
1686 file names of each of the files by archiving the @file{practice}
1687 directory as @file{practice}, you must give @file{practice} as part
1688 of the file names when you extract those files from the archive.
1690 @node extracting untrusted archives
1691 @subsection Extracting Archives from Untrusted Sources
1693 Extracting files from archives can overwrite files that already exist.
1694 If you receive an archive from an untrusted source, you should make a
1695 new directory and extract into that directory, so that you don't have
1696 to worry about the extraction overwriting one of your existing files.
1697 For example, if @file{untrusted.tar} came from somewhere else on the
1698 Internet, and you don't necessarily trust its contents, you can
1699 extract it as follows:
1702 $ @kbd{mkdir newdir}
1704 $ @kbd{tar -xvf ../untrusted.tar}
1707 It is also a good practice to examine contents of the archive
1708 before extracting it, using @option{--list} (@option{-t}) option, possibly combined
1709 with @option{--verbose} (@option{-v}).
1711 @node failing commands
1712 @subsection Commands That Will Fail
1714 Here are some sample commands you might try which will not work, and why
1717 If you try to use this command,
1720 $ @kbd{tar -xvf music.tar folk jazz}
1724 you will get the following response:
1727 tar: folk: Not found in archive
1728 tar: jazz: Not found in archive
1733 This is because these files were not originally @emph{in} the parent
1734 directory @file{..}, where the archive is located; they were in the
1735 @file{practice} directory, and their file names reflect this:
1738 $ @kbd{tar -tvf music.tar}
1744 @FIXME{make sure the above works when going through the examples in
1748 Likewise, if you try to use this command,
1751 $ @kbd{tar -tvf music.tar folk jazz}
1755 you would get a similar response. Members with those names are not in the
1756 archive. You must use the correct member names, or wildcards, in order
1757 to extract the files from the archive.
1759 If you have forgotten the correct names of the files in the archive,
1760 use @w{@kbd{tar --list --verbose}} to list them correctly.
1762 @FIXME{more examples, here? hag thinks it's a good idea.}
1765 @section Going Further Ahead in this Manual
1768 @FIXME{need to write up a node here about the things that are going to
1769 be in the rest of the manual.}
1771 @node tar invocation
1772 @chapter Invoking @GNUTAR{}
1774 This chapter is about how one invokes the @GNUTAR{}
1775 command, from the command synopsis (@pxref{Synopsis}). There are
1776 numerous options, and many styles for writing them. One mandatory
1777 option specifies the operation @command{tar} should perform
1778 (@pxref{Operation Summary}), other options are meant to detail how
1779 this operation should be performed (@pxref{Option Summary}).
1780 Non-option arguments are not always interpreted the same way,
1781 depending on what the operation is.
1783 You will find in this chapter everything about option styles and rules for
1784 writing them (@pxref{Styles}). On the other hand, operations and options
1785 are fully described elsewhere, in other chapters. Here, you will find
1786 only synthetic descriptions for operations and options, together with
1787 pointers to other parts of the @command{tar} manual.
1789 Some options are so special they are fully described right in this
1790 chapter. They have the effect of inhibiting the normal operation of
1791 @command{tar} or else, they globally alter the amount of feedback the user
1792 receives about what is going on. These are the @option{--help} and
1793 @option{--version} (@pxref{help}), @option{--verbose} (@pxref{verbose})
1794 and @option{--interactive} options (@pxref{interactive}).
1798 * using tar options::
1810 @section General Synopsis of @command{tar}
1812 The @GNUTAR{} program is invoked as either one of:
1815 @kbd{tar @var{option}@dots{} [@var{name}]@dots{}}
1816 @kbd{tar @var{letter}@dots{} [@var{argument}]@dots{} [@var{option}]@dots{} [@var{name}]@dots{}}
1819 The second form is for when old options are being used.
1821 You can use @command{tar} to store files in an archive, to extract them from
1822 an archive, and to do other types of archive manipulation. The primary
1823 argument to @command{tar}, which is called the @dfn{operation}, specifies
1824 which action to take. The other arguments to @command{tar} are either
1825 @dfn{options}, which change the way @command{tar} performs an operation,
1826 or file names or archive members, which specify the files or members
1827 @command{tar} is to act on.
1829 You can actually type in arguments in any order, even if in this manual
1830 the options always precede the other arguments, to make examples easier
1831 to understand. Further, the option stating the main operation mode
1832 (the @command{tar} main command) is usually given first.
1834 Each @var{name} in the synopsis above is interpreted as an archive member
1835 name when the main command is one of @option{--compare}
1836 (@option{--diff}, @option{-d}), @option{--delete}, @option{--extract}
1837 (@option{--get}, @option{-x}), @option{--list} (@option{-t}) or
1838 @option{--update} (@option{-u}). When naming archive members, you
1839 must give the exact name of the member in the archive, as it is
1840 printed by @option{--list}. For @option{--append} (@option{-r}) and
1841 @option{--create} (@option{-c}), these @var{name} arguments specify
1842 the names of either files or directory hierarchies to place in the archive.
1843 These files or hierarchies should already exist in the file system,
1844 prior to the execution of the @command{tar} command.
1846 @command{tar} interprets relative file names as being relative to the
1847 working directory. @command{tar} will make all file names relative
1848 (by removing leading slashes when archiving or restoring files),
1849 unless you specify otherwise (using the @option{--absolute-names}
1850 option). @xref{absolute}, for more information about
1851 @option{--absolute-names}.
1853 If you give the name of a directory as either a file name or a member
1854 name, then @command{tar} acts recursively on all the files and directories
1855 beneath that directory. For example, the name @file{/} identifies all
1856 the files in the file system to @command{tar}.
1858 The distinction between file names and archive member names is especially
1859 important when shell globbing is used, and sometimes a source of confusion
1860 for newcomers. @xref{wildcards}, for more information about globbing.
1861 The problem is that shells may only glob using existing files in the
1862 file system. Only @command{tar} itself may glob on archive members, so when
1863 needed, you must ensure that wildcard characters reach @command{tar} without
1864 being interpreted by the shell first. Using a backslash before @samp{*}
1865 or @samp{?}, or putting the whole argument between quotes, is usually
1866 sufficient for this.
1868 Even if @var{name}s are often specified on the command line, they
1869 can also be read from a text file in the file system, using the
1870 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}}) option.
1872 If you don't use any file name arguments, @option{--append} (@option{-r}),
1873 @option{--delete} and @option{--concatenate} (@option{--catenate},
1874 @option{-A}) will do nothing, while @option{--create} (@option{-c})
1875 will usually yield a diagnostic and inhibit @command{tar} execution.
1876 The other operations of @command{tar} (@option{--list},
1877 @option{--extract}, @option{--compare}, and @option{--update})
1878 will act on the entire contents of the archive.
1881 @cindex return status
1882 Besides successful exits, @GNUTAR{} may fail for
1883 many reasons. Some reasons correspond to bad usage, that is, when the
1884 @command{tar} command line is improperly written. Errors may be
1885 encountered later, while processing the archive or the files. Some
1886 errors are recoverable, in which case the failure is delayed until
1887 @command{tar} has completed all its work. Some errors are such that
1888 it would be not meaningful, or at least risky, to continue processing:
1889 @command{tar} then aborts processing immediately. All abnormal exits,
1890 whether immediate or delayed, should always be clearly diagnosed on
1891 @code{stderr}, after a line stating the nature of the error.
1893 Possible exit codes of @GNUTAR{} are summarized in the following
1898 @samp{Successful termination}.
1901 @samp{Some files differ}. If tar was invoked with @option{--compare}
1902 (@option{--diff}, @option{-d}) command line option, this means that
1903 some files in the archive differ from their disk counterparts
1904 (@pxref{compare}). If tar was given @option{--create},
1905 @option{--append} or @option{--update} option, this exit code means
1906 that some files were changed while being archived and so the resulting
1907 archive does not contain the exact copy of the file set.
1910 @samp{Fatal error}. This means that some fatal, unrecoverable error
1914 If @command{tar} has invoked a subprocess and that subprocess exited with a
1915 nonzero exit code, @command{tar} exits with that code as well.
1916 This can happen, for example, if @command{tar} was given some
1917 compression option (@pxref{gzip}) and the external compressor program
1918 failed. Another example is @command{rmt} failure during backup to the
1919 remote device (@pxref{Remote Tape Server}).
1921 @node using tar options
1922 @section Using @command{tar} Options
1924 @GNUTAR{} has a total of eight operating modes which
1925 allow you to perform a variety of tasks. You are required to choose
1926 one operating mode each time you employ the @command{tar} program by
1927 specifying one, and only one operation as an argument to the
1928 @command{tar} command (the corresponding options may be found
1929 at @ref{frequent operations} and @ref{Operations}). Depending on
1930 circumstances, you may also wish to customize how the chosen operating
1931 mode behaves. For example, you may wish to change the way the output
1932 looks, or the format of the files that you wish to archive may require
1933 you to do something special in order to make the archive look right.
1935 You can customize and control @command{tar}'s performance by running
1936 @command{tar} with one or more options (such as @option{--verbose}
1937 (@option{-v}), which we used in the tutorial). As we said in the
1938 tutorial, @dfn{options} are arguments to @command{tar} which are (as
1939 their name suggests) optional. Depending on the operating mode, you
1940 may specify one or more options. Different options will have different
1941 effects, but in general they all change details of the operation, such
1942 as archive format, archive name, or level of user interaction. Some
1943 options make sense with all operating modes, while others are
1944 meaningful only with particular modes. You will likely use some
1945 options frequently, while you will only use others infrequently, or
1946 not at all. (A full list of options is available in @pxref{All Options}.)
1948 @vrindex TAR_OPTIONS, environment variable
1949 @anchor{TAR_OPTIONS}
1950 The @env{TAR_OPTIONS} environment variable specifies default options to
1951 be placed in front of any explicit options. For example, if
1952 @code{TAR_OPTIONS} is @samp{-v --unlink-first}, @command{tar} behaves as
1953 if the two options @option{-v} and @option{--unlink-first} had been
1954 specified before any explicit options. Option specifications are
1955 separated by whitespace. A backslash escapes the next character, so it
1956 can be used to specify an option containing whitespace or a backslash.
1958 Note that @command{tar} options are case sensitive. For example, the
1959 options @option{-T} and @option{-t} are different; the first requires an
1960 argument for stating the name of a file providing a list of @var{name}s,
1961 while the second does not require an argument and is another way to
1962 write @option{--list} (@option{-t}).
1964 In addition to the eight operations, there are many options to
1965 @command{tar}, and three different styles for writing both: long (mnemonic)
1966 form, short form, and old style. These styles are discussed below.
1967 Both the options and the operations can be written in any of these three
1970 @FIXME{menu at end of this node. need to think of an actual outline
1971 for this chapter; probably do that after stuff from chapter 4 is
1975 @section The Three Option Styles
1977 There are three styles for writing operations and options to the command
1978 line invoking @command{tar}. The different styles were developed at
1979 different times during the history of @command{tar}. These styles will be
1980 presented below, from the most recent to the oldest.
1982 Some options must take an argument. (For example, @option{--file}
1983 (@option{-f})) takes the name of an archive file as an argument. If
1984 you do not supply an archive file name, @command{tar} will use a
1985 default, but this can be confusing; thus, we recommend that you always
1986 supply a specific archive file name.) Where you @emph{place} the
1987 arguments generally depends on which style of options you choose. We
1988 will detail specific information relevant to each option style in the
1989 sections on the different option styles, below. The differences are
1990 subtle, yet can often be very important; incorrect option placement
1991 can cause you to overwrite a number of important files. We urge you
1992 to note these differences, and only use the option style(s) which
1993 makes the most sense to you until you feel comfortable with the others.
1995 Some options @emph{may} take an argument. Such options may have at
1996 most long and short forms, they do not have old style equivalent. The
1997 rules for specifying an argument for such options are stricter than
1998 those for specifying mandatory arguments. Please, pay special
2002 * Long Options:: Long Option Style
2003 * Short Options:: Short Option Style
2004 * Old Options:: Old Option Style
2005 * Mixing:: Mixing Option Styles
2009 @subsection Long Option Style
2011 @cindex long options
2012 @cindex options, long style
2013 @cindex options, GNU style
2014 @cindex options, mnemonic names
2015 Each option has at least one @dfn{long} (or @dfn{mnemonic}) name starting with two
2016 dashes in a row, e.g., @option{--list}. The long names are more clear than
2017 their corresponding short or old names. It sometimes happens that a
2018 single long option has many different names which are
2019 synonymous, such as @option{--compare} and @option{--diff}. In addition,
2020 long option names can be given unique abbreviations. For example,
2021 @option{--cre} can be used in place of @option{--create} because there is no
2022 other long option which begins with @samp{cre}. (One way to find
2023 this out is by trying it and seeing what happens; if a particular
2024 abbreviation could represent more than one option, @command{tar} will tell
2025 you that that abbreviation is ambiguous and you'll know that that
2026 abbreviation won't work. You may also choose to run @samp{tar --help}
2027 to see a list of options. Be aware that if you run @command{tar} with a
2028 unique abbreviation for the long name of an option you didn't want to
2029 use, you are stuck; @command{tar} will perform the command as ordered.)
2031 Long options are meant to be obvious and easy to remember, and their
2032 meanings are generally easier to discern than those of their
2033 corresponding short options (see below). For example:
2036 $ @kbd{tar --create --verbose --blocking-factor=20 --file=/dev/rmt0}
2040 gives a fairly good set of hints about what the command does, even
2041 for those not fully acquainted with @command{tar}.
2043 @cindex arguments to long options
2044 @cindex long options with mandatory arguments
2045 Long options which require arguments take those arguments
2046 immediately following the option name. There are two ways of
2047 specifying a mandatory argument. It can be separated from the
2048 option name either by an equal sign, or by any amount of
2049 white space characters. For example, the @option{--file} option (which
2050 tells the name of the @command{tar} archive) is given a file such as
2051 @file{archive.tar} as argument by using any of the following notations:
2052 @option{--file=archive.tar} or @option{--file archive.tar}.
2054 @cindex optional arguments to long options
2055 @cindex long options with optional arguments
2056 In contrast, optional arguments must always be introduced using
2057 an equal sign. For example, the @option{--backup} option takes
2058 an optional argument specifying backup type. It must be used
2059 as @option{--backup=@var{backup-type}}.
2062 @subsection Short Option Style
2064 @cindex short options
2065 @cindex options, short style
2066 @cindex options, traditional
2067 Most options also have a @dfn{short option} name. Short options start with
2068 a single dash, and are followed by a single character, e.g., @option{-t}
2069 (which is equivalent to @option{--list}). The forms are absolutely
2070 identical in function; they are interchangeable.
2072 The short option names are faster to type than long option names.
2074 @cindex arguments to short options
2075 @cindex short options with mandatory arguments
2076 Short options which require arguments take their arguments immediately
2077 following the option, usually separated by white space. It is also
2078 possible to stick the argument right after the short option name, using
2079 no intervening space. For example, you might write @w{@option{-f
2080 archive.tar}} or @option{-farchive.tar} instead of using
2081 @option{--file=archive.tar}. Both @option{--file=@var{archive-name}} and
2082 @w{@option{-f @var{archive-name}}} denote the option which indicates a
2083 specific archive, here named @file{archive.tar}.
2085 @cindex optional arguments to short options
2086 @cindex short options with optional arguments
2087 Short options which take optional arguments take their arguments
2088 immediately following the option letter, @emph{without any intervening
2089 white space characters}.
2091 Short options' letters may be clumped together, but you are not
2092 required to do this (as compared to old options; see below). When
2093 short options are clumped as a set, use one (single) dash for them
2094 all, e.g., @w{@samp{@command{tar} -cvf}}. Only the last option in
2095 such a set is allowed to have an argument@footnote{Clustering many
2096 options, the last of which has an argument, is a rather opaque way to
2097 write options. Some wonder if @acronym{GNU} @code{getopt} should not
2098 even be made helpful enough for considering such usages as invalid.}.
2100 When the options are separated, the argument for each option which requires
2101 an argument directly follows that option, as is usual for Unix programs.
2105 $ @kbd{tar -c -v -b 20 -f /dev/rmt0}
2108 If you reorder short options' locations, be sure to move any arguments
2109 that belong to them. If you do not move the arguments properly, you may
2110 end up overwriting files.
2113 @subsection Old Option Style
2114 @cindex options, old style
2115 @cindex old option style
2117 Like short options, @dfn{old options} are single letters. However, old options
2118 must be written together as a single clumped set, without spaces separating
2119 them or dashes preceding them@footnote{Beware that if you precede options
2120 with a dash, you are announcing the short option style instead of the
2121 old option style; short options are decoded differently.}. This set
2122 of letters must be the first to appear on the command line, after the
2123 @command{tar} program name and some white space; old options cannot appear
2124 anywhere else. The letter of an old option is exactly the same letter as
2125 the corresponding short option. For example, the old option @samp{t} is
2126 the same as the short option @option{-t}, and consequently, the same as the
2127 long option @option{--list}. So for example, the command @w{@samp{tar
2128 cv}} specifies the option @option{-v} in addition to the operation @option{-c}.
2130 @cindex arguments to old options
2131 @cindex old options with mandatory arguments
2132 When options that need arguments are given together with the command,
2133 all the associated arguments follow, in the same order as the options.
2134 Thus, the example given previously could also be written in the old
2138 $ @kbd{tar cvbf 20 /dev/rmt0}
2142 Here, @samp{20} is the argument of @option{-b} and @samp{/dev/rmt0} is
2143 the argument of @option{-f}.
2145 On the other hand, this old style syntax makes it difficult to match
2146 option letters with their corresponding arguments, and is often
2147 confusing. In the command @w{@samp{tar cvbf 20 /dev/rmt0}}, for example,
2148 @samp{20} is the argument for @option{-b}, @samp{/dev/rmt0} is the
2149 argument for @option{-f}, and @option{-v} does not have a corresponding
2150 argument. Even using short options like in @w{@samp{tar -c -v -b 20 -f
2151 /dev/rmt0}} is clearer, putting all arguments next to the option they
2154 If you want to reorder the letters in the old option argument, be
2155 sure to reorder any corresponding argument appropriately.
2157 This old way of writing @command{tar} options can surprise even experienced
2158 users. For example, the two commands:
2161 @kbd{tar cfz archive.tar.gz file}
2162 @kbd{tar -cfz archive.tar.gz file}
2166 are quite different. The first example uses @file{archive.tar.gz} as
2167 the value for option @samp{f} and recognizes the option @samp{z}. The
2168 second example, however, uses @file{z} as the value for option
2169 @samp{f} --- probably not what was intended.
2171 Old options are kept for compatibility with old versions of @command{tar}.
2173 This second example could be corrected in many ways, among which the
2174 following are equivalent:
2177 @kbd{tar -czf archive.tar.gz file}
2178 @kbd{tar -cf archive.tar.gz -z file}
2179 @kbd{tar cf archive.tar.gz -z file}
2182 @cindex option syntax, traditional
2183 As far as we know, all @command{tar} programs, @acronym{GNU} and
2184 non-@acronym{GNU}, support old options. @GNUTAR{}
2185 supports them not only for historical reasons, but also because many
2186 people are used to them. For compatibility with Unix @command{tar},
2187 the first argument is always treated as containing command and option
2188 letters even if it doesn't start with @samp{-}. Thus, @samp{tar c} is
2189 equivalent to @w{@samp{tar -c}:} both of them specify the
2190 @option{--create} (@option{-c}) command to create an archive.
2193 @subsection Mixing Option Styles
2195 @cindex options, mixing different styles
2196 All three styles may be intermixed in a single @command{tar} command,
2197 so long as the rules for each style are fully
2198 respected@footnote{Before @GNUTAR{} version 1.11.6,
2199 a bug prevented intermixing old style options with long options in
2200 some cases.}. Old style options and either of the modern styles of
2201 options may be mixed within a single @command{tar} command. However,
2202 old style options must be introduced as the first arguments only,
2203 following the rule for old options (old options must appear directly
2204 after the @command{tar} command and some white space). Modern options
2205 may be given only after all arguments to the old options have been
2206 collected. If this rule is not respected, a modern option might be
2207 falsely interpreted as the value of the argument to one of the old
2210 For example, all the following commands are wholly equivalent, and
2211 illustrate the many combinations and orderings of option styles.
2214 @kbd{tar --create --file=archive.tar}
2215 @kbd{tar --create -f archive.tar}
2216 @kbd{tar --create -farchive.tar}
2217 @kbd{tar --file=archive.tar --create}
2218 @kbd{tar --file=archive.tar -c}
2219 @kbd{tar -c --file=archive.tar}
2220 @kbd{tar -c -f archive.tar}
2221 @kbd{tar -c -farchive.tar}
2222 @kbd{tar -cf archive.tar}
2223 @kbd{tar -cfarchive.tar}
2224 @kbd{tar -f archive.tar --create}
2225 @kbd{tar -f archive.tar -c}
2226 @kbd{tar -farchive.tar --create}
2227 @kbd{tar -farchive.tar -c}
2228 @kbd{tar c --file=archive.tar}
2229 @kbd{tar c -f archive.tar}
2230 @kbd{tar c -farchive.tar}
2231 @kbd{tar cf archive.tar}
2232 @kbd{tar f archive.tar --create}
2233 @kbd{tar f archive.tar -c}
2234 @kbd{tar fc archive.tar}
2237 On the other hand, the following commands are @emph{not} equivalent to
2241 @kbd{tar -f -c archive.tar}
2242 @kbd{tar -fc archive.tar}
2243 @kbd{tar -fcarchive.tar}
2244 @kbd{tar -farchive.tarc}
2245 @kbd{tar cfarchive.tar}
2249 These last examples mean something completely different from what the
2250 user intended (judging based on the example in the previous set which
2251 uses long options, whose intent is therefore very clear). The first
2252 four specify that the @command{tar} archive would be a file named
2253 @option{-c}, @samp{c}, @samp{carchive.tar} or @samp{archive.tarc},
2254 respectively. The first two examples also specify a single non-option,
2255 @var{name} argument having the value @samp{archive.tar}. The last
2256 example contains only old style option letters (repeating option
2257 @samp{c} twice), not all of which are meaningful (eg., @samp{.},
2258 @samp{h}, or @samp{i}), with no argument value. @FIXME{not sure i liked
2259 the first sentence of this paragraph..}
2262 @section All @command{tar} Options
2264 The coming manual sections contain an alphabetical listing of all
2265 @command{tar} operations and options, with brief descriptions and cross
2266 references to more in-depth explanations in the body of the manual.
2267 They also contain an alphabetically arranged table of the short option
2268 forms with their corresponding long option. You can use this table as
2269 a reference for deciphering @command{tar} commands in scripts.
2272 * Operation Summary::
2274 * Short Option Summary::
2277 @node Operation Summary
2278 @subsection Operations
2286 Appends files to the end of the archive. @xref{append}.
2288 @opsummary{catenate}
2292 Same as @option{--concatenate}. @xref{concatenate}.
2298 Compares archive members with their counterparts in the file
2299 system, and reports differences in file size, mode, owner,
2300 modification date and contents. @xref{compare}.
2302 @opsummary{concatenate}
2306 Appends other @command{tar} archives to the end of the archive.
2313 Creates a new @command{tar} archive. @xref{create}.
2318 Deletes members from the archive. Don't try this on a archive on a
2319 tape! @xref{delete}.
2325 Same @option{--compare}. @xref{compare}.
2331 Extracts members from the archive into the file system. @xref{extract}.
2337 Same as @option{--extract}. @xref{extract}.
2343 Lists the members in an archive. @xref{list}.
2349 Adds files to the end of the archive, but only if they are newer than
2350 their counterparts already in the archive, or if they do not already
2351 exist in the archive. @xref{update}.
2355 @node Option Summary
2356 @subsection @command{tar} Options
2360 @opsummary{absolute-names}
2361 @item --absolute-names
2364 Normally when creating an archive, @command{tar} strips an initial
2365 @samp{/} from member names. This option disables that behavior.
2368 @opsummary{after-date}
2371 (See @option{--newer}, @pxref{after})
2373 @opsummary{anchored}
2375 A pattern must match an initial subsequence of the name's components.
2376 @xref{controlling pattern-matching}.
2378 @opsummary{atime-preserve}
2379 @item --atime-preserve
2380 @itemx --atime-preserve=replace
2381 @itemx --atime-preserve=system
2383 Attempt to preserve the access time of files when reading them. This
2384 option currently is effective only on files that you own, unless you
2385 have superuser privileges.
2387 @option{--atime-preserve=replace} remembers the access time of a file
2388 before reading it, and then restores the access time afterwards. This
2389 may cause problems if other programs are reading the file at the same
2390 time, as the times of their accesses will be lost. On most platforms
2391 restoring the access time also requires @command{tar} to restore the
2392 data modification time too, so this option may also cause problems if
2393 other programs are writing the file at the same time. (Tar attempts
2394 to detect this situation, but cannot do so reliably due to race
2395 conditions.) Worse, on most platforms restoring the access time also
2396 updates the status change time, which means that this option is
2397 incompatible with incremental backups.
2399 @option{--atime-preserve=system} avoids changing time stamps on files,
2400 without interfering with time stamp updates
2401 caused by other programs, so it works better with incremental backups.
2402 However, it requires a special @code{O_NOATIME} option from the
2403 underlying operating and file system implementation, and it also requires
2404 that searching directories does not update their access times. As of
2405 this writing (November 2005) this works only with Linux, and only with
2406 Linux kernels 2.6.8 and later. Worse, there is currently no reliable
2407 way to know whether this feature actually works. Sometimes
2408 @command{tar} knows that it does not work, and if you use
2409 @option{--atime-preserve=system} then @command{tar} complains and
2410 exits right away. But other times @command{tar} might think that the
2411 option works when it actually does not.
2413 Currently @option{--atime-preserve} with no operand defaults to
2414 @option{--atime-preserve=replace}, but this may change in the future
2415 as support for @option{--atime-preserve=system} improves.
2417 If your operating system does not support
2418 @option{--atime-preserve=@-system}, you might be able to preserve access
2419 times reliably by by using the @command{mount} command. For example,
2420 you can mount the file system read-only, or access the file system via
2421 a read-only loopback mount, or use the @samp{noatime} mount option
2422 available on some systems. However, mounting typically requires
2423 superuser privileges and can be a pain to manage.
2425 @opsummary{auto-compress}
2426 @item --auto-compress
2429 During a @option{--create} operation, enables automatic compressed
2430 format recognition based on the archive suffix. The effect of this
2431 option is cancelled by @option{--no-auto-compress}. @xref{gzip}.
2434 @item --backup=@var{backup-type}
2436 Rather than deleting files from the file system, @command{tar} will
2437 back them up using simple or numbered backups, depending upon
2438 @var{backup-type}. @xref{backup}.
2440 @opsummary{block-number}
2441 @item --block-number
2444 With this option present, @command{tar} prints error messages for read errors
2445 with the block number in the archive file. @xref{block-number}.
2447 @opsummary{blocking-factor}
2448 @item --blocking-factor=@var{blocking}
2449 @itemx -b @var{blocking}
2451 Sets the blocking factor @command{tar} uses to @var{blocking} x 512 bytes per
2452 record. @xref{Blocking Factor}.
2458 This option tells @command{tar} to read or write archives through
2459 @code{bzip2}. @xref{gzip}.
2461 @opsummary{check-device}
2462 @item --check-device
2463 Check device numbers when creating a list of modified files for
2464 incremental archiving. This is the default. @xref{device numbers},
2465 for a detailed description.
2467 @opsummary{checkpoint}
2468 @item --checkpoint[=@var{number}]
2470 This option directs @command{tar} to print periodic checkpoint
2471 messages as it reads through the archive. It is intended for when you
2472 want a visual indication that @command{tar} is still running, but
2473 don't want to see @option{--verbose} output. You can also instruct
2474 @command{tar} to execute a list of actions on each checkpoint, see
2475 @option{--checkpoint-action} below. For a detailed description, see
2478 @opsummary{checkpoint-action}
2479 @item --checkpoint-action=@var{action}
2480 Instruct @command{tar} to execute an action upon hitting a
2481 breakpoint. Here we give only a brief outline. @xref{checkpoints},
2482 for a complete description.
2484 The @var{action} argument can be one of the following:
2488 Produce an audible bell on the console.
2492 Print a single dot on the standard listing stream.
2495 Display a textual message on the standard error, with the status and
2496 number of the checkpoint. This is the default.
2498 @item echo=@var{string}
2499 Display @var{string} on the standard error. Before output, the string
2500 is subject to meta-character expansion.
2502 @item exec=@var{command}
2503 Execute the given @var{command}.
2505 @item sleep=@var{time}
2506 Wait for @var{time} seconds.
2508 @item ttyout=@var{string}
2509 Output @var{string} on the current console (@file{/dev/tty}).
2512 Several @option{--checkpoint-action} options can be specified. The
2513 supplied actions will be executed in order of their appearance in the
2516 Using @option{--checkpoint-action} without @option{--checkpoint}
2517 assumes default checkpoint frequency of one checkpoint per 10 records.
2519 @opsummary{check-links}
2522 If this option was given, @command{tar} will check the number of links
2523 dumped for each processed file. If this number does not match the
2524 total number of hard links for the file, a warning message will be
2525 output @footnote{Earlier versions of @GNUTAR{} understood @option{-l} as a
2526 synonym for @option{--one-file-system}. The current semantics, which
2527 complies to UNIX98, was introduced with version
2528 1.15.91. @xref{Changes}, for more information.}.
2532 @opsummary{compress}
2533 @opsummary{uncompress}
2538 @command{tar} will use the @command{compress} program when reading or
2539 writing the archive. This allows you to directly act on archives
2540 while saving space. @xref{gzip}.
2542 @opsummary{confirmation}
2543 @item --confirmation
2545 (See @option{--interactive}.) @xref{interactive}.
2547 @opsummary{delay-directory-restore}
2548 @item --delay-directory-restore
2550 Delay setting modification times and permissions of extracted
2551 directories until the end of extraction. @xref{Directory Modification Times and Permissions}.
2553 @opsummary{dereference}
2557 When creating a @command{tar} archive, @command{tar} will archive the
2558 file that a symbolic link points to, rather than archiving the
2559 symlink. @xref{dereference}.
2561 @opsummary{directory}
2562 @item --directory=@var{dir}
2565 When this option is specified, @command{tar} will change its current directory
2566 to @var{dir} before performing any operations. When this option is used
2567 during archive creation, it is order sensitive. @xref{directory}.
2570 @item --exclude=@var{pattern}
2572 When performing operations, @command{tar} will skip files that match
2573 @var{pattern}. @xref{exclude}.
2575 @opsummary{exclude-backups}
2576 @item --exclude-backups
2577 Exclude backup and lock files. @xref{exclude,, exclude-backups}.
2579 @opsummary{exclude-from}
2580 @item --exclude-from=@var{file}
2581 @itemx -X @var{file}
2583 Similar to @option{--exclude}, except @command{tar} will use the list of
2584 patterns in the file @var{file}. @xref{exclude}.
2586 @opsummary{exclude-caches}
2587 @item --exclude-caches
2589 Exclude from dump any directory containing a valid cache directory
2590 tag file, but still dump the directory node and the tag file itself.
2592 @xref{exclude,, exclude-caches}.
2594 @opsummary{exclude-caches-under}
2595 @item --exclude-caches-under
2597 Exclude from dump any directory containing a valid cache directory
2598 tag file, but still dump the directory node itself.
2602 @opsummary{exclude-caches-all}
2603 @item --exclude-caches-all
2605 Exclude from dump any directory containing a valid cache directory
2606 tag file. @xref{exclude}.
2608 @opsummary{exclude-tag}
2609 @item --exclude-tag=@var{file}
2611 Exclude from dump any directory containing file named @var{file}, but
2612 dump the directory node and @var{file} itself. @xref{exclude,, exclude-tag}.
2614 @opsummary{exclude-tag-under}
2615 @item --exclude-tag-under=@var{file}
2617 Exclude from dump the contents of any directory containing file
2618 named @var{file}, but dump the directory node itself. @xref{exclude,,
2621 @opsummary{exclude-tag-all}
2622 @item --exclude-tag-all=@var{file}
2624 Exclude from dump any directory containing file named @var{file}.
2625 @xref{exclude,,exclude-tag-all}.
2627 @opsummary{exclude-vcs}
2630 Exclude from dump directories and files, that are internal for some
2631 widely used version control systems.
2633 @xref{exclude,,exclude-vcs}.
2636 @item --file=@var{archive}
2637 @itemx -f @var{archive}
2639 @command{tar} will use the file @var{archive} as the @command{tar} archive it
2640 performs operations on, rather than @command{tar}'s compilation dependent
2641 default. @xref{file tutorial}.
2643 @opsummary{files-from}
2644 @item --files-from=@var{file}
2645 @itemx -T @var{file}
2647 @command{tar} will use the contents of @var{file} as a list of archive members
2648 or files to operate on, in addition to those specified on the
2649 command-line. @xref{files}.
2651 @opsummary{force-local}
2654 Forces @command{tar} to interpret the file name given to @option{--file}
2655 as a local file, even if it looks like a remote tape drive name.
2656 @xref{local and remote archives}.
2659 @item --format=@var{format}
2660 @itemx -H @var{format}
2662 Selects output archive format. @var{Format} may be one of the
2667 Creates an archive that is compatible with Unix V7 @command{tar}.
2670 Creates an archive that is compatible with GNU @command{tar} version
2674 Creates archive in GNU tar 1.13 format. Basically it is the same as
2675 @samp{oldgnu} with the only difference in the way it handles long
2679 Creates a @acronym{POSIX.1-1988} compatible archive.
2682 Creates a @acronym{POSIX.1-2001 archive}.
2686 @xref{Formats}, for a detailed discussion of these formats.
2689 @item --group=@var{group}
2691 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
2692 rather than the group from the source file. @var{group} is first decoded
2693 as a group symbolic name, but if this interpretation fails, it has to be
2694 a decimal numeric group @acronym{ID}. @xref{override}.
2696 Also see the comments for the @option{--owner=@var{user}} option.
2706 This option tells @command{tar} to read or write archives through
2707 @command{gzip}, allowing @command{tar} to directly operate on several
2708 kinds of compressed archives transparently. @xref{gzip}.
2710 @opsummary{hard-dereference}
2711 @item --hard-dereference
2712 When creating an archive, dereference hard links and store the files
2713 they refer to, instead of creating usual hard link members.
2721 @command{tar} will print out a short message summarizing the operations and
2722 options to @command{tar} and exit. @xref{help}.
2724 @opsummary{ignore-case}
2726 Ignore case when matching member or file names with
2727 patterns. @xref{controlling pattern-matching}.
2729 @opsummary{ignore-command-error}
2730 @item --ignore-command-error
2731 Ignore exit codes of subprocesses. @xref{Writing to an External Program}.
2733 @opsummary{ignore-failed-read}
2734 @item --ignore-failed-read
2736 Do not exit unsuccessfully merely because an unreadable file was encountered.
2739 @opsummary{ignore-zeros}
2740 @item --ignore-zeros
2743 With this option, @command{tar} will ignore zeroed blocks in the
2744 archive, which normally signals EOF. @xref{Reading}.
2746 @opsummary{incremental}
2750 Informs @command{tar} that it is working with an old
2751 @acronym{GNU}-format incremental backup archive. It is intended
2752 primarily for backwards compatibility only. @xref{Incremental Dumps},
2753 for a detailed discussion of incremental archives.
2755 @opsummary{index-file}
2756 @item --index-file=@var{file}
2758 Send verbose output to @var{file} instead of to standard output.
2760 @opsummary{info-script}
2761 @opsummary{new-volume-script}
2762 @item --info-script=@var{script-file}
2763 @itemx --new-volume-script=@var{script-file}
2764 @itemx -F @var{script-file}
2766 When @command{tar} is performing multi-tape backups, @var{script-file} is run
2767 at the end of each tape. If @var{script-file} exits with nonzero status,
2768 @command{tar} fails immediately. @xref{info-script}, for a detailed
2769 discussion of @var{script-file}.
2771 @opsummary{interactive}
2773 @itemx --confirmation
2776 Specifies that @command{tar} should ask the user for confirmation before
2777 performing potentially destructive options, such as overwriting files.
2780 @opsummary{keep-newer-files}
2781 @item --keep-newer-files
2783 Do not replace existing files that are newer than their archive copies
2784 when extracting files from an archive.
2786 @opsummary{keep-old-files}
2787 @item --keep-old-files
2790 Do not overwrite existing files when extracting files from an archive.
2791 @xref{Keep Old Files}.
2794 @item --label=@var{name}
2795 @itemx -V @var{name}
2797 When creating an archive, instructs @command{tar} to write @var{name}
2798 as a name record in the archive. When extracting or listing archives,
2799 @command{tar} will only operate on archives that have a label matching
2800 the pattern specified in @var{name}. @xref{Tape Files}.
2803 @item --level=@var{n}
2804 Force incremental backup of level @var{n}. As of @GNUTAR version
2805 @value{VERSION}, the option @option{--level=0} truncates the snapshot
2806 file, thereby forcing the level 0 dump. Other values of @var{n} are
2807 effectively ignored. @xref{--level=0}, for details and examples.
2809 The use of this option is valid only in conjunction with the
2810 @option{--listed-incremental} option. @xref{Incremental Dumps},
2811 for a detailed description.
2813 @opsummary{listed-incremental}
2814 @item --listed-incremental=@var{snapshot-file}
2815 @itemx -g @var{snapshot-file}
2817 During a @option{--create} operation, specifies that the archive that
2818 @command{tar} creates is a new @acronym{GNU}-format incremental
2819 backup, using @var{snapshot-file} to determine which files to backup.
2820 With other operations, informs @command{tar} that the archive is in
2821 incremental format. @xref{Incremental Dumps}.
2826 This option tells @command{tar} to read or write archives through
2827 @command{lzip}. @xref{gzip}.
2832 This option tells @command{tar} to read or write archives through
2833 @command{lzma}. @xref{gzip}.
2837 This option tells @command{tar} to read or write archives through
2838 @command{lzop}. @xref{gzip}.
2841 @item --mode=@var{permissions}
2843 When adding files to an archive, @command{tar} will use
2844 @var{permissions} for the archive members, rather than the permissions
2845 from the files. @var{permissions} can be specified either as an octal
2846 number or as symbolic permissions, like with
2847 @command{chmod}. @xref{override}.
2850 @item --mtime=@var{date}
2852 When adding files to an archive, @command{tar} will use @var{date} as
2853 the modification time of members when creating archives, instead of
2854 their actual modification times. The value of @var{date} can be
2855 either a textual date representation (@pxref{Date input formats}) or a
2856 name of the existing file, starting with @samp{/} or @samp{.}. In the
2857 latter case, the modification time of that file is used. @xref{override}.
2859 @opsummary{multi-volume}
2860 @item --multi-volume
2863 Informs @command{tar} that it should create or otherwise operate on a
2864 multi-volume @command{tar} archive. @xref{Using Multiple Tapes}.
2866 @opsummary{new-volume-script}
2867 @item --new-volume-script
2872 @item --newer=@var{date}
2873 @itemx --after-date=@var{date}
2876 When creating an archive, @command{tar} will only add files that have changed
2877 since @var{date}. If @var{date} begins with @samp{/} or @samp{.}, it
2878 is taken to be the name of a file whose data modification time specifies
2879 the date. @xref{after}.
2881 @opsummary{newer-mtime}
2882 @item --newer-mtime=@var{date}
2884 Like @option{--newer}, but add only files whose
2885 contents have changed (as opposed to just @option{--newer}, which will
2886 also back up files for which any status information has
2887 changed). @xref{after}.
2889 @opsummary{no-anchored}
2891 An exclude pattern can match any subsequence of the name's components.
2892 @xref{controlling pattern-matching}.
2894 @opsummary{no-auto-compress}
2895 @item --no-auto-compress
2897 Disables automatic compressed format recognition based on the archive
2898 suffix. @xref{--auto-compress}. @xref{gzip}.
2900 @opsummary{no-check-device}
2901 @item --no-check-device
2902 Do not check device numbers when creating a list of modified files
2903 for incremental archiving. @xref{device numbers}, for
2904 a detailed description.
2906 @opsummary{no-delay-directory-restore}
2907 @item --no-delay-directory-restore
2909 Modification times and permissions of extracted
2910 directories are set when all files from this directory have been
2911 extracted. This is the default.
2912 @xref{Directory Modification Times and Permissions}.
2914 @opsummary{no-ignore-case}
2915 @item --no-ignore-case
2916 Use case-sensitive matching.
2917 @xref{controlling pattern-matching}.
2919 @opsummary{no-ignore-command-error}
2920 @item --no-ignore-command-error
2921 Print warnings about subprocesses that terminated with a nonzero exit
2922 code. @xref{Writing to an External Program}.
2927 If the @option{--null} option was given previously, this option
2928 cancels its effect, so that any following @option{--files-from}
2929 options will expect their file lists to be newline-terminated.
2931 @opsummary{no-overwrite-dir}
2932 @item --no-overwrite-dir
2934 Preserve metadata of existing directories when extracting files
2935 from an archive. @xref{Overwrite Old Files}.
2937 @opsummary{no-quote-chars}
2938 @item --no-quote-chars=@var{string}
2939 Remove characters listed in @var{string} from the list of quoted
2940 characters set by the previous @option{--quote-chars} option
2941 (@pxref{quoting styles}).
2943 @opsummary{no-recursion}
2944 @item --no-recursion
2946 With this option, @command{tar} will not recurse into directories.
2949 @opsummary{no-same-owner}
2950 @item --no-same-owner
2953 When extracting an archive, do not attempt to preserve the owner
2954 specified in the @command{tar} archive. This the default behavior
2957 @opsummary{no-same-permissions}
2958 @item --no-same-permissions
2960 When extracting an archive, subtract the user's umask from files from
2961 the permissions specified in the archive. This is the default behavior
2967 The archive media does not support seeks to arbitrary
2968 locations. Usually @command{tar} determines automatically whether
2969 the archive can be seeked or not. Use this option to disable this
2972 @opsummary{no-unquote}
2974 Treat all input file or member names literally, do not interpret
2975 escape sequences. @xref{input name quoting}.
2977 @opsummary{no-wildcards}
2978 @item --no-wildcards
2979 Do not use wildcards.
2980 @xref{controlling pattern-matching}.
2982 @opsummary{no-wildcards-match-slash}
2983 @item --no-wildcards-match-slash
2984 Wildcards do not match @samp{/}.
2985 @xref{controlling pattern-matching}.
2990 When @command{tar} is using the @option{--files-from} option, this option
2991 instructs @command{tar} to expect file names terminated with @acronym{NUL}, so
2992 @command{tar} can correctly work with file names that contain newlines.
2995 @opsummary{numeric-owner}
2996 @item --numeric-owner
2998 This option will notify @command{tar} that it should use numeric user
2999 and group IDs when creating a @command{tar} file, rather than names.
3003 The function of this option depends on the action @command{tar} is
3004 performing. When extracting files, @option{-o} is a synonym for
3005 @option{--no-same-owner}, i.e., it prevents @command{tar} from
3006 restoring ownership of files being extracted.
3008 When creating an archive, it is a synonym for
3009 @option{--old-archive}. This behavior is for compatibility
3010 with previous versions of @GNUTAR{}, and will be
3011 removed in future releases.
3013 @xref{Changes}, for more information.
3015 @opsummary{occurrence}
3016 @item --occurrence[=@var{number}]
3018 This option can be used in conjunction with one of the subcommands
3019 @option{--delete}, @option{--diff}, @option{--extract} or
3020 @option{--list} when a list of files is given either on the command
3021 line or via @option{-T} option.
3023 This option instructs @command{tar} to process only the @var{number}th
3024 occurrence of each named file. @var{Number} defaults to 1, so
3027 tar -x -f archive.tar --occurrence filename
3031 will extract the first occurrence of the member @file{filename} from @file{archive.tar}
3032 and will terminate without scanning to the end of the archive.
3034 @opsummary{old-archive}
3036 Synonym for @option{--format=v7}.
3038 @opsummary{one-file-system}
3039 @item --one-file-system
3040 Used when creating an archive. Prevents @command{tar} from recursing into
3041 directories that are on different file systems from the current
3044 @opsummary{overwrite}
3047 Overwrite existing files and directory metadata when extracting files
3048 from an archive. @xref{Overwrite Old Files}.
3050 @opsummary{overwrite-dir}
3051 @item --overwrite-dir
3053 Overwrite the metadata of existing directories when extracting files
3054 from an archive. @xref{Overwrite Old Files}.
3057 @item --owner=@var{user}
3059 Specifies that @command{tar} should use @var{user} as the owner of members
3060 when creating archives, instead of the user associated with the source
3061 file. @var{user} is first decoded as a user symbolic name, but if
3062 this interpretation fails, it has to be a decimal numeric user @acronym{ID}.
3065 This option does not affect extraction from archives.
3067 @opsummary{pax-option}
3068 @item --pax-option=@var{keyword-list}
3069 This option enables creation of the archive in @acronym{POSIX.1-2001}
3070 format (@pxref{posix}) and modifies the way @command{tar} handles the
3071 extended header keywords. @var{Keyword-list} is a comma-separated
3072 list of keyword options. @xref{PAX keywords}, for a detailed
3075 @opsummary{portability}
3077 @itemx --old-archive
3078 Synonym for @option{--format=v7}.
3082 Same as @option{--format=posix}.
3084 @opsummary{preserve}
3087 Synonymous with specifying both @option{--preserve-permissions} and
3088 @option{--same-order}. @xref{Setting Access Permissions}.
3090 @opsummary{preserve-order}
3091 @item --preserve-order
3093 (See @option{--same-order}; @pxref{Reading}.)
3095 @opsummary{preserve-permissions}
3096 @opsummary{same-permissions}
3097 @item --preserve-permissions
3098 @itemx --same-permissions
3101 When @command{tar} is extracting an archive, it normally subtracts the
3102 users' umask from the permissions specified in the archive and uses
3103 that number as the permissions to create the destination file.
3104 Specifying this option instructs @command{tar} that it should use the
3105 permissions directly from the archive. @xref{Setting Access Permissions}.
3107 @opsummary{quote-chars}
3108 @item --quote-chars=@var{string}
3109 Always quote characters from @var{string}, even if the selected
3110 quoting style would not quote them (@pxref{quoting styles}).
3112 @opsummary{quoting-style}
3113 @item --quoting-style=@var{style}
3114 Set quoting style to use when printing member and file names
3115 (@pxref{quoting styles}). Valid @var{style} values are:
3116 @code{literal}, @code{shell}, @code{shell-always}, @code{c},
3117 @code{escape}, @code{locale}, and @code{clocale}. Default quoting
3118 style is @code{escape}, unless overridden while configuring the
3121 @opsummary{read-full-records}
3122 @item --read-full-records
3125 Specifies that @command{tar} should reblock its input, for reading
3126 from pipes on systems with buggy implementations. @xref{Reading}.
3128 @opsummary{record-size}
3129 @item --record-size=@var{size}
3131 Instructs @command{tar} to use @var{size} bytes per record when accessing the
3132 archive. @xref{Blocking Factor}.
3134 @opsummary{recursion}
3137 With this option, @command{tar} recurses into directories (default).
3140 @opsummary{recursive-unlink}
3141 @item --recursive-unlink
3144 directory hierarchies before extracting directories of the same name
3145 from the archive. @xref{Recursive Unlink}.
3147 @opsummary{remove-files}
3148 @item --remove-files
3150 Directs @command{tar} to remove the source file from the file system after
3151 appending it to an archive. @xref{remove files}.
3153 @opsummary{restrict}
3156 Disable use of some potentially harmful @command{tar} options.
3157 Currently this option disables shell invocation from multi-volume menu
3158 (@pxref{Using Multiple Tapes}).
3160 @opsummary{rmt-command}
3161 @item --rmt-command=@var{cmd}
3163 Notifies @command{tar} that it should use @var{cmd} instead of
3164 the default @file{/usr/libexec/rmt} (@pxref{Remote Tape Server}).
3166 @opsummary{rsh-command}
3167 @item --rsh-command=@var{cmd}
3169 Notifies @command{tar} that is should use @var{cmd} to communicate with remote
3170 devices. @xref{Device}.
3172 @opsummary{same-order}
3174 @itemx --preserve-order
3177 This option is an optimization for @command{tar} when running on machines with
3178 small amounts of memory. It informs @command{tar} that the list of file
3179 arguments has already been sorted to match the order of files in the
3180 archive. @xref{Reading}.
3182 @opsummary{same-owner}
3185 When extracting an archive, @command{tar} will attempt to preserve the owner
3186 specified in the @command{tar} archive with this option present.
3187 This is the default behavior for the superuser; this option has an
3188 effect only for ordinary users. @xref{Attributes}.
3190 @opsummary{same-permissions}
3191 @item --same-permissions
3193 (See @option{--preserve-permissions}; @pxref{Setting Access Permissions}.)
3199 Assume that the archive media supports seeks to arbitrary
3200 locations. Usually @command{tar} determines automatically whether
3201 the archive can be seeked or not. This option is intended for use
3202 in cases when such recognition fails. It takes effect only if the
3203 archive is open for reading (e.g. with @option{--list} or
3204 @option{--extract} options).
3206 @opsummary{show-defaults}
3207 @item --show-defaults
3209 Displays the default options used by @command{tar} and exits
3210 successfully. This option is intended for use in shell scripts.
3211 Here is an example of what you can see using this option:
3214 $ tar --show-defaults
3215 --format=gnu -f- -b20 --quoting-style=escape \
3216 --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
3219 @opsummary{show-omitted-dirs}
3220 @item --show-omitted-dirs
3222 Instructs @command{tar} to mention the directories it is skipping when
3223 operating on a @command{tar} archive. @xref{show-omitted-dirs}.
3225 @opsummary{show-transformed-names}
3226 @opsummary{show-stored-names}
3227 @item --show-transformed-names
3228 @itemx --show-stored-names
3230 Display file or member names after applying any transformations
3231 (@pxref{transform}). In particular, when used in conjunction with one of
3232 the archive creation operations it instructs @command{tar} to list the
3233 member names stored in the archive, as opposed to the actual file
3234 names. @xref{listing member and file names}.
3240 Invokes a @acronym{GNU} extension when adding files to an archive that handles
3241 sparse files efficiently. @xref{sparse}.
3243 @opsummary{sparse-version}
3244 @item --sparse-version=@var{version}
3246 Specifies the @dfn{format version} to use when archiving sparse
3247 files. Implies @option{--sparse}. @xref{sparse}. For the description
3248 of the supported sparse formats, @xref{Sparse Formats}.
3250 @opsummary{starting-file}
3251 @item --starting-file=@var{name}
3252 @itemx -K @var{name}
3254 This option affects extraction only; @command{tar} will skip extracting
3255 files in the archive until it finds one that matches @var{name}.
3258 @opsummary{strip-components}
3259 @item --strip-components=@var{number}
3260 Strip given @var{number} of leading components from file names before
3261 extraction. For example, if archive @file{archive.tar} contained
3262 @file{/some/file/name}, then running
3265 tar --extract --file archive.tar --strip-components=2
3269 would extract this file to file @file{name}.
3271 @opsummary{suffix}, summary
3272 @item --suffix=@var{suffix}
3274 Alters the suffix @command{tar} uses when backing up files from the default
3275 @samp{~}. @xref{backup}.
3277 @opsummary{tape-length}
3278 @item --tape-length=@var{num}
3281 Specifies the length of tapes that @command{tar} is writing as being
3282 @w{@var{num} x 1024} bytes long. @xref{Using Multiple Tapes}.
3284 @opsummary{test-label}
3287 Reads the volume label. If an argument is specified, test whether it
3288 matches the volume label. @xref{--test-label option}.
3290 @opsummary{to-command}
3291 @item --to-command=@var{command}
3293 During extraction @command{tar} will pipe extracted files to the
3294 standard input of @var{command}. @xref{Writing to an External Program}.
3296 @opsummary{to-stdout}
3300 During extraction, @command{tar} will extract files to stdout rather
3301 than to the file system. @xref{Writing to Standard Output}.
3304 @item --totals[=@var{signo}]
3306 Displays the total number of bytes transferred when processing an
3307 archive. If an argument is given, these data are displayed on
3308 request, when signal @var{signo} is delivered to @command{tar}.
3315 Sets the data modification time of extracted files to the extraction time,
3316 rather than the data modification time stored in the archive.
3317 @xref{Data Modification Times}.
3319 @opsummary{transform}
3321 @item --transform=@var{sed-expr}
3322 @itemx --xform=@var{sed-expr}
3323 Transform file or member names using @command{sed} replacement expression
3324 @var{sed-expr}. For example,
3327 $ @kbd{tar cf archive.tar --transform 's,^\./,usr/,' .}
3331 will add to @file{archive} files from the current working directory,
3332 replacing initial @samp{./} prefix with @samp{usr/}. For the detailed
3333 discussion, @xref{transform}.
3335 To see transformed member names in verbose listings, use
3336 @option{--show-transformed-names} option
3337 (@pxref{show-transformed-names}).
3339 @opsummary{uncompress}
3342 (See @option{--compress}. @pxref{gzip})
3347 (See @option{--gzip}. @pxref{gzip})
3349 @opsummary{unlink-first}
3350 @item --unlink-first
3353 Directs @command{tar} to remove the corresponding file from the file
3354 system before extracting it from the archive. @xref{Unlink First}.
3358 Enable unquoting input file or member names (default). @xref{input
3361 @opsummary{use-compress-program}
3362 @item --use-compress-program=@var{prog}
3363 @itemx -I=@var{prog}
3365 Instructs @command{tar} to access the archive through @var{prog}, which is
3366 presumed to be a compression program of some sort. @xref{gzip}.
3371 Display file modification dates in @acronym{UTC}. This option implies
3378 Specifies that @command{tar} should be more verbose about the
3379 operations it is performing. This option can be specified multiple
3380 times for some operations to increase the amount of information displayed.
3387 Verifies that the archive was correctly written when creating an
3388 archive. @xref{verify}.
3393 Print information about the program's name, version, origin and legal
3394 status, all on standard output, and then exit successfully.
3397 @opsummary{volno-file}
3398 @item --volno-file=@var{file}
3400 Used in conjunction with @option{--multi-volume}. @command{tar} will
3401 keep track of which volume of a multi-volume archive it is working in
3402 @var{file}. @xref{volno-file}.
3405 @item --warning=@var{keyword}
3407 Enable or disable warning messages identified by @var{keyword}. The
3408 messages are suppressed if @var{keyword} is prefixed with @samp{no-}.
3411 @opsummary{wildcards}
3413 Use wildcards when matching member names with patterns.
3414 @xref{controlling pattern-matching}.
3416 @opsummary{wildcards-match-slash}
3417 @item --wildcards-match-slash
3418 Wildcards match @samp{/}.
3419 @xref{controlling pattern-matching}.
3424 Use @command{xz} for compressing or decompressing the archives. @xref{gzip}.
3428 @node Short Option Summary
3429 @subsection Short Options Cross Reference
3431 Here is an alphabetized list of all of the short option forms, matching
3432 them with the equivalent long option.
3434 @multitable @columnfractions 0.20 0.80
3435 @headitem Short Option @tab Reference
3437 @item -A @tab @ref{--concatenate}.
3439 @item -B @tab @ref{--read-full-records}.
3441 @item -C @tab @ref{--directory}.
3443 @item -F @tab @ref{--info-script}.
3445 @item -G @tab @ref{--incremental}.
3447 @item -J @tab @ref{--xz}.
3449 @item -K @tab @ref{--starting-file}.
3451 @item -L @tab @ref{--tape-length}.
3453 @item -M @tab @ref{--multi-volume}.
3455 @item -N @tab @ref{--newer}.
3457 @item -O @tab @ref{--to-stdout}.
3459 @item -P @tab @ref{--absolute-names}.
3461 @item -R @tab @ref{--block-number}.
3463 @item -S @tab @ref{--sparse}.
3465 @item -T @tab @ref{--files-from}.
3467 @item -U @tab @ref{--unlink-first}.
3469 @item -V @tab @ref{--label}.
3471 @item -W @tab @ref{--verify}.
3473 @item -X @tab @ref{--exclude-from}.
3475 @item -Z @tab @ref{--compress}.
3477 @item -b @tab @ref{--blocking-factor}.
3479 @item -c @tab @ref{--create}.
3481 @item -d @tab @ref{--compare}.
3483 @item -f @tab @ref{--file}.
3485 @item -g @tab @ref{--listed-incremental}.
3487 @item -h @tab @ref{--dereference}.
3489 @item -i @tab @ref{--ignore-zeros}.
3491 @item -j @tab @ref{--bzip2}.
3493 @item -k @tab @ref{--keep-old-files}.
3495 @item -l @tab @ref{--check-links}.
3497 @item -m @tab @ref{--touch}.
3499 @item -o @tab When creating, @ref{--no-same-owner}, when extracting ---
3500 @ref{--portability}.
3502 The latter usage is deprecated. It is retained for compatibility with
3503 the earlier versions of @GNUTAR{}. In future releases
3504 @option{-o} will be equivalent to @option{--no-same-owner} only.
3506 @item -p @tab @ref{--preserve-permissions}.
3508 @item -r @tab @ref{--append}.
3510 @item -s @tab @ref{--same-order}.
3512 @item -t @tab @ref{--list}.
3514 @item -u @tab @ref{--update}.
3516 @item -v @tab @ref{--verbose}.
3518 @item -w @tab @ref{--interactive}.
3520 @item -x @tab @ref{--extract}.
3522 @item -z @tab @ref{--gzip}.
3527 @section @GNUTAR{} documentation
3529 @cindex Getting program version number
3531 @cindex Version of the @command{tar} program
3532 Being careful, the first thing is really checking that you are using
3533 @GNUTAR{}, indeed. The @option{--version} option
3534 causes @command{tar} to print information about its name, version,
3535 origin and legal status, all on standard output, and then exit
3536 successfully. For example, @w{@samp{tar --version}} might print:
3539 tar (GNU tar) @value{VERSION}
3540 Copyright (C) 2008 Free Software Foundation, Inc.
3541 This is free software. You may redistribute copies of it under the terms
3542 of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
3543 There is NO WARRANTY, to the extent permitted by law.
3545 Written by John Gilmore and Jay Fenlason.
3549 The first occurrence of @samp{tar} in the result above is the program
3550 name in the package (for example, @command{rmt} is another program),
3551 while the second occurrence of @samp{tar} is the name of the package
3552 itself, containing possibly many programs. The package is currently
3553 named @samp{tar}, after the name of the main program it
3554 contains@footnote{There are plans to merge the @command{cpio} and
3555 @command{tar} packages into a single one which would be called
3556 @code{paxutils}. So, who knows if, one of this days, the
3557 @option{--version} would not output @w{@samp{tar (@acronym{GNU}
3560 @cindex Obtaining help
3561 @cindex Listing all @command{tar} options
3562 @xopindex{help, introduction}
3563 Another thing you might want to do is checking the spelling or meaning
3564 of some particular @command{tar} option, without resorting to this
3565 manual, for once you have carefully read it. @GNUTAR{}
3566 has a short help feature, triggerable through the
3567 @option{--help} option. By using this option, @command{tar} will
3568 print a usage message listing all available options on standard
3569 output, then exit successfully, without doing anything else and
3570 ignoring all other options. Even if this is only a brief summary, it
3571 may be several screens long. So, if you are not using some kind of
3572 scrollable window, you might prefer to use something like:
3575 $ @kbd{tar --help | less}
3579 presuming, here, that you like using @command{less} for a pager. Other
3580 popular pagers are @command{more} and @command{pg}. If you know about some
3581 @var{keyword} which interests you and do not want to read all the
3582 @option{--help} output, another common idiom is doing:
3585 tar --help | grep @var{keyword}
3589 for getting only the pertinent lines. Notice, however, that some
3590 @command{tar} options have long description lines and the above
3591 command will list only the first of them.
3593 The exact look of the option summary displayed by @kbd{tar --help} is
3594 configurable. @xref{Configuring Help Summary}, for a detailed description.
3597 If you only wish to check the spelling of an option, running @kbd{tar
3598 --usage} may be a better choice. This will display a terse list of
3599 @command{tar} option without accompanying explanations.
3601 The short help output is quite succinct, and you might have to get
3602 back to the full documentation for precise points. If you are reading
3603 this paragraph, you already have the @command{tar} manual in some
3604 form. This manual is available in a variety of forms from
3605 @url{http://www.gnu.org/software/tar/manual}. It may be printed out of the @GNUTAR{}
3606 distribution, provided you have @TeX{} already installed somewhere,
3607 and a laser printer around. Just configure the distribution, execute
3608 the command @w{@samp{make dvi}}, then print @file{doc/tar.dvi} the
3609 usual way (contact your local guru to know how). If @GNUTAR{}
3610 has been conveniently installed at your place, this
3611 manual is also available in interactive, hypertextual form as an Info
3612 file. Just call @w{@samp{info tar}} or, if you do not have the
3613 @command{info} program handy, use the Info reader provided within
3614 @acronym{GNU} Emacs, calling @samp{tar} from the main Info menu.
3616 There is currently no @code{man} page for @GNUTAR{}.
3617 If you observe such a @code{man} page on the system you are running,
3618 either it does not belong to @GNUTAR{}, or it has not
3619 been produced by @acronym{GNU}. Some package maintainers convert
3620 @kbd{tar --help} output to a man page, using @command{help2man}. In
3621 any case, please bear in mind that the authoritative source of
3622 information about @GNUTAR{} is this Texinfo documentation.
3625 @section Obtaining @GNUTAR{} default values
3627 @opindex show-defaults
3628 @GNUTAR{} has some predefined defaults that are used when you do not
3629 explicitly specify another values. To obtain a list of such
3630 defaults, use @option{--show-defaults} option. This will output the
3631 values in the form of @command{tar} command line options:
3635 @kbd{tar --show-defaults}
3636 --format=gnu -f- -b20 --quoting-style=escape
3637 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
3642 Notice, that this option outputs only one line. The example output above
3643 has been split to fit page boundaries.
3646 The above output shows that this version of @GNUTAR{} defaults to
3647 using @samp{gnu} archive format (@pxref{Formats}), it uses standard
3648 output as the archive, if no @option{--file} option has been given
3649 (@pxref{file tutorial}), the default blocking factor is 20
3650 (@pxref{Blocking Factor}). It also shows the default locations where
3651 @command{tar} will look for @command{rmt} and @command{rsh} binaries.
3654 @section Checking @command{tar} progress
3656 Typically, @command{tar} performs most operations without reporting any
3657 information to the user except error messages. When using @command{tar}
3658 with many options, particularly ones with complicated or
3659 difficult-to-predict behavior, it is possible to make serious mistakes.
3660 @command{tar} provides several options that make observing @command{tar}
3661 easier. These options cause @command{tar} to print information as it
3662 progresses in its job, and you might want to use them just for being
3663 more careful about what is going on, or merely for entertaining
3664 yourself. If you have encountered a problem when operating on an
3665 archive, however, you may need more information than just an error
3666 message in order to solve the problem. The following options can be
3667 helpful diagnostic tools.
3669 @cindex Verbose operation
3671 Normally, the @option{--list} (@option{-t}) command to list an archive
3672 prints just the file names (one per line) and the other commands are
3673 silent. When used with most operations, the @option{--verbose}
3674 (@option{-v}) option causes @command{tar} to print the name of each
3675 file or archive member as it is processed. This and the other options
3676 which make @command{tar} print status information can be useful in
3677 monitoring @command{tar}.
3679 With @option{--create} or @option{--extract}, @option{--verbose} used
3680 once just prints the names of the files or members as they are processed.
3681 Using it twice causes @command{tar} to print a longer listing
3682 (@xref{verbose member listing}, for the description) for each member.
3683 Since @option{--list} already prints the names of the members,
3684 @option{--verbose} used once with @option{--list} causes @command{tar}
3685 to print an @samp{ls -l} type listing of the files in the archive.
3686 The following examples both extract members with long list output:
3689 $ @kbd{tar --extract --file=archive.tar --verbose --verbose}
3690 $ @kbd{tar xvvf archive.tar}
3693 Verbose output appears on the standard output except when an archive is
3694 being written to the standard output, as with @samp{tar --create
3695 --file=- --verbose} (@samp{tar cfv -}, or even @samp{tar cv}---if the
3696 installer let standard output be the default archive). In that case
3697 @command{tar} writes verbose output to the standard error stream.
3699 If @option{--index-file=@var{file}} is specified, @command{tar} sends
3700 verbose output to @var{file} rather than to standard output or standard
3704 @cindex Obtaining total status information
3706 The @option{--totals} option causes @command{tar} to print on the
3707 standard error the total amount of bytes transferred when processing
3708 an archive. When creating or appending to an archive, this option
3709 prints the number of bytes written to the archive and the average
3710 speed at which they have been written, e.g.:
3714 $ @kbd{tar -c -f archive.tar --totals /home}
3715 Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
3719 When reading an archive, this option displays the number of bytes
3724 $ @kbd{tar -x -f archive.tar --totals}
3725 Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
3729 Finally, when deleting from an archive, the @option{--totals} option
3730 displays both numbers plus number of bytes removed from the archive:
3734 $ @kbd{tar --delete -f foo.tar --totals --wildcards '*~'}
3735 Total bytes read: 9543680 (9.2MiB, 201MiB/s)
3736 Total bytes written: 3829760 (3.7MiB, 81MiB/s)
3737 Total bytes deleted: 1474048
3741 You can also obtain this information on request. When
3742 @option{--totals} is used with an argument, this argument is
3743 interpreted as a symbolic name of a signal, upon delivery of which the
3744 statistics is to be printed:
3747 @item --totals=@var{signo}
3748 Print statistics upon delivery of signal @var{signo}. Valid arguments
3749 are: @code{SIGHUP}, @code{SIGQUIT}, @code{SIGINT}, @code{SIGUSR1} and
3750 @code{SIGUSR2}. Shortened names without @samp{SIG} prefix are also
3754 Both forms of @option{--totals} option can be used simultaneously.
3755 Thus, @kbd{tar -x --totals --totals=USR1} instructs @command{tar} to
3756 extract all members from its default archive and print statistics
3757 after finishing the extraction, as well as when receiving signal
3760 @anchor{Progress information}
3761 @cindex Progress information
3762 The @option{--checkpoint} option prints an occasional message
3763 as @command{tar} reads or writes the archive. It is designed for
3764 those who don't need the more detailed (and voluminous) output of
3765 @option{--block-number} (@option{-R}), but do want visual confirmation
3766 that @command{tar} is actually making forward progress. By default it
3767 prints a message each 10 records read or written. This can be changed
3768 by giving it a numeric argument after an equal sign:
3771 $ @kbd{tar -c --checkpoint=1000} /var
3772 tar: Write checkpoint 1000
3773 tar: Write checkpoint 2000
3774 tar: Write checkpoint 3000
3777 This example shows the default checkpoint message used by
3778 @command{tar}. If you place a dot immediately after the equal
3779 sign, it will print a @samp{.} at each checkpoint@footnote{This is
3780 actually a shortcut for @option{--checkpoint=@var{n}
3781 --checkpoint-action=dot}. @xref{checkpoints, dot}.}. For example:
3784 $ @kbd{tar -c --checkpoint=.1000} /var
3788 The @option{--checkpoint} option provides a flexible mechanism for
3789 executing arbitrary actions upon hitting checkpoints, see the next
3790 section (@pxref{checkpoints}), for more information on it.
3792 @opindex show-omitted-dirs
3793 @anchor{show-omitted-dirs}
3794 The @option{--show-omitted-dirs} option, when reading an archive---with
3795 @option{--list} or @option{--extract}, for example---causes a message
3796 to be printed for each directory in the archive which is skipped.
3797 This happens regardless of the reason for skipping: the directory might
3798 not have been named on the command line (implicitly or explicitly),
3799 it might be excluded by the use of the
3800 @option{--exclude=@var{pattern}} option, or some other reason.
3802 @opindex block-number
3803 @cindex Block number where error occurred
3804 @anchor{block-number}
3805 If @option{--block-number} (@option{-R}) is used, @command{tar} prints, along with
3806 every message it would normally produce, the block number within the
3807 archive where the message was triggered. Also, supplementary messages
3808 are triggered when reading blocks full of NULs, or when hitting end of
3809 file on the archive. As of now, if the archive is properly terminated
3810 with a NUL block, the reading of the file may stop before end of file
3811 is met, so the position of end of file will not usually show when
3812 @option{--block-number} (@option{-R}) is used. Note that @GNUTAR{}
3813 drains the archive before exiting when reading the
3814 archive from a pipe.
3816 @cindex Error message, block number of
3817 This option is especially useful when reading damaged archives, since
3818 it helps pinpoint the damaged sections. It can also be used with
3819 @option{--list} (@option{-t}) when listing a file-system backup tape, allowing you to
3820 choose among several backup tapes when retrieving a file later, in
3821 favor of the tape where the file appears earliest (closest to the
3822 front of the tape). @xref{backup}.
3825 @section Checkpoints
3826 @cindex checkpoints, defined
3828 @opindex checkpoint-action
3830 A @dfn{checkpoint} is a moment of time before writing @var{n}th record to
3831 the archive (a @dfn{write checkpoint}), or before reading @var{n}th record
3832 from the archive (a @dfn{read checkpoint}). Checkpoints allow to
3833 periodically execute arbitrary actions.
3835 The checkpoint facility is enabled using the following option:
3838 @xopindex{checkpoint, defined}
3839 @item --checkpoint[=@var{n}]
3840 Schedule checkpoints before writing or reading each @var{n}th record.
3841 The default value for @var{n} is 10.
3844 A list of arbitrary @dfn{actions} can be executed at each checkpoint.
3845 These actions include: pausing, displaying textual messages, and
3846 executing arbitrary external programs. Actions are defined using
3847 the @option{--checkpoint-action} option.
3850 @xopindex{checkpoint-action, defined}
3851 @item --checkpoint-action=@var{action}
3852 Execute an @var{action} at each checkpoint.
3855 @cindex @code{echo}, checkpoint action
3856 The simplest value of @var{action} is @samp{echo}. It instructs
3857 @command{tar} to display the default message on the standard error
3858 stream upon arriving at each checkpoint. The default message is (in
3859 @acronym{POSIX} locale) @samp{Write checkpoint @var{n}}, for write
3860 checkpoints, and @samp{Read checkpoint @var{n}}, for read checkpoints.
3861 Here, @var{n} represents ordinal number of the checkpoint.
3863 In another locales, translated versions of this message are used.
3865 This is the default action, so running:
3868 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=echo} /var
3875 $ @kbd{tar -c --checkpoint=1000} /var
3878 The @samp{echo} action also allows to supply a customized message.
3879 You do so by placing an equals sign and the message right after it,
3883 --checkpoint-action="echo=Hit %s checkpoint #%u"
3886 The @samp{%s} and @samp{%u} in the above example are
3887 @dfn{meta-characters}. The @samp{%s} meta-character is replaced with
3888 the @dfn{type} of the checkpoint: @samp{write} or
3889 @samp{read} (or a corresponding translated version in locales other
3890 than @acronym{POSIX}). The @samp{%u} meta-character is replaced with
3891 the ordinal number of the checkpoint. Thus, the above example could
3892 produce the following output when used with the @option{--create}
3896 tar: Hit write checkpoint #10
3897 tar: Hit write checkpoint #20
3898 tar: Hit write checkpoint #30
3901 Aside from meta-character expansion, the message string is subject to
3902 @dfn{unquoting}, during which the backslash @dfn{escape sequences} are
3903 replaced with their corresponding @acronym{ASCII} characters
3904 (@pxref{escape sequences}). E.g. the following action will produce an
3905 audible bell and the message described above at each checkpoint:
3908 --checkpoint-action='echo=\aHit %s checkpoint #%u'
3911 @cindex @code{bell}, checkpoint action
3912 There is also a special action which produces an audible signal:
3913 @samp{bell}. It is not equivalent to @samp{echo='\a'}, because
3914 @samp{bell} sends the bell directly to the console (@file{/dev/tty}),
3915 whereas @samp{echo='\a'} sends it to the standard error.
3917 @cindex @code{ttyout}, checkpoint action
3918 The @samp{ttyout=@var{string}} action outputs @var{string} to
3919 @file{/dev/tty}, so it can be used even if the standard output is
3920 redirected elsewhere. The @var{string} is subject to the same
3921 modifications as with @samp{echo} action. In contrast to the latter,
3922 @samp{ttyout} does not prepend @command{tar} executable name to the
3923 string, nor does it output a newline after it. For example, the
3924 following action will print the checkpoint message at the same screen
3925 line, overwriting any previous message:
3928 --checkpoint-action="ttyout=\rHit %s checkpoint #%u"
3931 @cindex @code{dot}, checkpoint action
3932 Another available checkpoint action is @samp{dot} (or @samp{.}). It
3933 instructs @command{tar} to print a single dot on the standard listing
3937 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=dot} /var
3941 For compatibility with previous @GNUTAR{} versions, this action can
3942 be abbreviated by placing a dot in front of the checkpoint frequency,
3943 as shown in the previous section.
3945 @cindex @code{sleep}, checkpoint action
3946 Yet another action, @samp{sleep}, pauses @command{tar} for a specified
3947 amount of seconds. The following example will stop for 30 seconds at each
3951 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=sleep=30}
3954 @cindex @code{exec}, checkpoint action
3955 Finally, the @code{exec} action executes a given external program.
3959 $ @kbd{tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint}
3962 This program is executed using @command{/bin/sh -c}, with no
3963 additional arguments. Its exit code is ignored. It gets a copy of
3964 @command{tar}'s environment plus the following variables:
3967 @vrindex TAR_VERSION, checkpoint script environment
3969 @GNUTAR{} version number.
3971 @vrindex TAR_ARCHIVE, checkpoint script environment
3973 The name of the archive @command{tar} is processing.
3975 @vrindex TAR_BLOCKING_FACTOR, checkpoint script environment
3976 @item TAR_BLOCKING_FACTOR
3977 Current blocking factor (@pxref{Blocking}).
3979 @vrindex TAR_CHECKPOINT, checkpoint script environment
3980 @item TAR_CHECKPOINT
3981 Number of the checkpoint.
3983 @vrindex TAR_SUBCOMMAND, checkpoint script environment
3984 @item TAR_SUBCOMMAND
3985 A short option describing the operation @command{tar} is executing.
3986 @xref{Operations}, for a complete list of subcommand options.
3988 @vrindex TAR_FORMAT, checkpoint script environment
3990 Format of the archive being processed. @xref{Formats}, for a complete
3991 list of archive format names.
3994 Any number of actions can be defined, by supplying several
3995 @option{--checkpoint-action} options in the command line. For
3996 example, the command below displays two messages, pauses
3997 execution for 30 seconds and executes the @file{/sbin/cpoint} script:
4001 $ @kbd{tar -c -f arc.tar \
4002 --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
4003 --checkpoint-action='echo=Sleeping for 30 seconds' \
4004 --checkpoint-action='sleep=30' \
4005 --checkpoint-action='exec=/sbin/cpoint'}
4009 This example also illustrates the fact that
4010 @option{--checkpoint-action} can be used without
4011 @option{--checkpoint}. In this case, the default checkpoint frequency
4012 (at each 10th record) is assumed.
4015 @section Controlling Warning Messages
4017 Sometimes, while performing the requested task, @GNUTAR{} notices
4018 some conditions that are not exactly erros, but which the user
4019 should be aware of. When this happens, @command{tar} issues a
4020 @dfn{warning message} describing the condition. Warning messages
4021 are output to the standard error and they do not affect the exit
4022 code of @command{tar} command.
4024 @xopindex{warning, explained}
4025 @GNUTAR{} allows the user to suppress some or all of its warning
4029 @item --warning=@var{keyword}
4030 Control display of the warning messages identified by @var{keyword}.
4031 If @var{keyword} starts with the prefix @samp{no-}, such messages are
4032 suppressed. Otherwise, they are enabled.
4034 Multiple @option{--warning} messages accumulate.
4036 The tables below list allowed values for @var{keyword} along with the
4037 warning messages they control.
4040 @subheading Keywords controlling @command{tar} operation
4044 Enable all warning messages. This is the default.
4047 Disable all warning messages.
4048 @kwindex filename-with-nuls
4049 @cindex @samp{file name read contains nul character}, warning message
4050 @item filename-with-nuls
4051 @samp{%s: file name read contains nul character}
4052 @kwindex alone-zero-block
4053 @cindex @samp{A lone zero block at}, warning message
4054 @item alone-zero-block
4055 @samp{A lone zero block at %s}
4058 @subheading Keywords applicable for @command{tar --create}
4061 @cindex @samp{contains a cache directory tag}, warning message
4063 @samp{%s: contains a cache directory tag %s; %s}
4064 @kwindex file-shrank
4065 @cindex @samp{File shrank by %s bytes}, warning message
4067 @samp{%s: File shrank by %s bytes; padding with zeros}
4069 @cindex @samp{file is on a different filesystem}, warning message
4071 @samp{%s: file is on a different filesystem; not dumped}
4072 @kwindex file-ignored
4073 @cindex @samp{Unknown file type; file ignored}, warning message
4074 @cindex @samp{socket ignored}, warning message
4075 @cindex @samp{door ignored}, warning message
4077 @samp{%s: Unknown file type; file ignored}
4078 @samp{%s: socket ignored}
4079 @*@samp{%s: door ignored}
4080 @kwindex file-unchanged
4081 @cindex @samp{file is unchanged; not dumped}, warning message
4082 @item file-unchanged
4083 @samp{%s: file is unchanged; not dumped}
4084 @kwindex ignore-archive
4085 @cindex @samp{file is the archive; not dumped}, warning message
4086 @kwindex ignore-archive
4087 @cindex @samp{file is the archive; not dumped}, warning message
4088 @item ignore-archive
4089 @samp{%s: file is the archive; not dumped}
4090 @kwindex file-removed
4091 @cindex @samp{File removed before we read it}, warning message
4093 @samp{%s: File removed before we read it}
4094 @kwindex file-changed
4095 @cindex @samp{file changed as we read it}, warning message
4097 @samp{%s: file changed as we read it}
4100 @subheading Keywords applicable for @command{tar --extract}
4103 @cindex @samp{implausibly old time stamp %s}, warning message
4104 @cindex @samp{time stamp %s is %s s in the future}, warning message
4106 @samp{%s: implausibly old time stamp %s}
4107 @*@samp{%s: time stamp %s is %s s in the future}
4108 @kwindex contiguous-cast
4109 @cindex @samp{Extracting contiguous files as regular files}, warning message
4110 @item contiguous-cast
4111 @samp{Extracting contiguous files as regular files}
4112 @kwindex symlink-cast
4113 @cindex @samp{Attempting extraction of symbolic links as hard links}, warning message
4115 @samp{Attempting extraction of symbolic links as hard links}
4116 @kwindex unknown-cast
4117 @cindex @samp{Unknown file type `%c', extracted as normal file}, warning message
4119 @samp{%s: Unknown file type `%c', extracted as normal file}
4120 @kwindex ignore-newer
4121 @cindex @samp{Current %s is newer or same age}, warning message
4123 @samp{Current %s is newer or same age}
4124 @kwindex unknown-keyword
4125 @cindex @samp{Ignoring unknown extended header keyword `%s'}, warning message
4126 @item unknown-keyword
4127 @samp{Ignoring unknown extended header keyword `%s'}
4130 @subheading Keywords controlling incremental extraction:
4132 @kwindex rename-directory
4133 @cindex @samp{%s: Directory has been renamed from %s}, warning message
4134 @cindex @samp{%s: Directory has been renamed}, warning message
4135 @item rename-directory
4136 @samp{%s: Directory has been renamed from %s}
4137 @*@samp{%s: Directory has been renamed}
4138 @kwindex new-directory
4139 @cindex @samp{%s: Directory is new}, warning message
4141 @samp{%s: Directory is new}
4143 @cindex @samp{%s: directory is on a different device: not purging}, warning message
4145 @samp{%s: directory is on a different device: not purging}
4146 @kwindex bad-dumpdir
4147 @cindex @samp{Malformed dumpdir: 'X' never used}, warning message
4149 @samp{Malformed dumpdir: 'X' never used}
4153 @section Asking for Confirmation During Operations
4154 @cindex Interactive operation
4156 Typically, @command{tar} carries out a command without stopping for
4157 further instructions. In some situations however, you may want to
4158 exclude some files and archive members from the operation (for instance
4159 if disk or storage space is tight). You can do this by excluding
4160 certain files automatically (@pxref{Choosing}), or by performing
4161 an operation interactively, using the @option{--interactive} (@option{-w}) option.
4162 @command{tar} also accepts @option{--confirmation} for this option.
4164 @opindex interactive
4165 When the @option{--interactive} (@option{-w}) option is specified, before
4166 reading, writing, or deleting files, @command{tar} first prints a message
4167 for each such file, telling what operation it intends to take, then asks
4168 for confirmation on the terminal. The actions which require
4169 confirmation include adding a file to the archive, extracting a file
4170 from the archive, deleting a file from the archive, and deleting a file
4171 from disk. To confirm the action, you must type a line of input
4172 beginning with @samp{y}. If your input line begins with anything other
4173 than @samp{y}, @command{tar} skips that file.
4175 If @command{tar} is reading the archive from the standard input,
4176 @command{tar} opens the file @file{/dev/tty} to support the interactive
4179 Verbose output is normally sent to standard output, separate from
4180 other error messages. However, if the archive is produced directly
4181 on standard output, then verbose output is mixed with errors on
4182 @code{stderr}. Producing the archive on standard output may be used
4183 as a way to avoid using disk space, when the archive is soon to be
4184 consumed by another process reading it, say. Some people felt the need
4185 of producing an archive on stdout, still willing to segregate between
4186 verbose output and error output. A possible approach would be using a
4187 named pipe to receive the archive, and having the consumer process to
4188 read from that named pipe. This has the advantage of letting standard
4189 output free to receive verbose output, all separate from errors.
4192 @chapter @GNUTAR{} Operations
4205 @section Basic @GNUTAR{} Operations
4207 The basic @command{tar} operations, @option{--create} (@option{-c}),
4208 @option{--list} (@option{-t}) and @option{--extract} (@option{--get},
4209 @option{-x}), are currently presented and described in the tutorial
4210 chapter of this manual. This section provides some complementary notes
4211 for these operations.
4214 @xopindex{create, complementary notes}
4218 Creating an empty archive would have some kind of elegance. One can
4219 initialize an empty archive and later use @option{--append}
4220 (@option{-r}) for adding all members. Some applications would not
4221 welcome making an exception in the way of adding the first archive
4222 member. On the other hand, many people reported that it is
4223 dangerously too easy for @command{tar} to destroy a magnetic tape with
4224 an empty archive@footnote{This is well described in @cite{Unix-haters
4225 Handbook}, by Simson Garfinkel, Daniel Weise & Steven Strassmann, IDG
4226 Books, ISBN 1-56884-203-1.}. The two most common errors are:
4230 Mistakingly using @code{create} instead of @code{extract}, when the
4231 intent was to extract the full contents of an archive. This error
4232 is likely: keys @kbd{c} and @kbd{x} are right next to each other on
4233 the QWERTY keyboard. Instead of being unpacked, the archive then
4234 gets wholly destroyed. When users speak about @dfn{exploding} an
4235 archive, they usually mean something else :-).
4238 Forgetting the argument to @code{file}, when the intent was to create
4239 an archive with a single file in it. This error is likely because a
4240 tired user can easily add the @kbd{f} key to the cluster of option
4241 letters, by the mere force of habit, without realizing the full
4242 consequence of doing so. The usual consequence is that the single
4243 file, which was meant to be saved, is rather destroyed.
4246 So, recognizing the likelihood and the catastrophic nature of these
4247 errors, @GNUTAR{} now takes some distance from elegance, and
4248 cowardly refuses to create an archive when @option{--create} option is
4249 given, there are no arguments besides options, and
4250 @option{--files-from} (@option{-T}) option is @emph{not} used. To get
4251 around the cautiousness of @GNUTAR{} and nevertheless create an
4252 archive with nothing in it, one may still use, as the value for the
4253 @option{--files-from} option, a file with no names in it, as shown in
4254 the following commands:
4257 @kbd{tar --create --file=empty-archive.tar --files-from=/dev/null}
4258 @kbd{tar cfT empty-archive.tar /dev/null}
4261 @xopindex{extract, complementary notes}
4266 A socket is stored, within a @GNUTAR{} archive, as a pipe.
4268 @item @option{--list} (@option{-t})
4270 @GNUTAR{} now shows dates as @samp{1996-08-30},
4271 while it used to show them as @samp{Aug 30 1996}. Preferably,
4272 people should get used to ISO 8601 dates. Local American dates should
4273 be made available again with full date localization support, once
4274 ready. In the meantime, programs not being localizable for dates
4275 should prefer international dates, that's really the way to go.
4277 Look up @url{http://www.cl.cam.ac.uk/@/~mgk25/@/iso-time.html} if you
4278 are curious, it contains a detailed explanation of the ISO 8601 standard.
4283 @section Advanced @GNUTAR{} Operations
4285 Now that you have learned the basics of using @GNUTAR{}, you may want
4286 to learn about further ways in which @command{tar} can help you.
4288 This chapter presents five, more advanced operations which you probably
4289 won't use on a daily basis, but which serve more specialized functions.
4290 We also explain the different styles of options and why you might want
4291 to use one or another, or a combination of them in your @command{tar}
4292 commands. Additionally, this chapter includes options which allow you to
4293 define the output from @command{tar} more carefully, and provide help and
4294 error correction in special circumstances.
4296 @FIXME{check this after the chapter is actually revised to make sure
4297 it still introduces the info in the chapter correctly : ).}
4309 @subsection The Five Advanced @command{tar} Operations
4311 @cindex basic operations
4312 In the last chapter, you learned about the first three operations to
4313 @command{tar}. This chapter presents the remaining five operations to
4314 @command{tar}: @option{--append}, @option{--update}, @option{--concatenate},
4315 @option{--delete}, and @option{--compare}.
4317 You are not likely to use these operations as frequently as those
4318 covered in the last chapter; however, since they perform specialized
4319 functions, they are quite useful when you do need to use them. We
4320 will give examples using the same directory and files that you created
4321 in the last chapter. As you may recall, the directory is called
4322 @file{practice}, the files are @samp{jazz}, @samp{blues}, @samp{folk},
4323 @samp{rock}, and the two archive files you created are
4324 @samp{collection.tar} and @samp{music.tar}.
4326 We will also use the archive files @samp{afiles.tar} and
4327 @samp{bfiles.tar}. The archive @samp{afiles.tar} contains the members @samp{apple},
4328 @samp{angst}, and @samp{aspic}; @samp{bfiles.tar} contains the members
4329 @samp{./birds}, @samp{baboon}, and @samp{./box}.
4331 Unless we state otherwise, all practicing you do and examples you follow
4332 in this chapter will take place in the @file{practice} directory that
4333 you created in the previous chapter; see @ref{prepare for examples}.
4334 (Below in this section, we will remind you of the state of the examples
4335 where the last chapter left them.)
4337 The five operations that we will cover in this chapter are:
4342 Add new entries to an archive that already exists.
4345 Add more recent copies of archive members to the end of an archive, if
4350 Add one or more pre-existing archives to the end of another archive.
4352 Delete items from an archive (does not work on tapes).
4356 Compare archive members to their counterparts in the file system.
4360 @subsection How to Add Files to Existing Archives: @option{--append}
4362 @cindex appending files to existing archive
4364 If you want to add files to an existing archive, you don't need to
4365 create a new archive; you can use @option{--append} (@option{-r}).
4366 The archive must already exist in order to use @option{--append}. (A
4367 related operation is the @option{--update} operation; you can use this
4368 to add newer versions of archive members to an existing archive. To learn how to
4369 do this with @option{--update}, @pxref{update}.)
4371 If you use @option{--append} to add a file that has the same name as an
4372 archive member to an archive containing that archive member, then the
4373 old member is not deleted. What does happen, however, is somewhat
4374 complex. @command{tar} @emph{allows} you to have infinite number of files
4375 with the same name. Some operations treat these same-named members no
4376 differently than any other set of archive members: for example, if you
4377 view an archive with @option{--list} (@option{-t}), you will see all
4378 of those members listed, with their data modification times, owners, etc.
4380 Other operations don't deal with these members as perfectly as you might
4381 prefer; if you were to use @option{--extract} to extract the archive,
4382 only the most recently added copy of a member with the same name as four
4383 other members would end up in the working directory. This is because
4384 @option{--extract} extracts an archive in the order the members appeared
4385 in the archive; the most recently archived members will be extracted
4386 last. Additionally, an extracted member will @emph{replace} a file of
4387 the same name which existed in the directory already, and @command{tar}
4388 will not prompt you about this@footnote{Unless you give it
4389 @option{--keep-old-files} option, or the disk copy is newer than the
4390 the one in the archive and you invoke @command{tar} with
4391 @option{--keep-newer-files} option}. Thus, only the most recently archived
4392 member will end up being extracted, as it will replace the one
4393 extracted before it, and so on.
4395 @cindex extracting @var{n}th copy of the file
4396 @xopindex{occurrence, described}
4397 There exists a special option that allows you to get around this
4398 behavior and extract (or list) only a particular copy of the file.
4399 This is @option{--occurrence} option. If you run @command{tar} with
4400 this option, it will extract only the first copy of the file. You
4401 may also give this option an argument specifying the number of
4402 copy to be extracted. Thus, for example if the archive
4403 @file{archive.tar} contained three copies of file @file{myfile}, then
4407 tar --extract --file archive.tar --occurrence=2 myfile
4411 would extract only the second copy. @xref{Option
4412 Summary,---occurrence}, for the description of @option{--occurrence}
4415 @FIXME{ hag -- you might want to incorporate some of the above into the
4416 MMwtSN node; not sure. i didn't know how to make it simpler...
4418 There are a few ways to get around this. (maybe xref Multiple Members
4419 with the Same Name.}
4421 @cindex Members, replacing with other members
4422 @cindex Replacing members with other members
4423 @xopindex{delete, using before --append}
4424 If you want to replace an archive member, use @option{--delete} to
4425 delete the member you want to remove from the archive, and then use
4426 @option{--append} to add the member you want to be in the archive. Note
4427 that you can not change the order of the archive; the most recently
4428 added member will still appear last. In this sense, you cannot truly
4429 ``replace'' one member with another. (Replacing one member with another
4430 will not work on certain types of media, such as tapes; see @ref{delete}
4431 and @ref{Media}, for more information.)
4434 * appending files:: Appending Files to an Archive
4438 @node appending files
4439 @subsubsection Appending Files to an Archive
4440 @cindex Adding files to an Archive
4441 @cindex Appending files to an Archive
4442 @cindex Archives, Appending files to
4445 The simplest way to add a file to an already existing archive is the
4446 @option{--append} (@option{-r}) operation, which writes specified
4447 files into the archive whether or not they are already among the
4450 When you use @option{--append}, you @emph{must} specify file name
4451 arguments, as there is no default. If you specify a file that already
4452 exists in the archive, another copy of the file will be added to the
4453 end of the archive. As with other operations, the member names of the
4454 newly added files will be exactly the same as their names given on the
4455 command line. The @option{--verbose} (@option{-v}) option will print
4456 out the names of the files as they are written into the archive.
4458 @option{--append} cannot be performed on some tape drives, unfortunately,
4459 due to deficiencies in the formats those tape drives use. The archive
4460 must be a valid @command{tar} archive, or else the results of using this
4461 operation will be unpredictable. @xref{Media}.
4463 To demonstrate using @option{--append} to add a file to an archive,
4464 create a file called @file{rock} in the @file{practice} directory.
4465 Make sure you are in the @file{practice} directory. Then, run the
4466 following @command{tar} command to add @file{rock} to
4467 @file{collection.tar}:
4470 $ @kbd{tar --append --file=collection.tar rock}
4474 If you now use the @option{--list} (@option{-t}) operation, you will see that
4475 @file{rock} has been added to the archive:
4478 $ @kbd{tar --list --file=collection.tar}
4479 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4480 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4481 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4482 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4486 @subsubsection Multiple Members with the Same Name
4487 @cindex members, multiple
4488 @cindex multiple members
4490 You can use @option{--append} (@option{-r}) to add copies of files
4491 which have been updated since the archive was created. (However, we
4492 do not recommend doing this since there is another @command{tar}
4493 option called @option{--update}; @xref{update}, for more information.
4494 We describe this use of @option{--append} here for the sake of
4495 completeness.) When you extract the archive, the older version will
4496 be effectively lost. This works because files are extracted from an
4497 archive in the order in which they were archived. Thus, when the
4498 archive is extracted, a file archived later in time will replace a
4499 file of the same name which was archived earlier, even though the
4500 older version of the file will remain in the archive unless you delete
4501 all versions of the file.
4503 Supposing you change the file @file{blues} and then append the changed
4504 version to @file{collection.tar}. As you saw above, the original
4505 @file{blues} is in the archive @file{collection.tar}. If you change the
4506 file and append the new version of the file to the archive, there will
4507 be two copies in the archive. When you extract the archive, the older
4508 version of the file will be extracted first, and then replaced by the
4509 newer version when it is extracted.
4511 You can append the new, changed copy of the file @file{blues} to the
4512 archive in this way:
4515 $ @kbd{tar --append --verbose --file=collection.tar blues}
4520 Because you specified the @option{--verbose} option, @command{tar} has
4521 printed the name of the file being appended as it was acted on. Now
4522 list the contents of the archive:
4525 $ @kbd{tar --list --verbose --file=collection.tar}
4526 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
4527 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4528 -rw-r--r-- me user 20 1996-09-23 16:44 folk
4529 -rw-r--r-- me user 20 1996-09-23 16:44 rock
4530 -rw-r--r-- me user 58 1996-10-24 18:30 blues
4534 The newest version of @file{blues} is now at the end of the archive
4535 (note the different creation dates and file sizes). If you extract
4536 the archive, the older version of the file @file{blues} will be
4537 replaced by the newer version. You can confirm this by extracting
4538 the archive and running @samp{ls} on the directory.
4540 If you wish to extract the first occurrence of the file @file{blues}
4541 from the archive, use @option{--occurrence} option, as shown in
4542 the following example:
4545 $ @kbd{tar --extract -vv --occurrence --file=collection.tar blues}
4546 -rw-r--r-- me user 21 1996-09-23 16:44 blues
4549 @xref{Writing}, for more information on @option{--extract} and
4550 @xref{Option Summary, --occurrence}, for the description of
4551 @option{--occurrence} option.
4554 @subsection Updating an Archive
4555 @cindex Updating an archive
4558 In the previous section, you learned how to use @option{--append} to
4559 add a file to an existing archive. A related operation is
4560 @option{--update} (@option{-u}). The @option{--update} operation
4561 updates a @command{tar} archive by comparing the date of the specified
4562 archive members against the date of the file with the same name. If
4563 the file has been modified more recently than the archive member, then
4564 the newer version of the file is added to the archive (as with
4567 Unfortunately, you cannot use @option{--update} with magnetic tape drives.
4568 The operation will fail.
4570 @FIXME{other examples of media on which --update will fail? need to ask
4571 charles and/or mib/thomas/dave shevett..}
4573 Both @option{--update} and @option{--append} work by adding to the end
4574 of the archive. When you extract a file from the archive, only the
4575 version stored last will wind up in the file system, unless you use
4576 the @option{--backup} option. @xref{multiple}, for a detailed discussion.
4583 @subsubsection How to Update an Archive Using @option{--update}
4586 You must use file name arguments with the @option{--update}
4587 (@option{-u}) operation. If you don't specify any files,
4588 @command{tar} won't act on any files and won't tell you that it didn't
4589 do anything (which may end up confusing you).
4591 @c note: the above parenthetical added because in fact, this
4592 @c behavior just confused the author. :-)
4594 To see the @option{--update} option at work, create a new file,
4595 @file{classical}, in your practice directory, and some extra text to the
4596 file @file{blues}, using any text editor. Then invoke @command{tar} with
4597 the @samp{update} operation and the @option{--verbose} (@option{-v})
4598 option specified, using the names of all the files in the practice
4599 directory as file name arguments:
4602 $ @kbd{tar --update -v -f collection.tar blues folk rock classical}
4609 Because we have specified verbose mode, @command{tar} prints out the names
4610 of the files it is working on, which in this case are the names of the
4611 files that needed to be updated. If you run @samp{tar --list} and look
4612 at the archive, you will see @file{blues} and @file{classical} at its
4613 end. There will be a total of two versions of the member @samp{blues};
4614 the one at the end will be newer and larger, since you added text before
4617 (The reason @command{tar} does not overwrite the older file when updating
4618 it is because writing to the middle of a section of tape is a difficult
4619 process. Tapes are not designed to go backward. @xref{Media}, for more
4620 information about tapes.
4622 @option{--update} (@option{-u}) is not suitable for performing backups for two
4623 reasons: it does not change directory content entries, and it
4624 lengthens the archive every time it is used. The @GNUTAR{}
4625 options intended specifically for backups are more
4626 efficient. If you need to run backups, please consult @ref{Backups}.
4629 @subsection Combining Archives with @option{--concatenate}
4631 @cindex Adding archives to an archive
4632 @cindex Concatenating Archives
4633 @opindex concatenate
4635 @c @cindex @option{-A} described
4636 Sometimes it may be convenient to add a second archive onto the end of
4637 an archive rather than adding individual files to the archive. To add
4638 one or more archives to the end of another archive, you should use the
4639 @option{--concatenate} (@option{--catenate}, @option{-A}) operation.
4641 To use @option{--concatenate}, give the first archive with
4642 @option{--file} option and name the rest of archives to be
4643 concatenated on the command line. The members, and their member
4644 names, will be copied verbatim from those archives to the first one.
4645 @footnote{This can cause multiple members to have the same name, for
4646 information on how this affects reading the archive, @ref{multiple}.}
4647 The new, concatenated archive will be called by the same name as the
4648 one given with the @option{--file} option. As usual, if you omit
4649 @option{--file}, @command{tar} will use the value of the environment
4650 variable @env{TAPE}, or, if this has not been set, the default archive name.
4652 @FIXME{There is no way to specify a new name...}
4654 To demonstrate how @option{--concatenate} works, create two small archives
4655 called @file{bluesrock.tar} and @file{folkjazz.tar}, using the relevant
4656 files from @file{practice}:
4659 $ @kbd{tar -cvf bluesrock.tar blues rock}
4662 $ @kbd{tar -cvf folkjazz.tar folk jazz}
4668 If you like, You can run @samp{tar --list} to make sure the archives
4669 contain what they are supposed to:
4672 $ @kbd{tar -tvf bluesrock.tar}
4673 -rw-r--r-- melissa user 105 1997-01-21 19:42 blues
4674 -rw-r--r-- melissa user 33 1997-01-20 15:34 rock
4675 $ @kbd{tar -tvf jazzfolk.tar}
4676 -rw-r--r-- melissa user 20 1996-09-23 16:44 folk
4677 -rw-r--r-- melissa user 65 1997-01-30 14:15 jazz
4680 We can concatenate these two archives with @command{tar}:
4684 $ @kbd{tar --concatenate --file=bluesrock.tar jazzfolk.tar}
4687 If you now list the contents of the @file{bluesrock.tar}, you will see
4688 that now it also contains the archive members of @file{jazzfolk.tar}:
4691 $ @kbd{tar --list --file=bluesrock.tar}
4698 When you use @option{--concatenate}, the source and target archives must
4699 already exist and must have been created using compatible format
4700 parameters. Notice, that @command{tar} does not check whether the
4701 archives it concatenates have compatible formats, it does not
4702 even check if the files are really tar archives.
4704 Like @option{--append} (@option{-r}), this operation cannot be performed on some
4705 tape drives, due to deficiencies in the formats those tape drives use.
4707 @cindex @code{concatenate} vs @command{cat}
4708 @cindex @command{cat} vs @code{concatenate}
4709 It may seem more intuitive to you to want or try to use @command{cat} to
4710 concatenate two archives instead of using the @option{--concatenate}
4711 operation; after all, @command{cat} is the utility for combining files.
4713 However, @command{tar} archives incorporate an end-of-file marker which
4714 must be removed if the concatenated archives are to be read properly as
4715 one archive. @option{--concatenate} removes the end-of-archive marker
4716 from the target archive before each new archive is appended. If you use
4717 @command{cat} to combine the archives, the result will not be a valid
4718 @command{tar} format archive. If you need to retrieve files from an
4719 archive that was added to using the @command{cat} utility, use the
4720 @option{--ignore-zeros} (@option{-i}) option. @xref{Ignore Zeros}, for further
4721 information on dealing with archives improperly combined using the
4722 @command{cat} shell utility.
4725 @subsection Removing Archive Members Using @option{--delete}
4726 @cindex Deleting files from an archive
4727 @cindex Removing files from an archive
4730 You can remove members from an archive by using the @option{--delete}
4731 option. Specify the name of the archive with @option{--file}
4732 (@option{-f}) and then specify the names of the members to be deleted;
4733 if you list no member names, nothing will be deleted. The
4734 @option{--verbose} option will cause @command{tar} to print the names
4735 of the members as they are deleted. As with @option{--extract}, you
4736 must give the exact member names when using @samp{tar --delete}.
4737 @option{--delete} will remove all versions of the named file from the
4738 archive. The @option{--delete} operation can run very slowly.
4740 Unlike other operations, @option{--delete} has no short form.
4742 @cindex Tapes, using @option{--delete} and
4743 @cindex Deleting from tape archives
4744 This operation will rewrite the archive. You can only use
4745 @option{--delete} on an archive if the archive device allows you to
4746 write to any point on the media, such as a disk; because of this, it
4747 does not work on magnetic tapes. Do not try to delete an archive member
4748 from a magnetic tape; the action will not succeed, and you will be
4749 likely to scramble the archive and damage your tape. There is no safe
4750 way (except by completely re-writing the archive) to delete files from
4751 most kinds of magnetic tape. @xref{Media}.
4753 To delete all versions of the file @file{blues} from the archive
4754 @file{collection.tar} in the @file{practice} directory, make sure you
4755 are in that directory, and then,
4758 $ @kbd{tar --list --file=collection.tar}
4763 $ @kbd{tar --delete --file=collection.tar blues}
4764 $ @kbd{tar --list --file=collection.tar}
4771 @FIXME{Check if the above listing is actually produced after running
4772 all the examples on collection.tar.}
4774 The @option{--delete} option has been reported to work properly when
4775 @command{tar} acts as a filter from @code{stdin} to @code{stdout}.
4778 @subsection Comparing Archive Members with the File System
4779 @cindex Verifying the currency of an archive
4782 The @option{--compare} (@option{-d}), or @option{--diff} operation compares
4783 specified archive members against files with the same names, and then
4784 reports differences in file size, mode, owner, modification date and
4785 contents. You should @emph{only} specify archive member names, not file
4786 names. If you do not name any members, then @command{tar} will compare the
4787 entire archive. If a file is represented in the archive but does not
4788 exist in the file system, @command{tar} reports a difference.
4790 You have to specify the record size of the archive when modifying an
4791 archive with a non-default record size.
4793 @command{tar} ignores files in the file system that do not have
4794 corresponding members in the archive.
4796 The following example compares the archive members @file{rock},
4797 @file{blues} and @file{funk} in the archive @file{bluesrock.tar} with
4798 files of the same name in the file system. (Note that there is no file,
4799 @file{funk}; @command{tar} will report an error message.)
4802 $ @kbd{tar --compare --file=bluesrock.tar rock blues funk}
4805 tar: funk not found in archive
4808 The spirit behind the @option{--compare} (@option{--diff},
4809 @option{-d}) option is to check whether the archive represents the
4810 current state of files on disk, more than validating the integrity of
4811 the archive media. For this later goal, @xref{verify}.
4813 @node create options
4814 @section Options Used by @option{--create}
4816 @xopindex{create, additional options}
4817 The previous chapter described the basics of how to use
4818 @option{--create} (@option{-c}) to create an archive from a set of files.
4819 @xref{create}. This section described advanced options to be used with
4823 * override:: Overriding File Metadata.
4824 * Ignore Failed Read::
4828 @subsection Overriding File Metadata
4830 As described above, a @command{tar} archive keeps, for each member it contains,
4831 its @dfn{metadata}, such as modification time, mode and ownership of
4832 the file. @GNUTAR{} allows to replace these data with other values
4833 when adding files to the archive. The options described in this
4834 section affect creation of archives of any type. For POSIX archives,
4835 see also @ref{PAX keywords}, for additional ways of controlling
4836 metadata, stored in the archive.
4840 @item --mode=@var{permissions}
4842 When adding files to an archive, @command{tar} will use
4843 @var{permissions} for the archive members, rather than the permissions
4844 from the files. @var{permissions} can be specified either as an octal
4845 number or as symbolic permissions, like with
4846 @command{chmod} (@xref{File permissions, Permissions, File
4847 permissions, fileutils, @acronym{GNU} file utilities}. This reference
4848 also has useful information for those not being overly familiar with
4849 the UNIX permission system). Using latter syntax allows for
4850 more flexibility. For example, the value @samp{a+rw} adds read and write
4851 permissions for everybody, while retaining executable bits on directories
4852 or on any other file already marked as executable:
4855 $ @kbd{tar -c -f archive.tar --mode='a+rw' .}
4858 @item --mtime=@var{date}
4861 When adding files to an archive, @command{tar} will use @var{date} as
4862 the modification time of members when creating archives, instead of
4863 their actual modification times. The argument @var{date} can be
4864 either a textual date representation in almost arbitrary format
4865 (@pxref{Date input formats}) or a name of the existing file, starting
4866 with @samp{/} or @samp{.}. In the latter case, the modification time
4867 of that file will be used.
4869 The following example will set the modification date to 00:00:00 UTC,
4873 $ @kbd{tar -c -f archive.tar --mtime='1970-01-01' .}
4877 When used with @option{--verbose} (@pxref{verbose tutorial}) @GNUTAR{}
4878 will try to convert the specified date back to its textual
4879 representation and compare it with the one given with
4880 @option{--mtime} options. If the two dates differ, @command{tar} will
4881 print a warning saying what date it will use. This is to help user
4882 ensure he is using the right date.
4887 $ @kbd{tar -c -f archive.tar -v --mtime=yesterday .}
4888 tar: Option --mtime: Treating date `yesterday' as 2006-06-20
4893 @item --owner=@var{user}
4896 Specifies that @command{tar} should use @var{user} as the owner of members
4897 when creating archives, instead of the user associated with the source
4898 file. The argument @var{user} can be either an existing user symbolic
4899 name, or a decimal numeric user @acronym{ID}.
4901 There is no value indicating a missing number, and @samp{0} usually means
4902 @code{root}. Some people like to force @samp{0} as the value to offer in
4903 their distributions for the owner of files, because the @code{root} user is
4904 anonymous anyway, so that might as well be the owner of anonymous
4905 archives. For example:
4909 $ @kbd{tar -c -f archive.tar --owner=0 .}
4911 $ @kbd{tar -c -f archive.tar --owner=root .}
4915 @item --group=@var{group}
4918 Files added to the @command{tar} archive will have a group @acronym{ID} of @var{group},
4919 rather than the group from the source file. The argument @var{group}
4920 can be either an existing group symbolic name, or a decimal numeric group @acronym{ID}.
4923 @node Ignore Failed Read
4924 @subsection Ignore Fail Read
4927 @item --ignore-failed-read
4928 @opindex ignore-failed-read
4929 Do not exit with nonzero on unreadable files or directories.
4932 @node extract options
4933 @section Options Used by @option{--extract}
4934 @cindex options for use with @option{--extract}
4936 @xopindex{extract, additional options}
4937 The previous chapter showed how to use @option{--extract} to extract
4938 an archive into the file system. Various options cause @command{tar} to
4939 extract more information than just file contents, such as the owner,
4940 the permissions, the modification date, and so forth. This section
4941 presents options to be used with @option{--extract} when certain special
4942 considerations arise. You may review the information presented in
4943 @ref{extract} for more basic information about the
4944 @option{--extract} operation.
4947 * Reading:: Options to Help Read Archives
4948 * Writing:: Changing How @command{tar} Writes Files
4949 * Scarce:: Coping with Scarce Resources
4953 @subsection Options to Help Read Archives
4954 @cindex Options when reading archives
4956 @cindex Reading incomplete records
4957 @cindex Records, incomplete
4958 @opindex read-full-records
4959 Normally, @command{tar} will request data in full record increments from
4960 an archive storage device. If the device cannot return a full record,
4961 @command{tar} will report an error. However, some devices do not always
4962 return full records, or do not require the last record of an archive to
4963 be padded out to the next record boundary. To keep reading until you
4964 obtain a full record, or to accept an incomplete record if it contains
4965 an end-of-archive marker, specify the @option{--read-full-records} (@option{-B}) option
4966 in conjunction with the @option{--extract} or @option{--list} operations.
4969 The @option{--read-full-records} (@option{-B}) option is turned on by default when
4970 @command{tar} reads an archive from standard input, or from a remote
4971 machine. This is because on @acronym{BSD} Unix systems, attempting to read a
4972 pipe returns however much happens to be in the pipe, even if it is
4973 less than was requested. If this option were not enabled, @command{tar}
4974 would fail as soon as it read an incomplete record from the pipe.
4976 If you're not sure of the blocking factor of an archive, you can
4977 read the archive by specifying @option{--read-full-records} (@option{-B}) and
4978 @option{--blocking-factor=@var{512-size}} (@option{-b
4979 @var{512-size}}), using a blocking factor larger than what the archive
4980 uses. This lets you avoid having to determine the blocking factor
4981 of an archive. @xref{Blocking Factor}.
4984 * read full records::
4988 @node read full records
4989 @unnumberedsubsubsec Reading Full Records
4991 @FIXME{need sentence or so of intro here}
4994 @opindex read-full-records
4995 @item --read-full-records
4997 Use in conjunction with @option{--extract} (@option{--get},
4998 @option{-x}) to read an archive which contains incomplete records, or
4999 one which has a blocking factor less than the one specified.
5003 @unnumberedsubsubsec Ignoring Blocks of Zeros
5005 @cindex End-of-archive blocks, ignoring
5006 @cindex Ignoring end-of-archive blocks
5007 @opindex ignore-zeros
5008 Normally, @command{tar} stops reading when it encounters a block of zeros
5009 between file entries (which usually indicates the end of the archive).
5010 @option{--ignore-zeros} (@option{-i}) allows @command{tar} to
5011 completely read an archive which contains a block of zeros before the
5012 end (i.e., a damaged archive, or one that was created by concatenating
5013 several archives together).
5015 The @option{--ignore-zeros} (@option{-i}) option is turned off by default because many
5016 versions of @command{tar} write garbage after the end-of-archive entry,
5017 since that part of the media is never supposed to be read. @GNUTAR{}
5018 does not write after the end of an archive, but seeks to
5019 maintain compatibility among archiving utilities.
5022 @item --ignore-zeros
5024 To ignore blocks of zeros (i.e., end-of-archive entries) which may be
5025 encountered while reading an archive. Use in conjunction with
5026 @option{--extract} or @option{--list}.
5030 @subsection Changing How @command{tar} Writes Files
5033 @FIXME{Introductory paragraph}
5036 * Dealing with Old Files::
5037 * Overwrite Old Files::
5039 * Keep Newer Files::
5041 * Recursive Unlink::
5042 * Data Modification Times::
5043 * Setting Access Permissions::
5044 * Directory Modification Times and Permissions::
5045 * Writing to Standard Output::
5046 * Writing to an External Program::
5050 @node Dealing with Old Files
5051 @unnumberedsubsubsec Options Controlling the Overwriting of Existing Files
5053 @xopindex{overwrite-dir, introduced}
5054 When extracting files, if @command{tar} discovers that the extracted
5055 file already exists, it normally replaces the file by removing it before
5056 extracting it, to prevent confusion in the presence of hard or symbolic
5057 links. (If the existing file is a symbolic link, it is removed, not
5058 followed.) However, if a directory cannot be removed because it is
5059 nonempty, @command{tar} normally overwrites its metadata (ownership,
5060 permission, etc.). The @option{--overwrite-dir} option enables this
5061 default behavior. To be more cautious and preserve the metadata of
5062 such a directory, use the @option{--no-overwrite-dir} option.
5064 @cindex Overwriting old files, prevention
5065 @xopindex{keep-old-files, introduced}
5066 To be even more cautious and prevent existing files from being replaced, use
5067 the @option{--keep-old-files} (@option{-k}) option. It causes @command{tar} to refuse
5068 to replace or update a file that already exists, i.e., a file with the
5069 same name as an archive member prevents extraction of that archive
5070 member. Instead, it reports an error.
5072 @xopindex{overwrite, introduced}
5073 To be more aggressive about altering existing files, use the
5074 @option{--overwrite} option. It causes @command{tar} to overwrite
5075 existing files and to follow existing symbolic links when extracting.
5077 @cindex Protecting old files
5078 Some people argue that @GNUTAR{} should not hesitate
5079 to overwrite files with other files when extracting. When extracting
5080 a @command{tar} archive, they expect to see a faithful copy of the
5081 state of the file system when the archive was created. It is debatable
5082 that this would always be a proper behavior. For example, suppose one
5083 has an archive in which @file{usr/local} is a link to
5084 @file{usr/local2}. Since then, maybe the site removed the link and
5085 renamed the whole hierarchy from @file{/usr/local2} to
5086 @file{/usr/local}. Such things happen all the time. I guess it would
5087 not be welcome at all that @GNUTAR{} removes the
5088 whole hierarchy just to make room for the link to be reinstated
5089 (unless it @emph{also} simultaneously restores the full
5090 @file{/usr/local2}, of course!) @GNUTAR{} is indeed
5091 able to remove a whole hierarchy to reestablish a symbolic link, for
5092 example, but @emph{only if} @option{--recursive-unlink} is specified
5093 to allow this behavior. In any case, single files are silently
5096 @xopindex{unlink-first, introduced}
5097 Finally, the @option{--unlink-first} (@option{-U}) option can improve performance in
5098 some cases by causing @command{tar} to remove files unconditionally
5099 before extracting them.
5101 @node Overwrite Old Files
5102 @unnumberedsubsubsec Overwrite Old Files
5107 Overwrite existing files and directory metadata when extracting files
5110 This causes @command{tar} to write extracted files into the file system without
5111 regard to the files already on the system; i.e., files with the same
5112 names as archive members are overwritten when the archive is extracted.
5113 It also causes @command{tar} to extract the ownership, permissions,
5114 and time stamps onto any preexisting files or directories.
5115 If the name of a corresponding file name is a symbolic link, the file
5116 pointed to by the symbolic link will be overwritten instead of the
5117 symbolic link itself (if this is possible). Moreover, special devices,
5118 empty directories and even symbolic links are automatically removed if
5119 they are in the way of extraction.
5121 Be careful when using the @option{--overwrite} option, particularly when
5122 combined with the @option{--absolute-names} (@option{-P}) option, as this combination
5123 can change the contents, ownership or permissions of any file on your
5124 system. Also, many systems do not take kindly to overwriting files that
5125 are currently being executed.
5127 @opindex overwrite-dir
5128 @item --overwrite-dir
5129 Overwrite the metadata of directories when extracting files from an
5130 archive, but remove other files before extracting.
5133 @node Keep Old Files
5134 @unnumberedsubsubsec Keep Old Files
5137 @opindex keep-old-files
5138 @item --keep-old-files
5140 Do not replace existing files from archive. The
5141 @option{--keep-old-files} (@option{-k}) option prevents @command{tar}
5142 from replacing existing files with files with the same name from the
5143 archive. The @option{--keep-old-files} option is meaningless with
5144 @option{--list} (@option{-t}). Prevents @command{tar} from replacing
5145 files in the file system during extraction.
5148 @node Keep Newer Files
5149 @unnumberedsubsubsec Keep Newer Files
5152 @opindex keep-newer-files
5153 @item --keep-newer-files
5154 Do not replace existing files that are newer than their archive
5155 copies. This option is meaningless with @option{--list} (@option{-t}).
5159 @unnumberedsubsubsec Unlink First
5162 @opindex unlink-first
5163 @item --unlink-first
5165 Remove files before extracting over them.
5166 This can make @command{tar} run a bit faster if you know in advance
5167 that the extracted files all need to be removed. Normally this option
5168 slows @command{tar} down slightly, so it is disabled by default.
5171 @node Recursive Unlink
5172 @unnumberedsubsubsec Recursive Unlink
5175 @opindex recursive-unlink
5176 @item --recursive-unlink
5177 When this option is specified, try removing files and directory hierarchies
5178 before extracting over them. @emph{This is a dangerous option!}
5181 If you specify the @option{--recursive-unlink} option,
5182 @command{tar} removes @emph{anything} that keeps you from extracting a file
5183 as far as current permissions will allow it. This could include removal
5184 of the contents of a full directory hierarchy.
5186 @node Data Modification Times
5187 @unnumberedsubsubsec Setting Data Modification Times
5189 @cindex Data modification times of extracted files
5190 @cindex Modification times of extracted files
5191 Normally, @command{tar} sets the data modification times of extracted
5192 files to the corresponding times recorded for the files in the archive, but
5193 limits the permissions of extracted files by the current @code{umask}
5196 To set the data modification times of extracted files to the time when
5197 the files were extracted, use the @option{--touch} (@option{-m}) option in
5198 conjunction with @option{--extract} (@option{--get}, @option{-x}).
5204 Sets the data modification time of extracted archive members to the time
5205 they were extracted, not the time recorded for them in the archive.
5206 Use in conjunction with @option{--extract} (@option{--get}, @option{-x}).
5209 @node Setting Access Permissions
5210 @unnumberedsubsubsec Setting Access Permissions
5212 @cindex Permissions of extracted files
5213 @cindex Modes of extracted files
5214 To set the modes (access permissions) of extracted files to those
5215 recorded for those files in the archive, use @option{--same-permissions}
5216 in conjunction with the @option{--extract} (@option{--get},
5217 @option{-x}) operation.
5220 @opindex preserve-permissions
5221 @opindex same-permissions
5222 @item --preserve-permissions
5223 @itemx --same-permissions
5224 @c @itemx --ignore-umask
5226 Set modes of extracted archive members to those recorded in the
5227 archive, instead of current umask settings. Use in conjunction with
5228 @option{--extract} (@option{--get}, @option{-x}).
5231 @node Directory Modification Times and Permissions
5232 @unnumberedsubsubsec Directory Modification Times and Permissions
5234 After successfully extracting a file member, @GNUTAR{} normally
5235 restores its permissions and modification times, as described in the
5236 previous sections. This cannot be done for directories, because
5237 after extracting a directory @command{tar} will almost certainly
5238 extract files into that directory and this will cause the directory
5239 modification time to be updated. Moreover, restoring that directory
5240 permissions may not permit file creation within it. Thus, restoring
5241 directory permissions and modification times must be delayed at least
5242 until all files have been extracted into that directory. @GNUTAR{}
5243 restores directories using the following approach.
5245 The extracted directories are created with the mode specified in the
5246 archive, as modified by the umask of the user, which gives sufficient
5247 permissions to allow file creation. The meta-information about the
5248 directory is recorded in the temporary list of directories. When
5249 preparing to extract next archive member, @GNUTAR{} checks if the
5250 directory prefix of this file contains the remembered directory. If
5251 it does not, the program assumes that all files have been extracted
5252 into that directory, restores its modification time and permissions
5253 and removes its entry from the internal list. This approach allows
5254 to correctly restore directory meta-information in the majority of
5255 cases, while keeping memory requirements sufficiently small. It is
5256 based on the fact, that most @command{tar} archives use the predefined
5257 order of members: first the directory, then all the files and
5258 subdirectories in that directory.
5260 However, this is not always true. The most important exception are
5261 incremental archives (@pxref{Incremental Dumps}). The member order in
5262 an incremental archive is reversed: first all directory members are
5263 stored, followed by other (non-directory) members. So, when extracting
5264 from incremental archives, @GNUTAR{} alters the above procedure. It
5265 remembers all restored directories, and restores their meta-data
5266 only after the entire archive has been processed. Notice, that you do
5267 not need to specify any special options for that, as @GNUTAR{}
5268 automatically detects archives in incremental format.
5270 There may be cases, when such processing is required for normal archives
5271 too. Consider the following example:
5275 $ @kbd{tar --no-recursion -cvf archive \
5276 foo foo/file1 bar bar/file foo/file2}
5285 During the normal operation, after encountering @file{bar}
5286 @GNUTAR{} will assume that all files from the directory @file{foo}
5287 were already extracted and will therefore restore its timestamp and
5288 permission bits. However, after extracting @file{foo/file2} the
5289 directory timestamp will be offset again.
5291 To correctly restore directory meta-information in such cases, use
5292 @option{delay-directory-restore} command line option:
5295 @opindex delay-directory-restore
5296 @item --delay-directory-restore
5297 Delays restoring of the modification times and permissions of extracted
5298 directories until the end of extraction. This way, correct
5299 meta-information is restored even if the archive has unusual member
5302 @opindex no-delay-directory-restore
5303 @item --no-delay-directory-restore
5304 Cancel the effect of the previous @option{--delay-directory-restore}.
5305 Use this option if you have used @option{--delay-directory-restore} in
5306 @env{TAR_OPTIONS} variable (@pxref{TAR_OPTIONS}) and wish to
5307 temporarily disable it.
5310 @node Writing to Standard Output
5311 @unnumberedsubsubsec Writing to Standard Output
5313 @cindex Writing extracted files to standard output
5314 @cindex Standard output, writing extracted files to
5315 To write the extracted files to the standard output, instead of
5316 creating the files on the file system, use @option{--to-stdout} (@option{-O}) in
5317 conjunction with @option{--extract} (@option{--get}, @option{-x}). This option is useful if you are
5318 extracting files to send them through a pipe, and do not need to
5319 preserve them in the file system. If you extract multiple members,
5320 they appear on standard output concatenated, in the order they are
5321 found in the archive.
5327 Writes files to the standard output. Use only in conjunction with
5328 @option{--extract} (@option{--get}, @option{-x}). When this option is
5329 used, instead of creating the files specified, @command{tar} writes
5330 the contents of the files extracted to its standard output. This may
5331 be useful if you are only extracting the files in order to send them
5332 through a pipe. This option is meaningless with @option{--list}
5336 This can be useful, for example, if you have a tar archive containing
5337 a big file and don't want to store the file on disk before processing
5338 it. You can use a command like this:
5341 tar -xOzf foo.tgz bigfile | process
5344 or even like this if you want to process the concatenation of the files:
5347 tar -xOzf foo.tgz bigfile1 bigfile2 | process
5350 However, @option{--to-command} may be more convenient for use with
5351 multiple files. See the next section.
5353 @node Writing to an External Program
5354 @unnumberedsubsubsec Writing to an External Program
5356 You can instruct @command{tar} to send the contents of each extracted
5357 file to the standard input of an external program:
5361 @item --to-command=@var{command}
5362 Extract files and pipe their contents to the standard input of
5363 @var{command}. When this option is used, instead of creating the
5364 files specified, @command{tar} invokes @var{command} and pipes the
5365 contents of the files to its standard output. @var{Command} may
5366 contain command line arguments. The program is executed via
5367 @code{sh -c}. Notice, that @var{command} is executed once for each regular file
5368 extracted. Non-regular files (directories, etc.) are ignored when this
5372 The command can obtain the information about the file it processes
5373 from the following environment variables:
5376 @vrindex TAR_FILETYPE, to-command environment
5378 Type of the file. It is a single letter with the following meaning:
5380 @multitable @columnfractions 0.10 0.90
5381 @item f @tab Regular file
5382 @item d @tab Directory
5383 @item l @tab Symbolic link
5384 @item h @tab Hard link
5385 @item b @tab Block device
5386 @item c @tab Character device
5389 Currently only regular files are supported.
5391 @vrindex TAR_MODE, to-command environment
5393 File mode, an octal number.
5395 @vrindex TAR_FILENAME, to-command environment
5397 The name of the file.
5399 @vrindex TAR_REALNAME, to-command environment
5401 Name of the file as stored in the archive.
5403 @vrindex TAR_UNAME, to-command environment
5405 Name of the file owner.
5407 @vrindex TAR_GNAME, to-command environment
5409 Name of the file owner group.
5411 @vrindex TAR_ATIME, to-command environment
5413 Time of last access. It is a decimal number, representing seconds
5414 since the Epoch. If the archive provides times with nanosecond
5415 precision, the nanoseconds are appended to the timestamp after a
5418 @vrindex TAR_MTIME, to-command environment
5420 Time of last modification.
5422 @vrindex TAR_CTIME, to-command environment
5424 Time of last status change.
5426 @vrindex TAR_SIZE, to-command environment
5430 @vrindex TAR_UID, to-command environment
5432 UID of the file owner.
5434 @vrindex TAR_GID, to-command environment
5436 GID of the file owner.
5439 Additionally, the following variables contain information about
5440 tar mode and the archive being processed:
5443 @vrindex TAR_VERSION, to-command environment
5445 @GNUTAR{} version number.
5447 @vrindex TAR_ARCHIVE, to-command environment
5449 The name of the archive @command{tar} is processing.
5451 @vrindex TAR_BLOCKING_FACTOR, to-command environment
5452 @item TAR_BLOCKING_FACTOR
5453 Current blocking factor (@pxref{Blocking}.
5455 @vrindex TAR_VOLUME, to-command environment
5457 Ordinal number of the volume @command{tar} is processing.
5459 @vrindex TAR_FORMAT, to-command environment
5461 Format of the archive being processed. @xref{Formats}, for a complete
5462 list of archive format names.
5465 If @var{command} exits with a non-0 status, @command{tar} will print
5466 an error message similar to the following:
5469 tar: 2345: Child returned status 1
5472 Here, @samp{2345} is the PID of the finished process.
5474 If this behavior is not wanted, use @option{--ignore-command-error}:
5477 @opindex ignore-command-error
5478 @item --ignore-command-error
5479 Ignore exit codes of subprocesses. Notice that if the program
5480 exits on signal or otherwise terminates abnormally, the error message
5481 will be printed even if this option is used.
5483 @opindex no-ignore-command-error
5484 @item --no-ignore-command-error
5485 Cancel the effect of any previous @option{--ignore-command-error}
5486 option. This option is useful if you have set
5487 @option{--ignore-command-error} in @env{TAR_OPTIONS}
5488 (@pxref{TAR_OPTIONS}) and wish to temporarily cancel it.
5492 @unnumberedsubsubsec Removing Files
5494 @FIXME{The section is too terse. Something more to add? An example,
5498 @opindex remove-files
5499 @item --remove-files
5500 Remove files after adding them to the archive.
5504 @subsection Coping with Scarce Resources
5507 @cindex Small memory
5508 @cindex Running out of space
5516 @unnumberedsubsubsec Starting File
5519 @opindex starting-file
5520 @item --starting-file=@var{name}
5521 @itemx -K @var{name}
5522 Starts an operation in the middle of an archive. Use in conjunction
5523 with @option{--extract} (@option{--get}, @option{-x}) or @option{--list} (@option{-t}).
5526 @cindex Middle of the archive, starting in the
5527 If a previous attempt to extract files failed due to lack of disk
5528 space, you can use @option{--starting-file=@var{name}} (@option{-K
5529 @var{name}}) to start extracting only after member @var{name} of the
5530 archive. This assumes, of course, that there is now free space, or
5531 that you are now extracting into a different file system. (You could
5532 also choose to suspend @command{tar}, remove unnecessary files from
5533 the file system, and then restart the same @command{tar} operation.
5534 In this case, @option{--starting-file} is not necessary.
5535 @xref{Incremental Dumps}, @xref{interactive}, and @ref{exclude}.)
5538 @unnumberedsubsubsec Same Order
5541 @cindex Large lists of file names on small machines
5543 @opindex preserve-order
5545 @itemx --preserve-order
5547 To process large lists of file names on machines with small amounts of
5548 memory. Use in conjunction with @option{--compare} (@option{--diff},
5549 @option{-d}), @option{--list} (@option{-t}) or @option{--extract}
5550 (@option{--get}, @option{-x}).
5553 The @option{--same-order} (@option{--preserve-order}, @option{-s}) option tells @command{tar} that the list of file
5554 names to be listed or extracted is sorted in the same order as the
5555 files in the archive. This allows a large list of names to be used,
5556 even on a small machine that would not otherwise be able to hold all
5557 the names in memory at the same time. Such a sorted list can easily be
5558 created by running @samp{tar -t} on the archive and editing its output.
5560 This option is probably never needed on modern computer systems.
5563 @section Backup options
5565 @cindex backup options
5567 @GNUTAR{} offers options for making backups of files
5568 before writing new versions. These options control the details of
5569 these backups. They may apply to the archive itself before it is
5570 created or rewritten, as well as individual extracted members. Other
5571 @acronym{GNU} programs (@command{cp}, @command{install}, @command{ln},
5572 and @command{mv}, for example) offer similar options.
5574 Backup options may prove unexpectedly useful when extracting archives
5575 containing many members having identical name, or when extracting archives
5576 on systems having file name limitations, making different members appear
5577 as having similar names through the side-effect of name truncation.
5578 @FIXME{This is true only if we have a good scheme for truncated backup names,
5579 which I'm not sure at all: I suspect work is needed in this area.}
5580 When any existing file is backed up before being overwritten by extraction,
5581 then clashing files are automatically be renamed to be unique, and the
5582 true name is kept for only the last file of a series of clashing files.
5583 By using verbose mode, users may track exactly what happens.
5585 At the detail level, some decisions are still experimental, and may
5586 change in the future, we are waiting comments from our users. So, please
5587 do not learn to depend blindly on the details of the backup features.
5588 For example, currently, directories themselves are never renamed through
5589 using these options, so, extracting a file over a directory still has
5590 good chances to fail. Also, backup options apply to created archives,
5591 not only to extracted members. For created archives, backups will not
5592 be attempted when the archive is a block or character device, or when it
5593 refers to a remote file.
5595 For the sake of simplicity and efficiency, backups are made by renaming old
5596 files prior to creation or extraction, and not by copying. The original
5597 name is restored if the file creation fails. If a failure occurs after a
5598 partial extraction of a file, both the backup and the partially extracted
5602 @item --backup[=@var{method}]
5604 @vindex VERSION_CONTROL
5606 Back up files that are about to be overwritten or removed.
5607 Without this option, the original versions are destroyed.
5609 Use @var{method} to determine the type of backups made.
5610 If @var{method} is not specified, use the value of the @env{VERSION_CONTROL}
5611 environment variable. And if @env{VERSION_CONTROL} is not set,
5612 use the @samp{existing} method.
5614 @vindex version-control @r{Emacs variable}
5615 This option corresponds to the Emacs variable @samp{version-control};
5616 the same values for @var{method} are accepted as in Emacs. This option
5617 also allows more descriptive names. The valid @var{method}s are:
5622 @cindex numbered @r{backup method}
5623 Always make numbered backups.
5627 @cindex existing @r{backup method}
5628 Make numbered backups of files that already have them, simple backups
5633 @cindex simple @r{backup method}
5634 Always make simple backups.
5638 @item --suffix=@var{suffix}
5640 @cindex backup suffix
5641 @vindex SIMPLE_BACKUP_SUFFIX
5642 Append @var{suffix} to each backup file made with @option{--backup}. If this
5643 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
5644 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
5645 set, the default is @samp{~}, just as in Emacs.
5650 @section Notable @command{tar} Usages
5653 @FIXME{Using Unix file linking capability to recreate directory
5654 structures---linking files into one subdirectory and then
5655 @command{tar}ring that directory.}
5657 @FIXME{Nice hairy example using absolute-names, newer, etc.}
5660 You can easily use archive files to transport a group of files from
5661 one system to another: put all relevant files into an archive on one
5662 computer system, transfer the archive to another system, and extract
5663 the contents there. The basic transfer medium might be magnetic tape,
5664 Internet FTP, or even electronic mail (though you must encode the
5665 archive with @command{uuencode} in order to transport it properly by
5666 mail). Both machines do not have to use the same operating system, as
5667 long as they both support the @command{tar} program.
5669 For example, here is how you might copy a directory's contents from
5670 one disk to another, while preserving the dates, modes, owners and
5671 link-structure of all the files therein. In this case, the transfer
5672 medium is a @dfn{pipe}, which is one a Unix redirection mechanism:
5675 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)}
5679 You can avoid subshells by using @option{-C} option:
5682 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xf -}
5686 The command also works using short option forms:
5689 $ @kbd{(cd sourcedir; tar --create --file=- . ) \
5690 | (cd targetdir; tar --extract --file=-)}
5692 $ @kbd{tar --directory sourcedir --create --file=- . ) \
5693 | tar --directory targetdir --extract --file=-}
5697 This is one of the easiest methods to transfer a @command{tar} archive.
5700 @section Looking Ahead: The Rest of this Manual
5702 You have now seen how to use all eight of the operations available to
5703 @command{tar}, and a number of the possible options. The next chapter
5704 explains how to choose and change file and archive names, how to use
5705 files to store names of other files which you can then call as
5706 arguments to @command{tar} (this can help you save time if you expect to
5707 archive the same list of files a number of times), and so forth.
5708 @FIXME{in case it's not obvious, i'm making this up in some sense
5709 based on my limited memory of what the next chapter *really* does. i
5710 just wanted to flesh out this final section a little bit so i'd
5711 remember to stick it in here. :-)}
5713 If there are too many files to conveniently list on the command line,
5714 you can list the names in a file, and @command{tar} will read that file.
5717 There are various ways of causing @command{tar} to skip over some files,
5718 and not archive them. @xref{Choosing}.
5721 @chapter Performing Backups and Restoring Files
5724 @GNUTAR{} is distributed along with the scripts for performing backups
5725 and restores. Even if there is a good chance those scripts may be
5726 satisfying to you, they are not the only scripts or methods available for doing
5727 backups and restore. You may well create your own, or use more
5728 sophisticated packages dedicated to that purpose.
5730 Some users are enthusiastic about @code{Amanda} (The Advanced Maryland
5731 Automatic Network Disk Archiver), a backup system developed by James
5732 da Silva @file{jds@@cs.umd.edu} and available on many Unix systems.
5733 This is free software, and it is available from @uref{http://www.amanda.org}.
5737 Here is a possible plan for a future documentation about the backuping
5738 scripts which are provided within the @GNUTAR{}
5744 @item what are dumps
5745 @item different levels of dumps
5747 @item full dump = dump everything
5748 @item level 1, level 2 dumps etc
5749 A level @var{n} dump dumps everything changed since the last level
5752 @item how to use scripts for dumps (ie, the concept)
5754 @item scripts to run after editing backup specs (details)
5756 @item Backup Specs, what is it.
5758 @item how to customize
5759 @item actual text of script [/sp/dump/backup-specs]
5763 @item rsh doesn't work
5764 @item rtape isn't installed
5767 @item the @option{--incremental} option of tar
5770 @item write protection
5771 @item types of media, different sizes and types, useful for different things
5772 @item files and tape marks
5773 one tape mark between files, two at end.
5774 @item positioning the tape
5775 MT writes two at end of write,
5776 backspaces over one when writing again.
5782 This chapter documents both the provided shell scripts and @command{tar}
5783 options which are more specific to usage as a backup tool.
5785 To @dfn{back up} a file system means to create archives that contain
5786 all the files in that file system. Those archives can then be used to
5787 restore any or all of those files (for instance if a disk crashes or a
5788 file is accidentally deleted). File system @dfn{backups} are also
5792 * Full Dumps:: Using @command{tar} to Perform Full Dumps
5793 * Incremental Dumps:: Using @command{tar} to Perform Incremental Dumps
5794 * Backup Levels:: Levels of Backups
5795 * Backup Parameters:: Setting Parameters for Backups and Restoration
5796 * Scripted Backups:: Using the Backup Scripts
5797 * Scripted Restoration:: Using the Restore Script
5801 @section Using @command{tar} to Perform Full Dumps
5807 @cindex corrupted archives
5808 Full dumps should only be made when no other people or programs
5809 are modifying files in the file system. If files are modified while
5810 @command{tar} is making the backup, they may not be stored properly in
5811 the archive, in which case you won't be able to restore them if you
5812 have to. (Files not being modified are written with no trouble, and do
5813 not corrupt the entire archive.)
5815 You will want to use the @option{--label=@var{archive-label}}
5816 (@option{-V @var{archive-label}}) option to give the archive a
5817 volume label, so you can tell what this archive is even if the label
5818 falls off the tape, or anything like that.
5820 Unless the file system you are dumping is guaranteed to fit on
5821 one volume, you will need to use the @option{--multi-volume} (@option{-M}) option.
5822 Make sure you have enough tapes on hand to complete the backup.
5824 If you want to dump each file system separately you will need to use
5825 the @option{--one-file-system} option to prevent
5826 @command{tar} from crossing file system boundaries when storing
5829 The @option{--incremental} (@option{-G}) (@pxref{Incremental Dumps})
5830 option is not needed, since this is a complete copy of everything in
5831 the file system, and a full restore from this backup would only be
5832 done onto a completely
5835 Unless you are in a hurry, and trust the @command{tar} program (and your
5836 tapes), it is a good idea to use the @option{--verify} (@option{-W})
5837 option, to make sure your files really made it onto the dump properly.
5838 This will also detect cases where the file was modified while (or just
5839 after) it was being archived. Not all media (notably cartridge tapes)
5840 are capable of being verified, unfortunately.
5842 @node Incremental Dumps
5843 @section Using @command{tar} to Perform Incremental Dumps
5845 @dfn{Incremental backup} is a special form of @GNUTAR{} archive that
5846 stores additional metadata so that exact state of the file system
5847 can be restored when extracting the archive.
5849 @GNUTAR{} currently offers two options for handling incremental
5850 backups: @option{--listed-incremental=@var{snapshot-file}} (@option{-g
5851 @var{snapshot-file}}) and @option{--incremental} (@option{-G}).
5853 @xopindex{listed-incremental, described}
5854 The option @option{--listed-incremental} instructs tar to operate on
5855 an incremental archive with additional metadata stored in a standalone
5856 file, called a @dfn{snapshot file}. The purpose of this file is to help
5857 determine which files have been changed, added or deleted since the
5858 last backup, so that the next incremental backup will contain only
5859 modified files. The name of the snapshot file is given as an argument
5863 @item --listed-incremental=@var{file}
5864 @itemx -g @var{file}
5865 Handle incremental backups with snapshot data in @var{file}.
5868 To create an incremental backup, you would use
5869 @option{--listed-incremental} together with @option{--create}
5870 (@pxref{create}). For example:
5873 $ @kbd{tar --create \
5874 --file=archive.1.tar \
5875 --listed-incremental=/var/log/usr.snar \
5879 This will create in @file{archive.1.tar} an incremental backup of
5880 the @file{/usr} file system, storing additional metadata in the file
5881 @file{/var/log/usr.snar}. If this file does not exist, it will be
5882 created. The created archive will then be a @dfn{level 0 backup};
5883 please see the next section for more on backup levels.
5885 Otherwise, if the file @file{/var/log/usr.snar} exists, it
5886 determines which files are modified. In this case only these files will be
5887 stored in the archive. Suppose, for example, that after running the
5888 above command, you delete file @file{/usr/doc/old} and create
5889 directory @file{/usr/local/db} with the following contents:
5892 $ @kbd{ls /usr/local/db}
5897 Some time later you create another incremental backup. You will
5901 $ @kbd{tar --create \
5902 --file=archive.2.tar \
5903 --listed-incremental=/var/log/usr.snar \
5905 tar: usr/local/db: Directory is new
5912 The created archive @file{archive.2.tar} will contain only these
5913 three members. This archive is called a @dfn{level 1 backup}. Notice
5914 that @file{/var/log/usr.snar} will be updated with the new data, so if
5915 you plan to create more @samp{level 1} backups, it is necessary to
5916 create a working copy of the snapshot file before running
5917 @command{tar}. The above example will then be modified as follows:
5920 $ @kbd{cp /var/log/usr.snar /var/log/usr.snar-1}
5921 $ @kbd{tar --create \
5922 --file=archive.2.tar \
5923 --listed-incremental=/var/log/usr.snar-1 \
5928 @xopindex{level, described}
5929 You can force @samp{level 0} backups either by removing the snapshot
5930 file before running @command{tar}, or by supplying the
5931 @option{--level=0} option, e.g.:
5934 $ @kbd{tar --create \
5935 --file=archive.2.tar \
5936 --listed-incremental=/var/log/usr.snar-0 \
5941 Incremental dumps depend crucially on time stamps, so the results are
5942 unreliable if you modify a file's time stamps during dumping (e.g.,
5943 with the @option{--atime-preserve=replace} option), or if you set the clock
5946 @anchor{device numbers}
5947 @cindex Device numbers, using in incremental backups
5948 Metadata stored in snapshot files include device numbers, which,
5949 obviously are supposed to be a non-volatile values. However, it turns
5950 out that @acronym{NFS} devices have undependable values when an automounter
5951 gets in the picture. This can lead to a great deal of spurious
5952 redumping in incremental dumps, so it is somewhat useless to compare
5953 two @acronym{NFS} devices numbers over time. The solution implemented
5954 currently is to considers all @acronym{NFS} devices as being equal
5955 when it comes to comparing directories; this is fairly gross, but
5956 there does not seem to be a better way to go.
5958 Apart from using @acronym{NFS}, there are a number of cases where
5959 relying on device numbers can cause spurious redumping of unmodified
5960 files. For example, this occurs when archiving @acronym{LVM} snapshot
5961 volumes. To avoid this, use @option{--no-check-device} option:
5964 @xopindex{no-check-device, described}
5965 @item --no-check-device
5966 Do not rely on device numbers when preparing a list of changed files
5967 for an incremental dump.
5969 @xopindex{check-device, described}
5970 @item --check-device
5971 Use device numbers when preparing a list of changed files
5972 for an incremental dump. This is the default behavior. The purpose
5973 of this option is to undo the effect of the @option{--no-check-device}
5974 if it was given in @env{TAR_OPTIONS} environment variable
5975 (@pxref{TAR_OPTIONS}).
5978 There is also another way to cope with changing device numbers. It is
5979 described in detail in @ref{Fixing Snapshot Files}.
5981 Note that incremental archives use @command{tar} extensions and may
5982 not be readable by non-@acronym{GNU} versions of the @command{tar} program.
5984 @xopindex{listed-incremental, using with @option{--extract}}
5985 @xopindex{extract, using with @option{--listed-incremental}}
5986 To extract from the incremental dumps, use
5987 @option{--listed-incremental} together with @option{--extract}
5988 option (@pxref{extracting files}). In this case, @command{tar} does
5989 not need to access snapshot file, since all the data necessary for
5990 extraction are stored in the archive itself. So, when extracting, you
5991 can give whatever argument to @option{--listed-incremental}, the usual
5992 practice is to use @option{--listed-incremental=/dev/null}.
5993 Alternatively, you can use @option{--incremental}, which needs no
5994 arguments. In general, @option{--incremental} (@option{-G}) can be
5995 used as a shortcut for @option{--listed-incremental} when listing or
5996 extracting incremental backups (for more information, regarding this
5997 option, @pxref{incremental-op}).
5999 When extracting from the incremental backup @GNUTAR{} attempts to
6000 restore the exact state the file system had when the archive was
6001 created. In particular, it will @emph{delete} those files in the file
6002 system that did not exist in their directories when the archive was
6003 created. If you have created several levels of incremental files,
6004 then in order to restore the exact contents the file system had when
6005 the last level was created, you will need to restore from all backups
6006 in turn. Continuing our example, to restore the state of @file{/usr}
6007 file system, one would do@footnote{Notice, that since both archives
6008 were created without @option{-P} option (@pxref{absolute}), these
6009 commands should be run from the root file system.}:
6012 $ @kbd{tar --extract \
6013 --listed-incremental=/dev/null \
6014 --file archive.1.tar}
6015 $ @kbd{tar --extract \
6016 --listed-incremental=/dev/null \
6017 --file archive.2.tar}
6020 To list the contents of an incremental archive, use @option{--list}
6021 (@pxref{list}), as usual. To obtain more information about the
6022 archive, use @option{--listed-incremental} or @option{--incremental}
6023 combined with two @option{--verbose} options@footnote{Two
6024 @option{--verbose} options were selected to avoid breaking usual
6025 verbose listing output (@option{--list --verbose}) when using in
6028 @xopindex{incremental, using with @option{--list}}
6029 @xopindex{listed-incremental, using with @option{--list}}
6030 @xopindex{list, using with @option{--incremental}}
6031 @xopindex{list, using with @option{--listed-incremental}}
6032 Versions of @GNUTAR{} up to 1.15.1 used to dump verbatim binary
6033 contents of the DUMPDIR header (with terminating nulls) when
6034 @option{--incremental} or @option{--listed-incremental} option was
6035 given, no matter what the verbosity level. This behavior, and,
6036 especially, the binary output it produced were considered inconvenient
6037 and were changed in version 1.16}:
6040 @kbd{tar --list --incremental --verbose --verbose archive.tar}
6043 This command will print, for each directory in the archive, the list
6044 of files in that directory at the time the archive was created. This
6045 information is put out in a format which is both human-readable and
6046 unambiguous for a program: each file name is printed as
6053 where @var{x} is a letter describing the status of the file: @samp{Y}
6054 if the file is present in the archive, @samp{N} if the file is not
6055 included in the archive, or a @samp{D} if the file is a directory (and
6056 is included in the archive). @xref{Dumpdir}, for the detailed
6057 description of dumpdirs and status codes. Each such
6058 line is terminated by a newline character. The last line is followed
6059 by an additional newline to indicate the end of the data.
6061 @anchor{incremental-op}The option @option{--incremental} (@option{-G})
6062 gives the same behavior as @option{--listed-incremental} when used
6063 with @option{--list} and @option{--extract} options. When used with
6064 @option{--create} option, it creates an incremental archive without
6065 creating snapshot file. Thus, it is impossible to create several
6066 levels of incremental backups with @option{--incremental} option.
6069 @section Levels of Backups
6071 An archive containing all the files in the file system is called a
6072 @dfn{full backup} or @dfn{full dump}. You could insure your data by
6073 creating a full dump every day. This strategy, however, would waste a
6074 substantial amount of archive media and user time, as unchanged files
6075 are daily re-archived.
6077 It is more efficient to do a full dump only occasionally. To back up
6078 files between full dumps, you can use @dfn{incremental dumps}. A @dfn{level
6079 one} dump archives all the files that have changed since the last full
6082 A typical dump strategy would be to perform a full dump once a week,
6083 and a level one dump once a day. This means some versions of files
6084 will in fact be archived more than once, but this dump strategy makes
6085 it possible to restore a file system to within one day of accuracy by
6086 only extracting two archives---the last weekly (full) dump and the
6087 last daily (level one) dump. The only information lost would be in
6088 files changed or created since the last daily backup. (Doing dumps
6089 more than once a day is usually not worth the trouble).
6091 @GNUTAR{} comes with scripts you can use to do full
6092 and level-one (actually, even level-two and so on) dumps. Using
6093 scripts (shell programs) to perform backups and restoration is a
6094 convenient and reliable alternative to typing out file name lists
6095 and @command{tar} commands by hand.
6097 Before you use these scripts, you need to edit the file
6098 @file{backup-specs}, which specifies parameters used by the backup
6099 scripts and by the restore script. This file is usually located
6100 in @file{/etc/backup} directory. @xref{Backup Parameters}, for its
6101 detailed description. Once the backup parameters are set, you can
6102 perform backups or restoration by running the appropriate script.
6104 The name of the backup script is @code{backup}. The name of the
6105 restore script is @code{restore}. The following sections describe
6106 their use in detail.
6108 @emph{Please Note:} The backup and restoration scripts are
6109 designed to be used together. While it is possible to restore files by
6110 hand from an archive which was created using a backup script, and to create
6111 an archive by hand which could then be extracted using the restore script,
6112 it is easier to use the scripts. @xref{Incremental Dumps}, before
6113 making such an attempt.
6115 @node Backup Parameters
6116 @section Setting Parameters for Backups and Restoration
6118 The file @file{backup-specs} specifies backup parameters for the
6119 backup and restoration scripts provided with @command{tar}. You must
6120 edit @file{backup-specs} to fit your system configuration and schedule
6121 before using these scripts.
6123 Syntactically, @file{backup-specs} is a shell script, containing
6124 mainly variable assignments. However, any valid shell construct
6125 is allowed in this file. Particularly, you may wish to define
6126 functions within that script (e.g., see @code{RESTORE_BEGIN} below).
6127 For more information about shell script syntax, please refer to
6128 @url{http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
6129 g_02, the definition of the Shell Command Language}. See also
6130 @ref{Top,,Bash Features,bashref,Bash Reference Manual}.
6132 The shell variables controlling behavior of @code{backup} and
6133 @code{restore} are described in the following subsections.
6136 * General-Purpose Variables::
6137 * Magnetic Tape Control::
6139 * backup-specs example:: An Example Text of @file{Backup-specs}
6142 @node General-Purpose Variables
6143 @subsection General-Purpose Variables
6145 @defvr {Backup variable} ADMINISTRATOR
6146 The user name of the backup administrator. @code{Backup} scripts
6147 sends a backup report to this address.
6150 @defvr {Backup variable} BACKUP_HOUR
6151 The hour at which the backups are done. This can be a number from 0
6152 to 23, or the time specification in form @var{hours}:@var{minutes},
6153 or the string @samp{now}.
6155 This variable is used by @code{backup}. Its value may be overridden
6156 using @option{--time} option (@pxref{Scripted Backups}).
6159 @defvr {Backup variable} TAPE_FILE
6161 The device @command{tar} writes the archive to. If @var{TAPE_FILE}
6162 is a remote archive (@pxref{remote-dev}), backup script will suppose
6163 that your @command{mt} is able to access remote devices. If @var{RSH}
6164 (@pxref{RSH}) is set, @option{--rsh-command} option will be added to
6165 invocations of @command{mt}.
6168 @defvr {Backup variable} BLOCKING
6170 The blocking factor @command{tar} will use when writing the dump archive.
6171 @xref{Blocking Factor}.
6174 @defvr {Backup variable} BACKUP_DIRS
6176 A list of file systems to be dumped (for @code{backup}), or restored
6177 (for @code{restore}). You can include any directory
6178 name in the list --- subdirectories on that file system will be
6179 included, regardless of how they may look to other networked machines.
6180 Subdirectories on other file systems will be ignored.
6182 The host name specifies which host to run @command{tar} on, and should
6183 normally be the host that actually contains the file system. However,
6184 the host machine must have @GNUTAR{} installed, and
6185 must be able to access the directory containing the backup scripts and
6186 their support files using the same file name that is used on the
6187 machine where the scripts are run (i.e., what @command{pwd} will print
6188 when in that directory on that machine). If the host that contains
6189 the file system does not have this capability, you can specify another
6190 host as long as it can access the file system through @acronym{NFS}.
6192 If the list of file systems is very long you may wish to put it
6193 in a separate file. This file is usually named
6194 @file{/etc/backup/dirs}, but this name may be overridden in
6195 @file{backup-specs} using @code{DIRLIST} variable.
6198 @defvr {Backup variable} DIRLIST
6200 The name of the file that contains a list of file systems to backup
6201 or restore. By default it is @file{/etc/backup/dirs}.
6204 @defvr {Backup variable} BACKUP_FILES
6206 A list of individual files to be dumped (for @code{backup}), or restored
6207 (for @code{restore}). These should be accessible from the machine on
6208 which the backup script is run.
6210 If the list of file systems is very long you may wish to store it
6211 in a separate file. This file is usually named
6212 @file{/etc/backup/files}, but this name may be overridden in
6213 @file{backup-specs} using @code{FILELIST} variable.
6216 @defvr {Backup variable} FILELIST
6218 The name of the file that contains a list of individual files to backup
6219 or restore. By default it is @file{/etc/backup/files}.
6222 @defvr {Backup variable} MT
6224 Full file name of @command{mt} binary.
6227 @defvr {Backup variable} RSH
6229 Full file name of @command{rsh} binary or its equivalent. You may wish to
6230 set it to @code{ssh}, to improve security. In this case you will have
6231 to use public key authentication.
6234 @defvr {Backup variable} RSH_COMMAND
6236 Full file name of @command{rsh} binary on remote machines. This will
6237 be passed via @option{--rsh-command} option to the remote invocation
6241 @defvr {Backup variable} VOLNO_FILE
6243 Name of temporary file to hold volume numbers. This needs to be accessible
6244 by all the machines which have file systems to be dumped.
6247 @defvr {Backup variable} XLIST
6249 Name of @dfn{exclude file list}. An @dfn{exclude file list} is a file
6250 located on the remote machine and containing the list of files to
6251 be excluded from the backup. Exclude file lists are searched in
6252 /etc/tar-backup directory. A common use for exclude file lists
6253 is to exclude files containing security-sensitive information
6254 (e.g., @file{/etc/shadow} from backups).
6256 This variable affects only @code{backup}.
6259 @defvr {Backup variable} SLEEP_TIME
6261 Time to sleep between dumps of any two successive file systems
6263 This variable affects only @code{backup}.
6266 @defvr {Backup variable} DUMP_REMIND_SCRIPT
6268 Script to be run when it's time to insert a new tape in for the next
6269 volume. Administrators may want to tailor this script for their site.
6270 If this variable isn't set, @GNUTAR{} will display its built-in
6271 prompt, and will expect confirmation from the console. For the
6272 description of the default prompt, see @ref{change volume prompt}.
6276 @defvr {Backup variable} SLEEP_MESSAGE
6278 Message to display on the terminal while waiting for dump time. Usually
6279 this will just be some literal text.
6282 @defvr {Backup variable} TAR
6284 Full file name of the @GNUTAR{} executable. If this is not set, backup
6285 scripts will search @command{tar} in the current shell path.
6288 @node Magnetic Tape Control
6289 @subsection Magnetic Tape Control
6291 Backup scripts access tape device using special @dfn{hook functions}.
6292 These functions take a single argument -- the name of the tape
6293 device. Their names are kept in the following variables:
6295 @defvr {Backup variable} MT_BEGIN
6296 The name of @dfn{begin} function. This function is called before
6297 accessing the drive. By default it retensions the tape:
6303 mt -f "$1" retension
6308 @defvr {Backup variable} MT_REWIND
6309 The name of @dfn{rewind} function. The default definition is as
6322 @defvr {Backup variable} MT_OFFLINE
6323 The name of the function switching the tape off line. By default
6324 it is defined as follows:
6327 MT_OFFLINE=mt_offline
6335 @defvr {Backup variable} MT_STATUS
6336 The name of the function used to obtain the status of the archive device,
6337 including error count. Default definition:
6349 @subsection User Hooks
6351 @dfn{User hooks} are shell functions executed before and after
6352 each @command{tar} invocation. Thus, there are @dfn{backup
6353 hooks}, which are executed before and after dumping each file
6354 system, and @dfn{restore hooks}, executed before and
6355 after restoring a file system. Each user hook is a shell function
6356 taking four arguments:
6358 @deffn {User Hook Function} hook @var{level} @var{host} @var{fs} @var{fsname}
6363 Current backup or restore level.
6366 Name or IP address of the host machine being dumped or restored.
6369 Full file name of the file system being dumped or restored.
6372 File system name with directory separators replaced with colons. This
6373 is useful, e.g., for creating unique files.
6377 Following variables keep the names of user hook functions
6379 @defvr {Backup variable} DUMP_BEGIN
6380 Dump begin function. It is executed before dumping the file system.
6383 @defvr {Backup variable} DUMP_END
6384 Executed after dumping the file system.
6387 @defvr {Backup variable} RESTORE_BEGIN
6388 Executed before restoring the file system.
6391 @defvr {Backup variable} RESTORE_END
6392 Executed after restoring the file system.
6395 @node backup-specs example
6396 @subsection An Example Text of @file{Backup-specs}
6398 The following is an example of @file{backup-specs}:
6401 # site-specific parameters for file system backup.
6403 ADMINISTRATOR=friedman
6405 TAPE_FILE=/dev/nrsmt0
6407 # Use @code{ssh} instead of the less secure @code{rsh}
6409 RSH_COMMAND=/usr/bin/ssh
6411 # Override MT_STATUS function:
6417 # Disable MT_OFFLINE function
6434 apple-gunkies:/com/mailer/gnu
6435 apple-gunkies:/com/archive/gnu"
6437 BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
6441 @node Scripted Backups
6442 @section Using the Backup Scripts
6444 The syntax for running a backup script is:
6447 backup --level=@var{level} --time=@var{time}
6450 The @option{level} option requests the dump level. Thus, to produce
6451 a full dump, specify @code{--level=0} (this is the default, so
6452 @option{--level} may be omitted if its value is @code{0}).
6453 @footnote{For backward compatibility, the @code{backup} will also
6454 try to deduce the requested dump level from the name of the
6455 script itself. If the name consists of a string @samp{level-}
6456 followed by a single decimal digit, that digit is taken as
6457 the dump level number. Thus, you may create a link from @code{backup}
6458 to @code{level-1} and then run @code{level-1} whenever you need to
6459 create a level one dump.}
6461 The @option{--time} option determines when should the backup be
6462 run. @var{Time} may take three forms:
6465 @item @var{hh}:@var{mm}
6467 The dump must be run at @var{hh} hours @var{mm} minutes.
6471 The dump must be run at @var{hh} hours
6475 The dump must be run immediately.
6478 You should start a script with a tape or disk mounted. Once you
6479 start a script, it prompts you for new tapes or disks as it
6480 needs them. Media volumes don't have to correspond to archive
6481 files --- a multi-volume archive can be started in the middle of a
6482 tape that already contains the end of another multi-volume archive.
6483 The @code{restore} script prompts for media by its archive volume,
6484 so to avoid an error message you should keep track of which tape
6485 (or disk) contains which volume of the archive (@pxref{Scripted
6488 The backup scripts write two files on the file system. The first is a
6489 record file in @file{/etc/tar-backup/}, which is used by the scripts
6490 to store and retrieve information about which files were dumped. This
6491 file is not meant to be read by humans, and should not be deleted by
6492 them. @xref{Snapshot Files}, for a more detailed explanation of this
6495 The second file is a log file containing the names of the file systems
6496 and files dumped, what time the backup was made, and any error
6497 messages that were generated, as well as how much space was left in
6498 the media volume after the last volume of the archive was written.
6499 You should check this log file after every backup. The file name is
6500 @file{log-@var{mm-dd-yyyy}-level-@var{n}}, where @var{mm-dd-yyyy}
6501 represents current date, and @var{n} represents current dump level number.
6503 The script also prints the name of each system being dumped to the
6506 Following is the full list of options accepted by @code{backup}
6510 @item -l @var{level}
6511 @itemx --level=@var{level}
6512 Do backup level @var{level} (default 0).
6516 Force backup even if today's log file already exists.
6518 @item -v[@var{level}]
6519 @itemx --verbose[=@var{level}]
6520 Set verbosity level. The higher the level is, the more debugging
6521 information will be output during execution. Default @var{level}
6522 is 100, which means the highest debugging level.
6524 @item -t @var{start-time}
6525 @itemx --time=@var{start-time}
6526 Wait till @var{time}, then do backup.
6530 Display short help message and exit.
6534 Display information about the program's name, version, origin and legal
6535 status, all on standard output, and then exit successfully.
6539 @node Scripted Restoration
6540 @section Using the Restore Script
6542 To restore files that were archived using a scripted backup, use the
6543 @code{restore} script. Its usage is quite straightforward. In the
6544 simplest form, invoke @code{restore --all}, it will
6545 then restore all the file systems and files specified in
6546 @file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
6548 You may select the file systems (and/or files) to restore by
6549 giving @code{restore} list of @dfn{patterns} in its command
6550 line. For example, running
6557 will restore all file systems on the machine @samp{albert}. A more
6558 complicated example:
6561 restore 'albert:*' '*:/var'
6565 This command will restore all file systems on the machine @samp{albert}
6566 as well as @file{/var} file system on all machines.
6568 By default @code{restore} will start restoring files from the lowest
6569 available dump level (usually zero) and will continue through
6570 all available dump levels. There may be situations where such a
6571 thorough restore is not necessary. For example, you may wish to
6572 restore only files from the recent level one backup. To do so,
6573 use @option{--level} option, as shown in the example below:
6579 The full list of options accepted by @code{restore} follows:
6584 Restore all file systems and files specified in @file{backup-specs}
6586 @item -l @var{level}
6587 @itemx --level=@var{level}
6588 Start restoring from the given backup level, instead of the default 0.
6590 @item -v[@var{level}]
6591 @itemx --verbose[=@var{level}]
6592 Set verbosity level. The higher the level is, the more debugging
6593 information will be output during execution. Default @var{level}
6594 is 100, which means the highest debugging level.
6598 Display short help message and exit.
6602 Display information about the program's name, version, origin and legal
6603 status, all on standard output, and then exit successfully.
6606 You should start the restore script with the media containing the
6607 first volume of the archive mounted. The script will prompt for other
6608 volumes as they are needed. If the archive is on tape, you don't need
6609 to rewind the tape to to its beginning---if the tape head is
6610 positioned past the beginning of the archive, the script will rewind
6611 the tape as needed. @xref{Tape Positioning}, for a discussion of tape
6615 @strong{Warning:} The script will delete files from the active file
6616 system if they were not in the file system when the archive was made.
6619 @xref{Incremental Dumps}, for an explanation of how the script makes
6623 @chapter Choosing Files and Names for @command{tar}
6625 Certain options to @command{tar} enable you to specify a name for your
6626 archive. Other options let you decide which files to include or exclude
6627 from the archive, based on when or whether files were modified, whether
6628 the file names do or don't match specified patterns, or whether files
6629 are in specified directories.
6631 This chapter discusses these options in detail.
6634 * file:: Choosing the Archive's Name
6635 * Selecting Archive Members::
6636 * files:: Reading Names from a File
6637 * exclude:: Excluding Some Files
6638 * wildcards:: Wildcards Patterns and Matching
6639 * quoting styles:: Ways of Quoting Special Characters in Names
6640 * transform:: Modifying File and Member Names
6641 * after:: Operating Only on New Files
6642 * recurse:: Descending into Directories
6643 * one:: Crossing File System Boundaries
6647 @section Choosing and Naming Archive Files
6649 @cindex Naming an archive
6650 @cindex Archive Name
6651 @cindex Choosing an archive file
6652 @cindex Where is the archive?
6654 By default, @command{tar} uses an archive file name that was compiled when
6655 it was built on the system; usually this name refers to some physical
6656 tape drive on the machine. However, the person who installed @command{tar}
6657 on the system may not have set the default to a meaningful value as far as
6658 most users are concerned. As a result, you will usually want to tell
6659 @command{tar} where to find (or create) the archive. The
6660 @option{--file=@var{archive-name}} (@option{-f @var{archive-name}})
6661 option allows you to either specify or name a file to use as the archive
6662 instead of the default archive file location.
6665 @xopindex{file, short description}
6666 @item --file=@var{archive-name}
6667 @itemx -f @var{archive-name}
6668 Name the archive to create or operate on. Use in conjunction with
6672 For example, in this @command{tar} command,
6675 $ @kbd{tar -cvf collection.tar blues folk jazz}
6679 @file{collection.tar} is the name of the archive. It must directly
6680 follow the @option{-f} option, since whatever directly follows @option{-f}
6681 @emph{will} end up naming the archive. If you neglect to specify an
6682 archive name, you may end up overwriting a file in the working directory
6683 with the archive you create since @command{tar} will use this file's name
6684 for the archive name.
6686 An archive can be saved as a file in the file system, sent through a
6687 pipe or over a network, or written to an I/O device such as a tape,
6688 floppy disk, or CD write drive.
6690 @cindex Writing new archives
6691 @cindex Archive creation
6692 If you do not name the archive, @command{tar} uses the value of the
6693 environment variable @env{TAPE} as the file name for the archive. If
6694 that is not available, @command{tar} uses a default, compiled-in archive
6695 name, usually that for tape unit zero (i.e., @file{/dev/tu00}).
6697 @cindex Standard input and output
6698 @cindex tar to standard input and output
6699 If you use @file{-} as an @var{archive-name}, @command{tar} reads the
6700 archive from standard input (when listing or extracting files), or
6701 writes it to standard output (when creating an archive). If you use
6702 @file{-} as an @var{archive-name} when modifying an archive,
6703 @command{tar} reads the original archive from its standard input and
6704 writes the entire new archive to its standard output.
6706 The following example is a convenient way of copying directory
6707 hierarchy from @file{sourcedir} to @file{targetdir}.
6710 $ @kbd{(cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)}
6713 The @option{-C} option allows to avoid using subshells:
6716 $ @kbd{tar -C sourcedir -cf - . | tar -C targetdir -xpf -}
6719 In both examples above, the leftmost @command{tar} invocation archives
6720 the contents of @file{sourcedir} to the standard output, while the
6721 rightmost one reads this archive from its standard input and
6722 extracts it. The @option{-p} option tells it to restore permissions
6723 of the extracted files.
6725 @cindex Remote devices
6726 @cindex tar to a remote device
6728 To specify an archive file on a device attached to a remote machine,
6732 @kbd{--file=@var{hostname}:/@var{dev}/@var{file-name}}
6736 @command{tar} will complete the remote connection, if possible, and
6737 prompt you for a username and password. If you use
6738 @option{--file=@@@var{hostname}:/@var{dev}/@var{file-name}}, @command{tar}
6739 will complete the remote connection, if possible, using your username
6740 as the username on the remote machine.
6742 @cindex Local and remote archives
6743 @anchor{local and remote archives}
6744 If the archive file name includes a colon (@samp{:}), then it is assumed
6745 to be a file on another machine. If the archive file is
6746 @samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the
6747 host @var{host}. The remote host is accessed using the @command{rsh}
6748 program, with a username of @var{user}. If the username is omitted
6749 (along with the @samp{@@} sign), then your user name will be used.
6750 (This is the normal @command{rsh} behavior.) It is necessary for the
6751 remote machine, in addition to permitting your @command{rsh} access, to
6752 have the @file{rmt} program installed (This command is included in
6753 the @GNUTAR{} distribution and by default is installed under
6754 @file{@var{prefix}/libexec/rmt}, were @var{prefix} means your
6755 installation prefix). If you need to use a file whose name includes a
6756 colon, then the remote tape drive behavior
6757 can be inhibited by using the @option{--force-local} option.
6759 When the archive is being created to @file{/dev/null}, @GNUTAR{}
6760 tries to minimize input and output operations. The Amanda backup
6761 system, when used with @GNUTAR{}, has an initial sizing pass which
6764 @node Selecting Archive Members
6765 @section Selecting Archive Members
6766 @cindex Specifying files to act on
6767 @cindex Specifying archive members
6769 @dfn{File Name arguments} specify which files in the file system
6770 @command{tar} operates on, when creating or adding to an archive, or which
6771 archive members @command{tar} operates on, when reading or deleting from
6772 an archive. @xref{Operations}.
6774 To specify file names, you can include them as the last arguments on
6775 the command line, as follows:
6777 @kbd{tar} @var{operation} [@var{option1} @var{option2} @dots{}] [@var{file name-1} @var{file name-2} @dots{}]
6780 If a file name begins with dash (@samp{-}), precede it with
6781 @option{--add-file} option to prevent it from being treated as an
6784 @anchor{input name quoting}
6785 By default @GNUTAR{} attempts to @dfn{unquote} each file or member
6786 name, replacing @dfn{escape sequences} according to the following
6789 @multitable @columnfractions 0.20 0.60
6790 @headitem Escape @tab Replaced with
6791 @item \a @tab Audible bell (@acronym{ASCII} 7)
6792 @item \b @tab Backspace (@acronym{ASCII} 8)
6793 @item \f @tab Form feed (@acronym{ASCII} 12)
6794 @item \n @tab New line (@acronym{ASCII} 10)
6795 @item \r @tab Carriage return (@acronym{ASCII} 13)
6796 @item \t @tab Horizontal tabulation (@acronym{ASCII} 9)
6797 @item \v @tab Vertical tabulation (@acronym{ASCII} 11)
6798 @item \? @tab @acronym{ASCII} 127
6799 @item \@var{n} @tab @acronym{ASCII} @var{n} (@var{n} should be an octal number
6803 A backslash followed by any other symbol is retained.
6805 This default behavior is controlled by the following command line
6811 Enable unquoting input file or member names (default).
6815 Disable unquoting input file or member names.
6818 If you specify a directory name as a file name argument, all the files
6819 in that directory are operated on by @command{tar}.
6821 If you do not specify files, @command{tar} behavior differs depending
6822 on the operation mode as described below:
6824 When @command{tar} is invoked with @option{--create} (@option{-c}),
6825 @command{tar} will stop immediately, reporting the following:
6829 $ @kbd{tar cf a.tar}
6830 tar: Cowardly refusing to create an empty archive
6831 Try `tar --help' or `tar --usage' for more information.
6835 If you specify either @option{--list} (@option{-t}) or
6836 @option{--extract} (@option{--get}, @option{-x}), @command{tar}
6837 operates on all the archive members in the archive.
6839 If run with @option{--diff} option, tar will compare the archive with
6840 the contents of the current working directory.
6842 If you specify any other operation, @command{tar} does nothing.
6844 By default, @command{tar} takes file names from the command line. However,
6845 there are other ways to specify file or member names, or to modify the
6846 manner in which @command{tar} selects the files or members upon which to
6847 operate. In general, these methods work both for specifying the names
6848 of files and archive members.
6851 @section Reading Names from a File
6853 @cindex Reading file names from a file
6854 @cindex Lists of file names
6855 @cindex File Name arguments, alternatives
6856 @cindex @command{find}, using with @command{tar}
6857 Instead of giving the names of files or archive members on the command
6858 line, you can put the names into a file, and then use the
6859 @option{--files-from=@var{file-of-names}} (@option{-T
6860 @var{file-of-names}}) option to @command{tar}. Give the name of the
6861 file which contains the list of files to include as the argument to
6862 @option{--files-from}. In the list, the file names should be separated by
6863 newlines. You will frequently use this option when you have generated
6864 the list of files to archive with the @command{find} utility.
6868 @item --files-from=@var{file-name}
6869 @itemx -T @var{file-name}
6870 Get names to extract or create from file @var{file-name}.
6873 If you give a single dash as a file name for @option{--files-from}, (i.e.,
6874 you specify either @code{--files-from=-} or @code{-T -}), then the file
6875 names are read from standard input.
6877 Unless you are running @command{tar} with @option{--create}, you can not use
6878 both @code{--files-from=-} and @code{--file=-} (@code{-f -}) in the same
6881 Any number of @option{-T} options can be given in the command line.
6883 The following example shows how to use @command{find} to generate a list of
6884 files smaller than 400K in length and put that list into a file
6885 called @file{small-files}. You can then use the @option{-T} option to
6886 @command{tar} to specify the files from that file, @file{small-files}, to
6887 create the archive @file{little.tgz}. (The @option{-z} option to
6888 @command{tar} compresses the archive with @command{gzip}; @pxref{gzip} for
6892 $ @kbd{find . -size -400 -print > small-files}
6893 $ @kbd{tar -c -v -z -T small-files -f little.tgz}
6897 In the file list given by @option{-T} option, any file name beginning
6898 with @samp{-} character is considered a @command{tar} option and is
6899 processed accordingly.@footnote{Versions of @GNUTAR{} up to 1.15.1
6900 recognized only @option{-C} option in file lists, and only if the
6901 option and its argument occupied two consecutive lines.} For example,
6902 the common use of this feature is to change to another directory by
6903 specifying @option{-C} option:
6913 $ @kbd{tar -c -f foo.tar --files-from list}
6918 In this example, @command{tar} will first switch to @file{/etc}
6919 directory and add files @file{passwd} and @file{hosts} to the
6920 archive. Then it will change to @file{/lib} directory and will archive
6921 the file @file{libc.a}. Thus, the resulting archive @file{foo.tar} will
6926 $ @kbd{tar tf foo.tar}
6934 @xopindex{directory, using in @option{--files-from} argument}
6935 Notice that the option parsing algorithm used with @option{-T} is
6936 stricter than the one used by shell. Namely, when specifying option
6937 arguments, you should observe the following rules:
6941 When using short (single-letter) option form, its argument must
6942 immediately follow the option letter, without any intervening
6943 whitespace. For example: @code{-Cdir}.
6946 When using long option form, the option argument must be separated
6947 from the option by a single equal sign. No whitespace is allowed on
6948 any side of the equal sign. For example: @code{--directory=dir}.
6951 For both short and long option forms, the option argument can be given
6952 on the next line after the option name, e.g.:
6973 If you happen to have a file whose name starts with @samp{-},
6974 precede it with @option{--add-file} option to prevent it from
6975 being recognized as an option. For example: @code{--add-file=--my-file}.
6982 @subsection @code{NUL} Terminated File Names
6984 @cindex File names, terminated by @code{NUL}
6985 @cindex @code{NUL} terminated file names
6986 The @option{--null} option causes
6987 @option{--files-from=@var{file-of-names}} (@option{-T @var{file-of-names}})
6988 to read file names terminated by a @code{NUL} instead of a newline, so
6989 files whose names contain newlines can be archived using
6990 @option{--files-from}.
6993 @xopindex{null, described}
6995 Only consider @code{NUL} terminated file names, instead of files that
6996 terminate in a newline.
6998 @xopindex{no-null, described}
7000 Undo the effect of any previous @option{--null} option.
7003 The @option{--null} option is just like the one in @acronym{GNU}
7004 @command{xargs} and @command{cpio}, and is useful with the
7005 @option{-print0} predicate of @acronym{GNU} @command{find}. In
7006 @command{tar}, @option{--null} also disables special handling for
7007 file names that begin with dash.
7009 This example shows how to use @command{find} to generate a list of files
7010 larger than 800K in length and put that list into a file called
7011 @file{long-files}. The @option{-print0} option to @command{find} is just
7012 like @option{-print}, except that it separates files with a @code{NUL}
7013 rather than with a newline. You can then run @command{tar} with both the
7014 @option{--null} and @option{-T} options to specify that @command{tar} get the
7015 files from that file, @file{long-files}, to create the archive
7016 @file{big.tgz}. The @option{--null} option to @command{tar} will cause
7017 @command{tar} to recognize the @code{NUL} separator between files.
7020 $ @kbd{find . -size +800 -print0 > long-files}
7021 $ @kbd{tar -c -v --null --files-from=long-files --file=big.tar}
7024 The @option{--no-null} option can be used if you need to read both
7025 zero-terminated and newline-terminated files on the same command line.
7026 For example, if @file{flist} is a newline-terminated file, then the
7027 following command can be used to combine it with the above command:
7031 $ @kbd{find . -size +800 -print0 |
7032 tar -c -f big.tar --null -T - --no-null -T flist}
7036 This example uses short options for typographic reasons, to avoid
7039 @GNUTAR is able to automatically detect null-terminated file lists, so
7040 it is safe to use them even without the @option{--null} option. In
7041 this case @command{tar} will print a warning and continue reading such
7042 a file as if @option{--null} were actually given:
7046 $ @kbd{find . -size +800 -print0 | tar -c -f big.tar -T -}
7047 tar: -: file name read contains nul character
7051 The null terminator, however, remains in effect only for this
7052 particular file, any following @option{-T} options will assume
7053 newline termination. Of course, the null autodetection applies
7054 to these eventual surplus @option{-T} options as well.
7057 @section Excluding Some Files
7059 @cindex File names, excluding files by
7060 @cindex Excluding files by name and pattern
7061 @cindex Excluding files by file system
7063 @opindex exclude-from
7064 To avoid operating on files whose names match a particular pattern,
7065 use the @option{--exclude} or @option{--exclude-from} options.
7069 @item --exclude=@var{pattern}
7070 Causes @command{tar} to ignore files that match the @var{pattern}.
7074 The @option{--exclude=@var{pattern}} option prevents any file or
7075 member whose name matches the shell wildcard (@var{pattern}) from
7077 For example, to create an archive with all the contents of the directory
7078 @file{src} except for files whose names end in @file{.o}, use the
7079 command @samp{tar -cf src.tar --exclude='*.o' src}.
7081 You may give multiple @option{--exclude} options.
7084 @opindex exclude-from
7085 @item --exclude-from=@var{file}
7086 @itemx -X @var{file}
7087 Causes @command{tar} to ignore files that match the patterns listed in
7091 @findex exclude-from
7092 Use the @option{--exclude-from} option to read a
7093 list of patterns, one per line, from @var{file}; @command{tar} will
7094 ignore files matching those patterns. Thus if @command{tar} is
7095 called as @w{@samp{tar -c -X foo .}} and the file @file{foo} contains a
7096 single line @file{*.o}, no files whose names end in @file{.o} will be
7097 added to the archive.
7099 Notice, that lines from @var{file} are read verbatim. One of the
7100 frequent errors is leaving some extra whitespace after a file name,
7101 which is difficult to catch using text editors.
7103 However, empty lines are OK.
7106 @cindex version control system, excluding files
7107 @cindex VCS, excluding files
7108 @cindex SCCS, excluding files
7109 @cindex RCS, excluding files
7110 @cindex CVS, excluding files
7111 @cindex SVN, excluding files
7112 @cindex git, excluding files
7113 @cindex Bazaar, excluding files
7114 @cindex Arch, excluding files
7115 @cindex Mercurial, excluding files
7116 @cindex Darcs, excluding files
7117 @opindex exclude-vcs
7119 Exclude files and directories used by following version control
7120 systems: @samp{CVS}, @samp{RCS}, @samp{SCCS}, @samp{SVN}, @samp{Arch},
7121 @samp{Bazaar}, @samp{Mercurial}, and @samp{Darcs}.
7123 As of version @value{VERSION}, the following files are excluded:
7126 @item @file{CVS/}, and everything under it
7127 @item @file{RCS/}, and everything under it
7128 @item @file{SCCS/}, and everything under it
7129 @item @file{.git/}, and everything under it
7130 @item @file{.gitignore}
7131 @item @file{.cvsignore}
7132 @item @file{.svn/}, and everything under it
7133 @item @file{.arch-ids/}, and everything under it
7134 @item @file{@{arch@}/}, and everything under it
7135 @item @file{=RELEASE-ID}
7136 @item @file{=meta-update}
7137 @item @file{=update}
7139 @item @file{.bzrignore}
7140 @item @file{.bzrtags}
7142 @item @file{.hgignore}
7143 @item @file{.hgrags}
7147 @opindex exclude-backups
7148 @item --exclude-backups
7149 Exclude backup and lock files. This option causes exclusion of files
7150 that match the following shell globbing patterns:
7160 @findex exclude-caches
7161 When creating an archive, the @option{--exclude-caches} option family
7162 causes @command{tar} to exclude all directories that contain a @dfn{cache
7163 directory tag}. A cache directory tag is a short file with the
7164 well-known name @file{CACHEDIR.TAG} and having a standard header
7165 specified in @url{http://www.brynosaurus.com/cachedir/spec.html}.
7166 Various applications write cache directory tags into directories they
7167 use to hold regenerable, non-precious data, so that such data can be
7168 more easily excluded from backups.
7170 There are three @samp{exclude-caches} options, each providing a different
7171 exclusion semantics:
7174 @opindex exclude-caches
7175 @item --exclude-caches
7176 Do not archive the contents of the directory, but archive the
7177 directory itself and the @file{CACHEDIR.TAG} file.
7179 @opindex exclude-caches-under
7180 @item --exclude-caches-under
7181 Do not archive the contents of the directory, nor the
7182 @file{CACHEDIR.TAG} file, archive only the directory itself.
7184 @opindex exclude-caches-all
7185 @item --exclude-caches-all
7186 Omit directories containing @file{CACHEDIR.TAG} file entirely.
7190 Another option family, @option{--exclude-tag}, provides a generalization of
7191 this concept. It takes a single argument, a file name to look for.
7192 Any directory that contains this file will be excluded from the dump.
7193 Similarly to @samp{exclude-caches}, there are three options in this
7197 @opindex exclude-tag
7198 @item --exclude-tag=@var{file}
7199 Do not dump the contents of the directory, but dump the
7200 directory itself and the @var{file}.
7202 @opindex exclude-tag-under
7203 @item --exclude-tag-under=@var{file}
7204 Do not dump the contents of the directory, nor the
7205 @var{file}, archive only the directory itself.
7207 @opindex exclude-tag-all
7208 @item --exclude-tag-all=@var{file}
7209 Omit directories containing @var{file} file entirely.
7212 Multiple @option{--exclude-tag*} options can be given.
7214 For example, given this directory:
7229 The @option{--exclude-tag} will produce the following:
7232 $ @kbd{tar -cf archive.tar --exclude-tag=tagfile -v dir}
7237 tar: dir/folk/: contains a cache directory tag tagfile;
7242 Both the @file{dir/folk} directory and its tagfile are preserved in
7243 the archive, however the rest of files in this directory are not.
7245 Now, using the @option{--exclude-tag-under} option will exclude
7246 @file{tagfile} from the dump, while still preserving the directory
7247 itself, as shown in this example:
7250 $ @kbd{tar -cf archive.tar --exclude-tag-under=tagfile -v dir}
7255 ./tar: dir/folk/: contains a cache directory tag tagfile;
7259 Finally, using @option{--exclude-tag-all} omits the @file{dir/folk}
7263 $ @kbd{tar -cf archive.tar --exclude-tag-all=tagfile -v dir}
7267 ./tar: dir/folk/: contains a cache directory tag tagfile;
7268 directory not dumped
7272 * problems with exclude::
7275 @node problems with exclude
7276 @unnumberedsubsec Problems with Using the @code{exclude} Options
7278 @xopindex{exclude, potential problems with}
7279 Some users find @samp{exclude} options confusing. Here are some common
7284 The main operating mode of @command{tar} does not act on a file name
7285 explicitly listed on the command line, if one of its file name
7286 components is excluded. In the example above, if
7287 you create an archive and exclude files that end with @samp{*.o}, but
7288 explicitly name the file @samp{dir.o/foo} after all the options have been
7289 listed, @samp{dir.o/foo} will be excluded from the archive.
7292 You can sometimes confuse the meanings of @option{--exclude} and
7293 @option{--exclude-from}. Be careful: use @option{--exclude} when files
7294 to be excluded are given as a pattern on the command line. Use
7295 @option{--exclude-from} to introduce the name of a file which contains
7296 a list of patterns, one per line; each of these patterns can exclude
7297 zero, one, or many files.
7300 When you use @option{--exclude=@var{pattern}}, be sure to quote the
7301 @var{pattern} parameter, so @GNUTAR{} sees wildcard characters
7302 like @samp{*}. If you do not do this, the shell might expand the
7303 @samp{*} itself using files at hand, so @command{tar} might receive a
7304 list of files instead of one pattern, or none at all, making the
7305 command somewhat illegal. This might not correspond to what you want.
7310 $ @kbd{tar -c -f @var{archive.tar} --exclude '*.o' @var{directory}}
7318 $ @kbd{tar -c -f @var{archive.tar} --exclude *.o @var{directory}}
7322 You must use use shell syntax, or globbing, rather than @code{regexp}
7323 syntax, when using exclude options in @command{tar}. If you try to use
7324 @code{regexp} syntax to describe files to be excluded, your command
7328 @FIXME{The change in semantics must have occurred before 1.11,
7329 so I doubt if it is worth mentioning at all. Anyway, should at
7330 least specify in which version the semantics changed.}
7331 In earlier versions of @command{tar}, what is now the
7332 @option{--exclude-from} option was called @option{--exclude} instead.
7333 Now, @option{--exclude} applies to patterns listed on the command
7334 line and @option{--exclude-from} applies to patterns listed in a
7340 @section Wildcards Patterns and Matching
7342 @dfn{Globbing} is the operation by which @dfn{wildcard} characters,
7343 @samp{*} or @samp{?} for example, are replaced and expanded into all
7344 existing files matching the given pattern. @GNUTAR{} can use wildcard
7345 patterns for matching (or globbing) archive members when extracting
7346 from or listing an archive. Wildcard patterns are also used for
7347 verifying volume labels of @command{tar} archives. This section has the
7348 purpose of explaining wildcard syntax for @command{tar}.
7350 @FIXME{the next few paragraphs need work.}
7352 A @var{pattern} should be written according to shell syntax, using wildcard
7353 characters to effect globbing. Most characters in the pattern stand
7354 for themselves in the matched string, and case is significant: @samp{a}
7355 will match only @samp{a}, and not @samp{A}. The character @samp{?} in the
7356 pattern matches any single character in the matched string. The character
7357 @samp{*} in the pattern matches zero, one, or more single characters in
7358 the matched string. The character @samp{\} says to take the following
7359 character of the pattern @emph{literally}; it is useful when one needs to
7360 match the @samp{?}, @samp{*}, @samp{[} or @samp{\} characters, themselves.
7362 The character @samp{[}, up to the matching @samp{]}, introduces a character
7363 class. A @dfn{character class} is a list of acceptable characters
7364 for the next single character of the matched string. For example,
7365 @samp{[abcde]} would match any of the first five letters of the alphabet.
7366 Note that within a character class, all of the ``special characters''
7367 listed above other than @samp{\} lose their special meaning; for example,
7368 @samp{[-\\[*?]]} would match any of the characters, @samp{-}, @samp{\},
7369 @samp{[}, @samp{*}, @samp{?}, or @samp{]}. (Due to parsing constraints,
7370 the characters @samp{-} and @samp{]} must either come @emph{first} or
7371 @emph{last} in a character class.)
7373 @cindex Excluding characters from a character class
7374 @cindex Character class, excluding characters from
7375 If the first character of the class after the opening @samp{[}
7376 is @samp{!} or @samp{^}, then the meaning of the class is reversed.
7377 Rather than listing character to match, it lists those characters which
7378 are @emph{forbidden} as the next single character of the matched string.
7380 Other characters of the class stand for themselves. The special
7381 construction @samp{[@var{a}-@var{e}]}, using an hyphen between two
7382 letters, is meant to represent all characters between @var{a} and
7385 @FIXME{need to add a sentence or so here to make this clear for those
7386 who don't have dan around.}
7388 Periods (@samp{.}) or forward slashes (@samp{/}) are not considered
7389 special for wildcard matches. However, if a pattern completely matches
7390 a directory prefix of a matched string, then it matches the full matched
7391 string: thus, excluding a directory also excludes all the files beneath it.
7394 * controlling pattern-matching::
7397 @node controlling pattern-matching
7398 @unnumberedsubsec Controlling Pattern-Matching
7400 For the purposes of this section, we call @dfn{exclusion members} all
7401 member names obtained while processing @option{--exclude} and
7402 @option{--exclude-from} options, and @dfn{inclusion members} those
7403 member names that were given in the command line or read from the file
7404 specified with @option{--files-from} option.
7406 These two pairs of member lists are used in the following operations:
7407 @option{--diff}, @option{--extract}, @option{--list},
7410 There are no inclusion members in create mode (@option{--create} and
7411 @option{--append}), since in this mode the names obtained from the
7412 command line refer to @emph{files}, not archive members.
7414 By default, inclusion members are compared with archive members
7415 literally @footnote{Notice that earlier @GNUTAR{} versions used
7416 globbing for inclusion members, which contradicted to UNIX98
7417 specification and was not documented. @xref{Changes}, for more
7418 information on this and other changes.} and exclusion members are
7419 treated as globbing patterns. For example:
7423 $ @kbd{tar tf foo.tar}
7428 # @i{Member names are used verbatim:}
7429 $ @kbd{tar -xf foo.tar -v '[remarks]'}
7431 # @i{Exclude member names are globbed:}
7432 $ @kbd{tar -xf foo.tar -v --exclude '*.c'}
7438 This behavior can be altered by using the following options:
7443 Treat all member names as wildcards.
7445 @opindex no-wildcards
7446 @item --no-wildcards
7447 Treat all member names as literal strings.
7450 Thus, to extract files whose names end in @samp{.c}, you can use:
7453 $ @kbd{tar -xf foo.tar -v --wildcards '*.c'}
7459 Notice quoting of the pattern to prevent the shell from interpreting
7462 The effect of @option{--wildcards} option is canceled by
7463 @option{--no-wildcards}. This can be used to pass part of
7464 the command line arguments verbatim and other part as globbing
7465 patterns. For example, the following invocation:
7468 $ @kbd{tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'}
7472 instructs @command{tar} to extract from @file{foo.tar} all files whose
7473 names end in @samp{.txt} and the file named @file{[remarks]}.
7475 Normally, a pattern matches a name if an initial subsequence of the
7476 name's components matches the pattern, where @samp{*}, @samp{?}, and
7477 @samp{[...]} are the usual shell wildcards, @samp{\} escapes wildcards,
7478 and wildcards can match @samp{/}.
7480 Other than optionally stripping leading @samp{/} from names
7481 (@pxref{absolute}), patterns and names are used as-is. For
7482 example, trailing @samp{/} is not trimmed from a user-specified name
7483 before deciding whether to exclude it.
7485 However, this matching procedure can be altered by the options listed
7486 below. These options accumulate. For example:
7489 --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
7493 ignores case when excluding @samp{makefile}, but not when excluding
7498 @opindex no-anchored
7500 @itemx --no-anchored
7501 If anchored, a pattern must match an initial subsequence
7502 of the name's components. Otherwise, the pattern can match any
7503 subsequence. Default is @option{--no-anchored} for exclusion members
7504 and @option{--anchored} inclusion members.
7506 @opindex ignore-case
7507 @opindex no-ignore-case
7509 @itemx --no-ignore-case
7510 When ignoring case, upper-case patterns match lower-case names and vice versa.
7511 When not ignoring case (the default), matching is case-sensitive.
7513 @opindex wildcards-match-slash
7514 @opindex no-wildcards-match-slash
7515 @item --wildcards-match-slash
7516 @itemx --no-wildcards-match-slash
7517 When wildcards match slash (the default for exclusion members), a
7518 wildcard like @samp{*} in the pattern can match a @samp{/} in the
7519 name. Otherwise, @samp{/} is matched only by @samp{/}.
7523 The @option{--recursion} and @option{--no-recursion} options
7524 (@pxref{recurse}) also affect how member patterns are interpreted. If
7525 recursion is in effect, a pattern matches a name if it matches any of
7526 the name's parent directories.
7528 The following table summarizes pattern-matching default values:
7530 @multitable @columnfractions .3 .7
7531 @headitem Members @tab Default settings
7532 @item Inclusion @tab @option{--no-wildcards --anchored --no-wildcards-match-slash}
7533 @item Exclusion @tab @option{--wildcards --no-anchored --wildcards-match-slash}
7536 @node quoting styles
7537 @section Quoting Member Names
7539 When displaying member names, @command{tar} takes care to avoid
7540 ambiguities caused by certain characters. This is called @dfn{name
7541 quoting}. The characters in question are:
7544 @item Non-printable control characters:
7545 @anchor{escape sequences}
7546 @multitable @columnfractions 0.20 0.10 0.60
7547 @headitem Character @tab @acronym{ASCII} @tab Character name
7548 @item \a @tab 7 @tab Audible bell
7549 @item \b @tab 8 @tab Backspace
7550 @item \f @tab 12 @tab Form feed
7551 @item \n @tab 10 @tab New line
7552 @item \r @tab 13 @tab Carriage return
7553 @item \t @tab 9 @tab Horizontal tabulation
7554 @item \v @tab 11 @tab Vertical tabulation
7557 @item Space (@acronym{ASCII} 32)
7559 @item Single and double quotes (@samp{'} and @samp{"})
7561 @item Backslash (@samp{\})
7564 The exact way @command{tar} uses to quote these characters depends on
7565 the @dfn{quoting style}. The default quoting style, called
7566 @dfn{escape} (see below), uses backslash notation to represent control
7567 characters, space and backslash. Using this quoting style, control
7568 characters are represented as listed in column @samp{Character} in the
7569 above table, a space is printed as @samp{\ } and a backslash as @samp{\\}.
7571 @GNUTAR{} offers seven distinct quoting styles, which can be selected
7572 using @option{--quoting-style} option:
7575 @item --quoting-style=@var{style}
7576 @opindex quoting-style
7578 Sets quoting style. Valid values for @var{style} argument are:
7579 literal, shell, shell-always, c, escape, locale, clocale.
7582 These styles are described in detail below. To illustrate their
7583 effect, we will use an imaginary tar archive @file{arch.tar}
7584 containing the following members:
7588 # 1. Contains horizontal tabulation character.
7590 # 2. Contains newline character
7593 # 3. Contains a space
7595 # 4. Contains double quotes
7597 # 5. Contains single quotes
7599 # 6. Contains a backslash character:
7604 Here is how usual @command{ls} command would have listed them, if they
7605 had existed in the current working directory:
7623 No quoting, display each character as is:
7627 $ @kbd{tar tf arch.tar --quoting-style=literal}
7640 Display characters the same way Bourne shell does:
7641 control characters, except @samp{\t} and @samp{\n}, are printed using
7642 backslash escapes, @samp{\t} and @samp{\n} are printed as is, and a
7643 single quote is printed as @samp{\'}. If a name contains any quoted
7644 characters, it is enclosed in single quotes. In particular, if a name
7645 contains single quotes, it is printed as several single-quoted strings:
7649 $ @kbd{tar tf arch.tar --quoting-style=shell}
7652 './a'\''single'\''quote'
7662 Same as @samp{shell}, but the names are always enclosed in single
7667 $ @kbd{tar tf arch.tar --quoting-style=shell-always}
7670 './a'\''single'\''quote'
7680 Use the notation of the C programming language. All names are
7681 enclosed in double quotes. Control characters are quoted using
7682 backslash notations, double quotes are represented as @samp{\"},
7683 backslash characters are represented as @samp{\\}. Single quotes and
7684 spaces are not quoted:
7688 $ @kbd{tar tf arch.tar --quoting-style=c}
7692 "./a\"double\"quote"
7700 Control characters are printed using backslash notation, a space is
7701 printed as @samp{\ } and a backslash as @samp{\\}. This is the
7702 default quoting style, unless it was changed when configured the
7707 $ @kbd{tar tf arch.tar --quoting-style=escape}
7719 Control characters, single quote and backslash are printed using
7720 backslash notation. All names are quoted using left and right
7721 quotation marks, appropriate to the current locale. If it does not
7722 define quotation marks, use @samp{`} as left and @samp{'} as right
7723 quotation marks. Any occurrences of the right quotation mark in a
7724 name are escaped with @samp{\}, for example:
7730 $ @kbd{tar tf arch.tar --quoting-style=locale}
7733 `./a\'single\'quote'
7742 Same as @samp{locale}, but @samp{"} is used for both left and right
7743 quotation marks, if not provided by the currently selected locale:
7747 $ @kbd{tar tf arch.tar --quoting-style=clocale}
7751 "./a\"double\"quote"
7759 You can specify which characters should be quoted in addition to those
7760 implied by the current quoting style:
7763 @item --quote-chars=@var{string}
7764 Always quote characters from @var{string}, even if the selected
7765 quoting style would not quote them.
7768 For example, using @samp{escape} quoting (compare with the usual
7769 escape listing above):
7773 $ @kbd{tar tf arch.tar --quoting-style=escape --quote-chars=' "'}
7784 To disable quoting of such additional characters, use the following
7788 @item --no-quote-chars=@var{string}
7789 Remove characters listed in @var{string} from the list of quoted
7790 characters set by the previous @option{--quote-chars} option.
7793 This option is particularly useful if you have added
7794 @option{--quote-chars} to your @env{TAR_OPTIONS} (@pxref{TAR_OPTIONS})
7795 and wish to disable it for the current invocation.
7797 Note, that @option{--no-quote-chars} does @emph{not} disable those
7798 characters that are quoted by default in the selected quoting style.
7801 @section Modifying File and Member Names
7803 @command{Tar} archives contain detailed information about files stored
7804 in them and full file names are part of that information. When
7805 storing file to an archive, its file name is recorded in it,
7806 along with the actual file contents. When restoring from an archive,
7807 a file is created on disk with exactly the same name as that stored
7808 in the archive. In the majority of cases this is the desired behavior
7809 of a file archiver. However, there are some cases when it is not.
7811 First of all, it is often unsafe to extract archive members with
7812 absolute file names or those that begin with a @file{../}. @GNUTAR{}
7813 takes special precautions when extracting such names and provides a
7814 special option for handling them, which is described in
7817 Secondly, you may wish to extract file names without some leading
7818 directory components, or with otherwise modified names. In other
7819 cases it is desirable to store files under differing names in the
7822 @GNUTAR{} provides several options for these needs.
7825 @opindex strip-components
7826 @item --strip-components=@var{number}
7827 Strip given @var{number} of leading components from file names before
7831 For example, suppose you have archived whole @file{/usr} hierarchy to
7832 a tar archive named @file{usr.tar}. Among other files, this archive
7833 contains @file{usr/include/stdlib.h}, which you wish to extract to
7834 the current working directory. To do so, you type:
7837 $ @kbd{tar -xf usr.tar --strip=2 usr/include/stdlib.h}
7840 The option @option{--strip=2} instructs @command{tar} to strip the
7841 two leading components (@file{usr/} and @file{include/}) off the file
7844 If you add the @option{--verbose} (@option{-v}) option to the invocation
7845 above, you will note that the verbose listing still contains the
7846 full file name, with the two removed components still in place. This
7847 can be inconvenient, so @command{tar} provides a special option for
7848 altering this behavior:
7850 @anchor{show-transformed-names}
7852 @opindex show-transformed-names
7853 @item --show-transformed-names
7854 Display file or member names with all requested transformations
7863 $ @kbd{tar -xf usr.tar -v --strip=2 usr/include/stdlib.h}
7864 usr/include/stdlib.h
7865 $ @kbd{tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h}
7870 Notice that in both cases the file @file{stdlib.h} is extracted to the
7871 current working directory, @option{--show-transformed-names} affects
7872 only the way its name is displayed.
7874 This option is especially useful for verifying whether the invocation
7875 will have the desired effect. Thus, before running
7878 $ @kbd{tar -x --strip=@var{n}}
7882 it is often advisable to run
7885 $ @kbd{tar -t -v --show-transformed --strip=@var{n}}
7889 to make sure the command will produce the intended results.
7891 In case you need to apply more complex modifications to the file name,
7892 @GNUTAR{} provides a general-purpose transformation option:
7897 @item --transform=@var{expression}
7898 @itemx --xform=@var{expression}
7899 Modify file names using supplied @var{expression}.
7903 The @var{expression} is a @command{sed}-like replace expression of the
7907 s/@var{regexp}/@var{replace}/[@var{flags}]
7911 where @var{regexp} is a @dfn{regular expression}, @var{replace} is a
7912 replacement for each file name part that matches @var{regexp}. Both
7913 @var{regexp} and @var{replace} are described in detail in
7914 @ref{The "s" Command, The "s" Command, The `s' Command, sed, GNU sed}.
7916 Any delimiter can be used in lieue of @samp{/}, the only requirement being
7917 that it be used consistently throughout the expression. For example,
7918 the following two expressions are equivalent:
7927 Changing delimiters is often useful when the @var{regex} contains
7928 slashes. For example, it is more convenient to write @code{s,/,-,} than
7931 As in @command{sed}, you can give several replace expressions,
7932 separated by a semicolon.
7934 Supported @var{flags} are:
7938 Apply the replacement to @emph{all} matches to the @var{regexp}, not
7942 Use case-insensitive matching
7945 @var{regexp} is an @dfn{extended regular expression} (@pxref{Extended
7946 regexps, Extended regular expressions, Extended regular expressions,
7950 Only replace the @var{number}th match of the @var{regexp}.
7952 Note: the @acronym{POSIX} standard does not specify what should happen
7953 when you mix the @samp{g} and @var{number} modifiers. @GNUTAR{}
7954 follows the GNU @command{sed} implementation in this regard, so
7955 the interaction is defined to be: ignore matches before the
7956 @var{number}th, and then match and replace all matches from the
7961 In addition, several @dfn{transformation scope} flags are supported,
7962 that control to what files transformations apply. These are:
7966 Apply transformation to regular archive members.
7969 Do not apply transformation to regular archive members.
7972 Apply transformation to symbolic link targets.
7975 Do not apply transformation to symbolic link targets.
7978 Apply transformation to hard link targets.
7981 Do not apply transformation to hard link targets.
7984 Default is @samp{rsh}, which means to apply tranformations to both archive
7985 members and targets of symbolic and hard links.
7987 Default scope flags can also be changed using @samp{flags=} statement
7988 in the transform expression. The flags set this way remain in force
7989 until next @samp{flags=} statement or end of expression, whichever
7990 occurs first. For example:
7993 --transform 'flags=S;s|^|/usr/local/|'
7996 Here are several examples of @option{--transform} usage:
7999 @item Extract @file{usr/} hierarchy into @file{usr/local/}:
8002 $ @kbd{tar --transform='s,usr/,usr/local/,' -x -f arch.tar}
8005 @item Strip two leading directory components (equivalent to
8006 @option{--strip-components=2}):
8009 $ @kbd{tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar}
8012 @item Convert each file name to lower case:
8015 $ @kbd{tar --transform 's/.*/\L&/' -x -f arch.tar}
8018 @item Prepend @file{/prefix/} to each file name:
8021 $ @kbd{tar --transform 's,^,/prefix/,' -x -f arch.tar}
8024 @item Archive the @file{/lib} directory, prepending @samp{/usr/local}
8025 to each archive member:
8028 $ @kbd{tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib}
8032 Notice the use of flags in the last example. The @file{/lib}
8033 directory often contains many symbolic links to files within it.
8034 It may look, for example, like this:
8038 drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/
8039 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so
8040 lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so
8044 Using the expression @samp{s,^,/usr/local/,} would mean adding
8045 @samp{/usr/local} to both regular archive members and to link
8046 targets. In this case, @file{/lib/libc.so.6} would become:
8049 /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so
8052 This is definitely not desired. To avoid this, the @samp{S} flag
8053 are used, which excludes symbolic link targets from filename
8054 transformations. The result is:
8057 $ @kbd{tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \
8058 --show-transformed /lib}
8059 drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/
8060 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so
8061 lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 ->
8065 Unlike @option{--strip-components}, @option{--transform} can be used
8066 in any @GNUTAR{} operation mode. For example, the following command
8067 adds files to the archive while replacing the leading @file{usr/}
8068 component with @file{var/}:
8071 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' /}
8074 To test @option{--transform} effect we suggest using
8075 @option{--show-transformed-names} option:
8078 $ @kbd{tar -cf arch.tar --transform='s,^usr/,var/,' \
8079 --verbose --show-transformed-names /}
8082 If both @option{--strip-components} and @option{--transform} are used
8083 together, then @option{--transform} is applied first, and the required
8084 number of components is then stripped from its result.
8086 You can use as many @option{--transform} options in a single command
8087 line as you want. The specified expressions will then be applied in
8088 order of their appearance. For example, the following two invocations
8092 $ @kbd{tar -cf arch.tar --transform='s,/usr/var,/var/' \
8093 --transform='s,/usr/local,/usr/,'}
8094 $ @kbd{tar -cf arch.tar \
8095 --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'}
8099 @section Operating Only on New Files
8101 @cindex Excluding file by age
8102 @cindex Data Modification time, excluding files by
8103 @cindex Modification time, excluding files by
8104 @cindex Age, excluding files by
8105 The @option{--after-date=@var{date}} (@option{--newer=@var{date}},
8106 @option{-N @var{date}}) option causes @command{tar} to only work on
8107 files whose data modification or status change times are newer than
8108 the @var{date} given. If @var{date} starts with @samp{/} or @samp{.},
8109 it is taken to be a file name; the data modification time of that file
8110 is used as the date. If you use this option when creating or appending
8111 to an archive, the archive will only include new files. If you use
8112 @option{--after-date} when extracting an archive, @command{tar} will
8113 only extract files newer than the @var{date} you specify.
8115 If you only want @command{tar} to make the date comparison based on
8116 modification of the file's data (rather than status
8117 changes), then use the @option{--newer-mtime=@var{date}} option.
8119 @cindex --after-date and --update compared
8120 @cindex --newer-mtime and --update compared
8121 You may use these options with any operation. Note that these options
8122 differ from the @option{--update} (@option{-u}) operation in that they
8123 allow you to specify a particular date against which @command{tar} can
8124 compare when deciding whether or not to archive the files.
8129 @item --after-date=@var{date}
8130 @itemx --newer=@var{date}
8131 @itemx -N @var{date}
8132 Only store files newer than @var{date}.
8134 Acts on files only if their data modification or status change times are
8135 later than @var{date}. Use in conjunction with any operation.
8137 If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
8138 name; the data modification time of that file is used as the date.
8140 @opindex newer-mtime
8141 @item --newer-mtime=@var{date}
8142 Acts like @option{--after-date}, but only looks at data modification times.
8145 These options limit @command{tar} to operate only on files which have
8146 been modified after the date specified. A file's status is considered to have
8147 changed if its contents have been modified, or if its owner,
8148 permissions, and so forth, have been changed. (For more information on
8149 how to specify a date, see @ref{Date input formats}; remember that the
8150 entire date argument must be quoted if it contains any spaces.)
8152 Gurus would say that @option{--after-date} tests both the data
8153 modification time (@code{mtime}, the time the contents of the file
8154 were last modified) and the status change time (@code{ctime}, the time
8155 the file's status was last changed: owner, permissions, etc.@:)
8156 fields, while @option{--newer-mtime} tests only the @code{mtime}
8159 To be precise, @option{--after-date} checks @emph{both} @code{mtime} and
8160 @code{ctime} and processes the file if either one is more recent than
8161 @var{date}, while @option{--newer-mtime} only checks @code{mtime} and
8162 disregards @code{ctime}. Neither does it use @code{atime} (the last time the
8163 contents of the file were looked at).
8165 Date specifiers can have embedded spaces. Because of this, you may need
8166 to quote date arguments to keep the shell from parsing them as separate
8167 arguments. For example, the following command will add to the archive
8168 all the files modified less than two days ago:
8171 $ @kbd{tar -cf foo.tar --newer-mtime '2 days ago'}
8174 When any of these options is used with the option @option{--verbose}
8175 (@pxref{verbose tutorial}) @GNUTAR{} will try to convert the specified
8176 date back to its textual representation and compare that with the
8177 one given with the option. If the two dates differ, @command{tar} will
8178 print a warning saying what date it will use. This is to help user
8179 ensure he is using the right date. For example:
8183 $ @kbd{tar -c -f archive.tar --after-date='10 days ago' .}
8184 tar: Option --after-date: Treating date `10 days ago' as 2006-06-11
8190 @strong{Please Note:} @option{--after-date} and @option{--newer-mtime}
8191 should not be used for incremental backups. @xref{Incremental Dumps},
8192 for proper way of creating incremental backups.
8196 @section Descending into Directories
8197 @cindex Avoiding recursion in directories
8198 @cindex Descending directories, avoiding
8199 @cindex Directories, avoiding recursion
8200 @cindex Recursion in directories, avoiding
8202 Usually, @command{tar} will recursively explore all directories (either
8203 those given on the command line or through the @option{--files-from}
8204 option) for the various files they contain. However, you may not always
8205 want @command{tar} to act this way.
8207 @opindex no-recursion
8208 @cindex @command{find}, using with @command{tar}
8209 The @option{--no-recursion} option inhibits @command{tar}'s recursive descent
8210 into specified directories. If you specify @option{--no-recursion}, you can
8211 use the @command{find} (@pxref{Top,, find, find, GNU Find Manual})
8212 utility for hunting through levels of directories to
8213 construct a list of file names which you could then pass to @command{tar}.
8214 @command{find} allows you to be more selective when choosing which files to
8215 archive; see @ref{files}, for more information on using @command{find} with
8219 @item --no-recursion
8220 Prevents @command{tar} from recursively descending directories.
8224 Requires @command{tar} to recursively descend directories.
8225 This is the default.
8228 When you use @option{--no-recursion}, @GNUTAR{} grabs
8229 directory entries themselves, but does not descend on them
8230 recursively. Many people use @command{find} for locating files they
8231 want to back up, and since @command{tar} @emph{usually} recursively
8232 descends on directories, they have to use the @samp{@w{-not -type d}}
8233 test in their @command{find} invocation (@pxref{Type, Type, Type test,
8234 find, Finding Files}), as they usually do not want all the files in a
8235 directory. They then use the @option{--files-from} option to archive
8236 the files located via @command{find}.
8238 The problem when restoring files archived in this manner is that the
8239 directories themselves are not in the archive; so the
8240 @option{--same-permissions} (@option{--preserve-permissions},
8241 @option{-p}) option does not affect them---while users might really
8242 like it to. Specifying @option{--no-recursion} is a way to tell
8243 @command{tar} to grab only the directory entries given to it, adding
8244 no new files on its own. To summarize, if you use @command{find} to
8245 create a list of files to be stored in an archive, use it as follows:
8249 $ @kbd{find @var{dir} @var{tests} | \
8250 tar -cf @var{archive} -T - --no-recursion}
8254 The @option{--no-recursion} option also applies when extracting: it
8255 causes @command{tar} to extract only the matched directory entries, not
8256 the files under those directories.
8258 The @option{--no-recursion} option also affects how globbing patterns
8259 are interpreted (@pxref{controlling pattern-matching}).
8261 The @option{--no-recursion} and @option{--recursion} options apply to
8262 later options and operands, and can be overridden by later occurrences
8263 of @option{--no-recursion} and @option{--recursion}. For example:
8266 $ @kbd{tar -cf jams.tar --no-recursion grape --recursion grape/concord}
8270 creates an archive with one entry for @file{grape}, and the recursive
8271 contents of @file{grape/concord}, but no entries under @file{grape}
8272 other than @file{grape/concord}.
8275 @section Crossing File System Boundaries
8276 @cindex File system boundaries, not crossing
8278 @command{tar} will normally automatically cross file system boundaries in
8279 order to archive files which are part of a directory tree. You can
8280 change this behavior by running @command{tar} and specifying
8281 @option{--one-file-system}. This option only affects files that are
8282 archived because they are in a directory that is being archived;
8283 @command{tar} will still archive files explicitly named on the command line
8284 or through @option{--files-from}, regardless of where they reside.
8287 @opindex one-file-system
8288 @item --one-file-system
8289 Prevents @command{tar} from crossing file system boundaries when
8290 archiving. Use in conjunction with any write operation.
8293 The @option{--one-file-system} option causes @command{tar} to modify its
8294 normal behavior in archiving the contents of directories. If a file in
8295 a directory is not on the same file system as the directory itself, then
8296 @command{tar} will not archive that file. If the file is a directory
8297 itself, @command{tar} will not archive anything beneath it; in other words,
8298 @command{tar} will not cross mount points.
8300 This option is useful for making full or incremental archival backups of
8301 a file system. If this option is used in conjunction with
8302 @option{--verbose} (@option{-v}), files that are excluded are
8303 mentioned by name on the standard error.
8306 * directory:: Changing Directory
8307 * absolute:: Absolute File Names
8311 @subsection Changing the Working Directory
8313 @FIXME{need to read over this node now for continuity; i've switched
8314 things around some.}
8316 @cindex Changing directory mid-stream
8317 @cindex Directory, changing mid-stream
8318 @cindex Working directory, specifying
8319 To change the working directory in the middle of a list of file names,
8320 either on the command line or in a file specified using
8321 @option{--files-from} (@option{-T}), use @option{--directory} (@option{-C}).
8322 This will change the working directory to the specified directory
8323 after that point in the list.
8327 @item --directory=@var{directory}
8328 @itemx -C @var{directory}
8329 Changes the working directory in the middle of a command line.
8335 $ @kbd{tar -c -f jams.tar grape prune -C food cherry}
8339 will place the files @file{grape} and @file{prune} from the current
8340 directory into the archive @file{jams.tar}, followed by the file
8341 @file{cherry} from the directory @file{food}. This option is especially
8342 useful when you have several widely separated files that you want to
8343 store in the same archive.
8345 Note that the file @file{cherry} is recorded in the archive under the
8346 precise name @file{cherry}, @emph{not} @file{food/cherry}. Thus, the
8347 archive will contain three files that all appear to have come from the
8348 same directory; if the archive is extracted with plain @samp{tar
8349 --extract}, all three files will be written in the current directory.
8351 Contrast this with the command,
8354 $ @kbd{tar -c -f jams.tar grape prune -C food red/cherry}
8358 which records the third file in the archive under the name
8359 @file{red/cherry} so that, if the archive is extracted using
8360 @samp{tar --extract}, the third file will be written in a subdirectory
8361 named @file{orange-colored}.
8363 You can use the @option{--directory} option to make the archive
8364 independent of the original name of the directory holding the files.
8365 The following command places the files @file{/etc/passwd},
8366 @file{/etc/hosts}, and @file{/lib/libc.a} into the archive
8370 $ @kbd{tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a}
8374 However, the names of the archive members will be exactly what they were
8375 on the command line: @file{passwd}, @file{hosts}, and @file{libc.a}.
8376 They will not appear to be related by file name to the original
8377 directories where those files were located.
8379 Note that @option{--directory} options are interpreted consecutively. If
8380 @option{--directory} specifies a relative file name, it is interpreted
8381 relative to the then current directory, which might not be the same as
8382 the original current working directory of @command{tar}, due to a previous
8383 @option{--directory} option.
8385 When using @option{--files-from} (@pxref{files}), you can put various
8386 @command{tar} options (including @option{-C}) in the file list. Notice,
8387 however, that in this case the option and its argument may not be
8388 separated by whitespace. If you use short option, its argument must
8389 either follow the option letter immediately, without any intervening
8390 whitespace, or occupy the next line. Otherwise, if you use long
8391 option, separate its argument by an equal sign.
8393 For instance, the file list for the above example will be:
8406 To use it, you would invoke @command{tar} as follows:
8409 $ @kbd{tar -c -f foo.tar --files-from list}
8412 The interpretation of @option{--directory} is disabled by
8413 @option{--null} option.
8416 @subsection Absolute File Names
8417 @cindex absolute file names
8418 @cindex file names, absolute
8420 By default, @GNUTAR{} drops a leading @samp{/} on
8421 input or output, and complains about file names containing a @file{..}
8422 component. There is an option that turns off this behavior:
8425 @opindex absolute-names
8426 @item --absolute-names
8428 Do not strip leading slashes from file names, and permit file names
8429 containing a @file{..} file name component.
8432 When @command{tar} extracts archive members from an archive, it strips any
8433 leading slashes (@samp{/}) from the member name. This causes absolute
8434 member names in the archive to be treated as relative file names. This
8435 allows you to have such members extracted wherever you want, instead of
8436 being restricted to extracting the member in the exact directory named
8437 in the archive. For example, if the archive member has the name
8438 @file{/etc/passwd}, @command{tar} will extract it as if the name were
8439 really @file{etc/passwd}.
8441 File names containing @file{..} can cause problems when extracting, so
8442 @command{tar} normally warns you about such files when creating an
8443 archive, and rejects attempts to extracts such files.
8445 Other @command{tar} programs do not do this. As a result, if you
8446 create an archive whose member names start with a slash, they will be
8447 difficult for other people with a non-@GNUTAR{}
8448 program to use. Therefore, @GNUTAR{} also strips
8449 leading slashes from member names when putting members into the
8450 archive. For example, if you ask @command{tar} to add the file
8451 @file{/bin/ls} to an archive, it will do so, but the member name will
8452 be @file{bin/ls}.@footnote{A side effect of this is that when
8453 @option{--create} is used with @option{--verbose} the resulting output
8454 is not, generally speaking, the same as the one you'd get running
8455 @kbd{tar --list} command. This may be important if you use some
8456 scripts for comparing both outputs. @xref{listing member and file names},
8457 for the information on how to handle this case.}
8459 If you use the @option{--absolute-names} (@option{-P}) option,
8460 @command{tar} will do none of these transformations.
8462 To archive or extract files relative to the root directory, specify
8463 the @option{--absolute-names} (@option{-P}) option.
8465 Normally, @command{tar} acts on files relative to the working
8466 directory---ignoring superior directory names when archiving, and
8467 ignoring leading slashes when extracting.
8469 When you specify @option{--absolute-names} (@option{-P}),
8470 @command{tar} stores file names including all superior directory
8471 names, and preserves leading slashes. If you only invoked
8472 @command{tar} from the root directory you would never need the
8473 @option{--absolute-names} option, but using this option
8474 may be more convenient than switching to root.
8476 @FIXME{Should be an example in the tutorial/wizardry section using this
8477 to transfer files between systems.}
8480 @item --absolute-names
8481 Preserves full file names (including superior directory names) when
8482 archiving files. Preserves leading slash when extracting files.
8486 @command{tar} prints out a message about removing the @samp{/} from
8487 file names. This message appears once per @GNUTAR{}
8488 invocation. It represents something which ought to be told; ignoring
8489 what it means can cause very serious surprises, later.
8491 Some people, nevertheless, do not want to see this message. Wanting to
8492 play really dangerously, one may of course redirect @command{tar} standard
8493 error to the sink. For example, under @command{sh}:
8496 $ @kbd{tar -c -f archive.tar /home 2> /dev/null}
8500 Another solution, both nicer and simpler, would be to change to
8501 the @file{/} directory first, and then avoid absolute notation.
8505 $ @kbd{tar -c -f archive.tar -C / home}
8508 @include getdate.texi
8511 @chapter Controlling the Archive Format
8513 @cindex Tar archive formats
8514 Due to historical reasons, there are several formats of tar archives.
8515 All of them are based on the same principles, but have some subtle
8516 differences that often make them incompatible with each other.
8518 GNU tar is able to create and handle archives in a variety of formats.
8519 The most frequently used formats are (in alphabetical order):
8523 Format used by @GNUTAR{} versions up to 1.13.25. This format derived
8524 from an early @acronym{POSIX} standard, adding some improvements such as
8525 sparse file handling and incremental archives. Unfortunately these
8526 features were implemented in a way incompatible with other archive
8529 Archives in @samp{gnu} format are able to hold file names of unlimited
8533 Format used by @GNUTAR{} of versions prior to 1.12.
8536 Archive format, compatible with the V7 implementation of tar. This
8537 format imposes a number of limitations. The most important of them
8541 @item The maximum length of a file name is limited to 99 characters.
8542 @item The maximum length of a symbolic link is limited to 99 characters.
8543 @item It is impossible to store special files (block and character
8544 devices, fifos etc.)
8545 @item Maximum value of user or group @acronym{ID} is limited to 2097151 (7777777
8547 @item V7 archives do not contain symbolic ownership information (user
8548 and group name of the file owner).
8551 This format has traditionally been used by Automake when producing
8552 Makefiles. This practice will change in the future, in the meantime,
8553 however this means that projects containing file names more than 99
8554 characters long will not be able to use @GNUTAR{} @value{VERSION} and
8555 Automake prior to 1.9.
8558 Archive format defined by @acronym{POSIX.1-1988} specification. It stores
8559 symbolic ownership information. It is also able to store
8560 special files. However, it imposes several restrictions as well:
8563 @item The maximum length of a file name is limited to 256 characters,
8564 provided that the file name can be split at a directory separator in
8565 two parts, first of them being at most 155 bytes long. So, in most
8566 cases the maximum file name length will be shorter than 256
8568 @item The maximum length of a symbolic link name is limited to
8570 @item Maximum size of a file the archive is able to accommodate
8572 @item Maximum value of UID/GID is 2097151.
8573 @item Maximum number of bits in device major and minor numbers is 21.
8577 Format used by J@"org Schilling @command{star}
8578 implementation. @GNUTAR{} is able to read @samp{star} archives but
8579 currently does not produce them.
8582 Archive format defined by @acronym{POSIX.1-2001} specification. This is the
8583 most flexible and feature-rich format. It does not impose any
8584 restrictions on file sizes or file name lengths. This format is quite
8585 recent, so not all tar implementations are able to handle it properly.
8586 However, this format is designed in such a way that any tar
8587 implementation able to read @samp{ustar} archives will be able to read
8588 most @samp{posix} archives as well, with the only exception that any
8589 additional information (such as long file names etc.) will in such
8590 case be extracted as plain text files along with the files it refers to.
8592 This archive format will be the default format for future versions
8597 The following table summarizes the limitations of each of these
8600 @multitable @columnfractions .10 .20 .20 .20 .20
8601 @headitem Format @tab UID @tab File Size @tab File Name @tab Devn
8602 @item gnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8603 @item oldgnu @tab 1.8e19 @tab Unlimited @tab Unlimited @tab 63
8604 @item v7 @tab 2097151 @tab 8GB @tab 99 @tab n/a
8605 @item ustar @tab 2097151 @tab 8GB @tab 256 @tab 21
8606 @item posix @tab Unlimited @tab Unlimited @tab Unlimited @tab Unlimited
8609 The default format for @GNUTAR{} is defined at compilation
8610 time. You may check it by running @command{tar --help}, and examining
8611 the last lines of its output. Usually, @GNUTAR{} is configured
8612 to create archives in @samp{gnu} format, however, future version will
8613 switch to @samp{posix}.
8616 * Compression:: Using Less Space through Compression
8617 * Attributes:: Handling File Attributes
8618 * Portability:: Making @command{tar} Archives More Portable
8619 * cpio:: Comparison of @command{tar} and @command{cpio}
8623 @section Using Less Space through Compression
8626 * gzip:: Creating and Reading Compressed Archives
8627 * sparse:: Archiving Sparse Files
8631 @subsection Creating and Reading Compressed Archives
8632 @cindex Compressed archives
8633 @cindex Storing archives in compressed format
8641 @GNUTAR{} is able to create and read compressed archives. It supports
8642 @command{gzip}, @command{bzip2}, @command{lzip}, @command{lzma} and
8643 @command{lzop} compression programs. For backward compatibility, it
8644 also supports @command{compress} command, although we strongly recommend
8645 against using it, because it is by far less effective than other
8646 compression programs@footnote{It also had patent problems in the past.}.
8648 Creating a compressed archive is simple: you just specify a
8649 @dfn{compression option} along with the usual archive creation
8650 commands. The compression option is @option{-z} (@option{--gzip}) to
8651 create a @command{gzip} compressed archive, @option{-j}
8652 (@option{--bzip2}) to create a @command{bzip2} compressed archive,
8653 @option{--lzip} to create an @asis{lzip} compressed archive,
8654 @option{-J} (@option{--xz}) to create an @asis{XZ} archive,
8655 @option{--lzma} to create an @asis{LZMA} compressed
8656 archive, @option{--lzop} to create an @asis{LSOP} archive, and
8657 @option{-Z} (@option{--compress}) to use @command{compress} program.
8661 $ @kbd{tar cfz archive.tar.gz .}
8664 You can also let @GNUTAR{} select the compression program basing on
8665 the suffix of the archive file name. This is done using
8666 @option{--auto-compress} (@option{-a}) command line option. For
8667 example, the following invocation will use @command{bzip2} for
8671 $ @kbd{tar cfa archive.tar.bz2 .}
8675 whereas the following one will use @command{lzma}:
8678 $ @kbd{tar cfa archive.tar.lzma .}
8681 For a complete list of file name suffixes recognized by @GNUTAR{},
8682 @ref{auto-compress}.
8684 Reading compressed archive is even simpler: you don't need to specify
8685 any additional options as @GNUTAR{} recognizes its format
8686 automatically. Thus, the following commands will list and extract the
8687 archive created in previous example:
8690 # List the compressed archive
8691 $ @kbd{tar tf archive.tar.gz}
8692 # Extract the compressed archive
8693 $ @kbd{tar xf archive.tar.gz}
8696 The format recognition algorithm is based on @dfn{signatures}, a
8697 special byte sequences in the beginning of file, that are specific for
8698 certain compression formats. If this approach fails, @command{tar}
8699 falls back to using archive name suffix to determine its format
8700 (@xref{auto-compress}, for a list of recognized suffixes).
8702 The only case when you have to specify a decompression option while
8703 reading the archive is when reading from a pipe or from a tape drive
8704 that does not support random access. However, in this case @GNUTAR{}
8705 will indicate which option you should use. For example:
8708 $ @kbd{cat archive.tar.gz | tar tf -}
8709 tar: Archive is compressed. Use -z option
8710 tar: Error is not recoverable: exiting now
8713 If you see such diagnostics, just add the suggested option to the
8714 invocation of @GNUTAR{}:
8717 $ @kbd{cat archive.tar.gz | tar tfz -}
8720 Notice also, that there are several restrictions on operations on
8721 compressed archives. First of all, compressed archives cannot be
8722 modified, i.e., you cannot update (@option{--update} (@option{-u}))
8723 them or delete (@option{--delete}) members from them or
8724 add (@option{--append} (@option{-r})) members to them. Likewise, you
8725 cannot append another @command{tar} archive to a compressed archive using
8726 @option{--concatenate} (@option{-A})). Secondly, multi-volume
8727 archives cannot be compressed.
8729 The following table summarizes compression options used by @GNUTAR{}.
8732 @anchor{auto-compress}
8733 @opindex auto-compress
8734 @item --auto-compress
8736 Select a compression program to use by the archive file name
8737 suffix. The following suffixes are recognized:
8739 @multitable @columnfractions 0.3 0.6
8740 @headitem Suffix @tab Compression program
8741 @item @samp{.gz} @tab @command{gzip}
8742 @item @samp{.tgz} @tab @command{gzip}
8743 @item @samp{.taz} @tab @command{gzip}
8744 @item @samp{.Z} @tab @command{compress}
8745 @item @samp{.taZ} @tab @command{compress}
8746 @item @samp{.bz2} @tab @command{bzip2}
8747 @item @samp{.tz2} @tab @command{bzip2}
8748 @item @samp{.tbz2} @tab @command{bzip2}
8749 @item @samp{.tbz} @tab @command{bzip2}
8750 @item @samp{.lz} @tab @command{lzip}
8751 @item @samp{.lzma} @tab @command{lzma}
8752 @item @samp{.tlz} @tab @command{lzma}
8753 @item @samp{.lzo} @tab @command{lzop}
8754 @item @samp{.xz} @tab @command{xz}
8762 Filter the archive through @command{gzip}.
8764 You can use @option{--gzip} and @option{--gunzip} on physical devices
8765 (tape drives, etc.) and remote files as well as on normal files; data
8766 to or from such devices or remote files is reblocked by another copy
8767 of the @command{tar} program to enforce the specified (or default) record
8768 size. The default compression parameters are used; if you need to
8769 override them, set @env{GZIP} environment variable, e.g.:
8772 $ @kbd{GZIP=--best tar cfz archive.tar.gz subdir}
8776 Another way would be to avoid the @option{--gzip} (@option{--gunzip}, @option{--ungzip}, @option{-z}) option and run
8777 @command{gzip} explicitly:
8780 $ @kbd{tar cf - subdir | gzip --best -c - > archive.tar.gz}
8783 @cindex corrupted archives
8784 About corrupted compressed archives: @command{gzip}'ed files have no
8785 redundancy, for maximum compression. The adaptive nature of the
8786 compression scheme means that the compression tables are implicitly
8787 spread all over the archive. If you lose a few blocks, the dynamic
8788 construction of the compression tables becomes unsynchronized, and there
8789 is little chance that you could recover later in the archive.
8791 There are pending suggestions for having a per-volume or per-file
8792 compression in @GNUTAR{}. This would allow for viewing the
8793 contents without decompression, and for resynchronizing decompression at
8794 every volume or file, in case of corrupted archives. Doing so, we might
8795 lose some compressibility. But this would have make recovering easier.
8796 So, there are pros and cons. We'll see!
8801 Filter the archive through @code{xz}. Otherwise like
8806 Filter the archive through @code{bzip2}. Otherwise like @option{--gzip}.
8810 Filter the archive through @command{lzip}. Otherwise like @option{--gzip}.
8814 Filter the archive through @command{lzma}. Otherwise like @option{--gzip}.
8818 Filter the archive through @command{lzop}. Otherwise like
8826 Filter the archive through @command{compress}. Otherwise like @option{--gzip}.
8828 @opindex use-compress-program
8829 @item --use-compress-program=@var{prog}
8830 @itemx -I=@var{prog}
8831 Use external compression program @var{prog}. Use this option if you
8832 have a compression program that @GNUTAR{} does not support. There
8833 are two requirements to which @var{prog} should comply:
8835 First, when called without options, it should read data from standard
8836 input, compress it and output it on standard output.
8838 Secondly, if called with @option{-d} argument, it should do exactly
8839 the opposite, i.e., read the compressed data from the standard input
8840 and produce uncompressed data on the standard output.
8843 @cindex gpg, using with tar
8844 @cindex gnupg, using with tar
8845 @cindex Using encrypted archives
8846 The @option{--use-compress-program} option, in particular, lets you
8847 implement your own filters, not necessarily dealing with
8848 compression/decompression. For example, suppose you wish to implement
8849 PGP encryption on top of compression, using @command{gpg} (@pxref{Top,
8850 gpg, gpg ---- encryption and signing tool, gpg, GNU Privacy Guard
8851 Manual}). The following script does that:
8857 -d) gpg --decrypt - | gzip -d -c;;
8858 '') gzip -c | gpg -s ;;
8859 *) echo "Unknown option $1">&2; exit 1;;
8864 Suppose you name it @file{gpgz} and save it somewhere in your
8865 @env{PATH}. Then the following command will create a compressed
8866 archive signed with your private key:
8869 $ @kbd{tar -cf foo.tar.gpgz -Igpgz .}
8873 Likewise, the command below will list its contents:
8876 $ @kbd{tar -tf foo.tar.gpgz -Igpgz .}
8880 The above is based on the following discussion:
8882 I have one question, or maybe it's a suggestion if there isn't a way
8883 to do it now. I would like to use @option{--gzip}, but I'd also like
8884 the output to be fed through a program like @acronym{GNU}
8885 @command{ecc} (actually, right now that's @samp{exactly} what I'd like
8886 to use :-)), basically adding ECC protection on top of compression.
8887 It seems as if this should be quite easy to do, but I can't work out
8888 exactly how to go about it. Of course, I can pipe the standard output
8889 of @command{tar} through @command{ecc}, but then I lose (though I
8890 haven't started using it yet, I confess) the ability to have
8891 @command{tar} use @command{rmt} for it's I/O (I think).
8893 I think the most straightforward thing would be to let me specify a
8894 general set of filters outboard of compression (preferably ordered,
8895 so the order can be automatically reversed on input operations, and
8896 with the options they require specifiable), but beggars shouldn't be
8897 choosers and anything you decide on would be fine with me.
8899 By the way, I like @command{ecc} but if (as the comments say) it can't
8900 deal with loss of block sync, I'm tempted to throw some time at adding
8901 that capability. Supposing I were to actually do such a thing and
8902 get it (apparently) working, do you accept contributed changes to
8903 utilities like that? (Leigh Clayton @file{loc@@soliton.com}, May 1995).
8905 Isn't that exactly the role of the
8906 @option{--use-compress-prog=@var{program}} option?
8907 I never tried it myself, but I suspect you may want to write a
8908 @var{prog} script or program able to filter stdin to stdout to
8909 way you want. It should recognize the @option{-d} option, for when
8910 extraction is needed rather than creation.
8912 It has been reported that if one writes compressed data (through the
8913 @option{--gzip} or @option{--compress} options) to a DLT and tries to use
8914 the DLT compression mode, the data will actually get bigger and one will
8915 end up with less space on the tape.
8919 @subsection Archiving Sparse Files
8920 @cindex Sparse Files
8922 Files in the file system occasionally have @dfn{holes}. A @dfn{hole}
8923 in a file is a section of the file's contents which was never written.
8924 The contents of a hole reads as all zeros. On many operating systems,
8925 actual disk storage is not allocated for holes, but they are counted
8926 in the length of the file. If you archive such a file, @command{tar}
8927 could create an archive longer than the original. To have @command{tar}
8928 attempt to recognize the holes in a file, use @option{--sparse}
8929 (@option{-S}). When you use this option, then, for any file using
8930 less disk space than would be expected from its length, @command{tar}
8931 searches the file for consecutive stretches of zeros. It then records
8932 in the archive for the file where the consecutive stretches of zeros
8933 are, and only archives the ``real contents'' of the file. On
8934 extraction (using @option{--sparse} is not needed on extraction) any
8935 such files have holes created wherever the continuous stretches of zeros
8936 were found. Thus, if you use @option{--sparse}, @command{tar} archives
8937 won't take more space than the original.
8943 This option instructs @command{tar} to test each file for sparseness
8944 before attempting to archive it. If the file is found to be sparse it
8945 is treated specially, thus allowing to decrease the amount of space
8946 used by its image in the archive.
8948 This option is meaningful only when creating or updating archives. It
8949 has no effect on extraction.
8952 Consider using @option{--sparse} when performing file system backups,
8953 to avoid archiving the expanded forms of files stored sparsely in the
8956 Even if your system has no sparse files currently, some may be
8957 created in the future. If you use @option{--sparse} while making file
8958 system backups as a matter of course, you can be assured the archive
8959 will never take more space on the media than the files take on disk
8960 (otherwise, archiving a disk filled with sparse files might take
8961 hundreds of tapes). @xref{Incremental Dumps}.
8963 However, be aware that @option{--sparse} option presents a serious
8964 drawback. Namely, in order to determine if the file is sparse
8965 @command{tar} has to read it before trying to archive it, so in total
8966 the file is read @strong{twice}. So, always bear in mind that the
8967 time needed to process all files with this option is roughly twice
8968 the time needed to archive them without it.
8969 @FIXME{A technical note:
8971 Programs like @command{dump} do not have to read the entire file; by
8972 examining the file system directly, they can determine in advance
8973 exactly where the holes are and thus avoid reading through them. The
8974 only data it need read are the actual allocated data blocks.
8975 @GNUTAR{} uses a more portable and straightforward
8976 archiving approach, it would be fairly difficult that it does
8977 otherwise. Elizabeth Zwicky writes to @file{comp.unix.internals}, on
8981 What I did say is that you cannot tell the difference between a hole and an
8982 equivalent number of nulls without reading raw blocks. @code{st_blocks} at
8983 best tells you how many holes there are; it doesn't tell you @emph{where}.
8984 Just as programs may, conceivably, care what @code{st_blocks} is (care
8985 to name one that does?), they may also care where the holes are (I have
8986 no examples of this one either, but it's equally imaginable).
8988 I conclude from this that good archivers are not portable. One can
8989 arguably conclude that if you want a portable program, you can in good
8990 conscience restore files with as many holes as possible, since you can't
8995 @cindex sparse formats, defined
8996 When using @samp{POSIX} archive format, @GNUTAR{} is able to store
8997 sparse files using in three distinct ways, called @dfn{sparse
8998 formats}. A sparse format is identified by its @dfn{number},
8999 consisting, as usual of two decimal numbers, delimited by a dot. By
9000 default, format @samp{1.0} is used. If, for some reason, you wish to
9001 use an earlier format, you can select it using
9002 @option{--sparse-version} option.
9005 @opindex sparse-version
9006 @item --sparse-version=@var{version}
9008 Select the format to store sparse files in. Valid @var{version} values
9009 are: @samp{0.0}, @samp{0.1} and @samp{1.0}. @xref{Sparse Formats},
9010 for a detailed description of each format.
9013 Using @option{--sparse-format} option implies @option{--sparse}.
9016 @section Handling File Attributes
9017 @cindex atrributes, files
9018 @cindex file attributes
9020 When @command{tar} reads files, it updates their access times. To
9021 avoid this, use the @option{--atime-preserve[=METHOD]} option, which can either
9022 reset the access time retroactively or avoid changing it in the first
9026 @opindex atime-preserve
9027 @item --atime-preserve
9028 @itemx --atime-preserve=replace
9029 @itemx --atime-preserve=system
9030 Preserve the access times of files that are read. This works only for
9031 files that you own, unless you have superuser privileges.
9033 @option{--atime-preserve=replace} works on most systems, but it also
9034 restores the data modification time and updates the status change
9035 time. Hence it doesn't interact with incremental dumps nicely
9036 (@pxref{Incremental Dumps}), and it can set access or data modification times
9037 incorrectly if other programs access the file while @command{tar} is
9040 @option{--atime-preserve=system} avoids changing the access time in
9041 the first place, if the operating system supports this.
9042 Unfortunately, this may or may not work on any given operating system
9043 or file system. If @command{tar} knows for sure it won't work, it
9044 complains right away.
9046 Currently @option{--atime-preserve} with no operand defaults to
9047 @option{--atime-preserve=replace}, but this is intended to change to
9048 @option{--atime-preserve=system} when the latter is better-supported.
9053 Do not extract data modification time.
9055 When this option is used, @command{tar} leaves the data modification times
9056 of the files it extracts as the times when the files were extracted,
9057 instead of setting it to the times recorded in the archive.
9059 This option is meaningless with @option{--list} (@option{-t}).
9063 Create extracted files with the same ownership they have in the
9066 This is the default behavior for the superuser,
9067 so this option is meaningful only for non-root users, when @command{tar}
9068 is executed on those systems able to give files away. This is
9069 considered as a security flaw by many people, at least because it
9070 makes quite difficult to correctly account users for the disk space
9071 they occupy. Also, the @code{suid} or @code{sgid} attributes of
9072 files are easily and silently lost when files are given away.
9074 When writing an archive, @command{tar} writes the user @acronym{ID} and user name
9075 separately. If it can't find a user name (because the user @acronym{ID} is not
9076 in @file{/etc/passwd}), then it does not write one. When restoring,
9077 it tries to look the name (if one was written) up in
9078 @file{/etc/passwd}. If it fails, then it uses the user @acronym{ID} stored in
9079 the archive instead.
9081 @opindex no-same-owner
9082 @item --no-same-owner
9084 Do not attempt to restore ownership when extracting. This is the
9085 default behavior for ordinary users, so this option has an effect
9086 only for the superuser.
9088 @opindex numeric-owner
9089 @item --numeric-owner
9090 The @option{--numeric-owner} option allows (ANSI) archives to be written
9091 without user/group name information or such information to be ignored
9092 when extracting. It effectively disables the generation and/or use
9093 of user/group name information. This option forces extraction using
9094 the numeric ids from the archive, ignoring the names.
9096 This is useful in certain circumstances, when restoring a backup from
9097 an emergency floppy with different passwd/group files for example.
9098 It is otherwise impossible to extract files with the right ownerships
9099 if the password file in use during the extraction does not match the
9100 one belonging to the file system(s) being extracted. This occurs,
9101 for example, if you are restoring your files after a major crash and
9102 had booted from an emergency floppy with no password file or put your
9103 disk into another machine to do the restore.
9105 The numeric ids are @emph{always} saved into @command{tar} archives.
9106 The identifying names are added at create time when provided by the
9107 system, unless @option{--old-archive} (@option{-o}) is used. Numeric ids could be
9108 used when moving archives between a collection of machines using
9109 a centralized management for attribution of numeric ids to users
9110 and groups. This is often made through using the NIS capabilities.
9112 When making a @command{tar} file for distribution to other sites, it
9113 is sometimes cleaner to use a single owner for all files in the
9114 distribution, and nicer to specify the write permission bits of the
9115 files as stored in the archive independently of their actual value on
9116 the file system. The way to prepare a clean distribution is usually
9117 to have some Makefile rule creating a directory, copying all needed
9118 files in that directory, then setting ownership and permissions as
9119 wanted (there are a lot of possible schemes), and only then making a
9120 @command{tar} archive out of this directory, before cleaning
9121 everything out. Of course, we could add a lot of options to
9122 @GNUTAR{} for fine tuning permissions and ownership.
9123 This is not the good way, I think. @GNUTAR{} is
9124 already crowded with options and moreover, the approach just explained
9125 gives you a great deal of control already.
9127 @xopindex{same-permissions, short description}
9128 @xopindex{preserve-permissions, short description}
9130 @itemx --same-permissions
9131 @itemx --preserve-permissions
9132 Extract all protection information.
9134 This option causes @command{tar} to set the modes (access permissions) of
9135 extracted files exactly as recorded in the archive. If this option
9136 is not used, the current @code{umask} setting limits the permissions
9137 on extracted files. This option is by default enabled when
9138 @command{tar} is executed by a superuser.
9141 This option is meaningless with @option{--list} (@option{-t}).
9145 Same as both @option{--same-permissions} and @option{--same-order}.
9147 This option is deprecated, and will be removed in @GNUTAR{} version 1.23.
9152 @section Making @command{tar} Archives More Portable
9154 Creating a @command{tar} archive on a particular system that is meant to be
9155 useful later on many other machines and with other versions of @command{tar}
9156 is more challenging than you might think. @command{tar} archive formats
9157 have been evolving since the first versions of Unix. Many such formats
9158 are around, and are not always compatible with each other. This section
9159 discusses a few problems, and gives some advice about making @command{tar}
9160 archives more portable.
9162 One golden rule is simplicity. For example, limit your @command{tar}
9163 archives to contain only regular files and directories, avoiding
9164 other kind of special files. Do not attempt to save sparse files or
9165 contiguous files as such. Let's discuss a few more problems, in turn.
9167 @FIXME{Discuss GNU extensions (incremental backups, multi-volume
9168 archives and archive labels) in GNU and PAX formats.}
9171 * Portable Names:: Portable Names
9172 * dereference:: Symbolic Links
9173 * hard links:: Hard Links
9174 * old:: Old V7 Archives
9175 * ustar:: Ustar Archives
9176 * gnu:: GNU and old GNU format archives.
9177 * posix:: @acronym{POSIX} archives
9178 * Checksumming:: Checksumming Problems
9179 * Large or Negative Values:: Large files, negative time stamps, etc.
9180 * Other Tars:: How to Extract GNU-Specific Data Using
9181 Other @command{tar} Implementations
9184 @node Portable Names
9185 @subsection Portable Names
9187 Use portable file and member names. A name is portable if it contains
9188 only @acronym{ASCII} letters and digits, @samp{/}, @samp{.}, @samp{_}, and
9189 @samp{-}; it cannot be empty, start with @samp{-} or @samp{//}, or
9190 contain @samp{/-}. Avoid deep directory nesting. For portability to
9191 old Unix hosts, limit your file name components to 14 characters or
9194 If you intend to have your @command{tar} archives to be read under
9195 MSDOS, you should not rely on case distinction for file names, and you
9196 might use the @acronym{GNU} @command{doschk} program for helping you
9197 further diagnosing illegal MSDOS names, which are even more limited
9201 @subsection Symbolic Links
9202 @cindex File names, using symbolic links
9203 @cindex Symbolic link as file name
9205 @opindex dereference
9206 Normally, when @command{tar} archives a symbolic link, it writes a
9207 block to the archive naming the target of the link. In that way, the
9208 @command{tar} archive is a faithful record of the file system contents.
9209 @option{--dereference} (@option{-h}) is used with @option{--create} (@option{-c}), and causes
9210 @command{tar} to archive the files symbolic links point to, instead of
9211 the links themselves. When this option is used, when @command{tar}
9212 encounters a symbolic link, it will archive the linked-to file,
9213 instead of simply recording the presence of a symbolic link.
9215 The name under which the file is stored in the file system is not
9216 recorded in the archive. To record both the symbolic link name and
9217 the file name in the system, archive the file under both names. If
9218 all links were recorded automatically by @command{tar}, an extracted file
9219 might be linked to a file name that no longer exists in the file
9222 If a linked-to file is encountered again by @command{tar} while creating
9223 the same archive, an entire second copy of it will be stored. (This
9224 @emph{might} be considered a bug.)
9226 So, for portable archives, do not archive symbolic links as such,
9227 and use @option{--dereference} (@option{-h}): many systems do not support
9228 symbolic links, and moreover, your distribution might be unusable if
9229 it contains unresolved symbolic links.
9232 @subsection Hard Links
9233 @cindex File names, using hard links
9234 @cindex hard links, dereferencing
9235 @cindex dereferencing hard links
9237 Normally, when @command{tar} archives a hard link, it writes a
9238 block to the archive naming the target of the link (a @samp{1} type
9239 block). In that way, the actual file contents is stored in file only
9240 once. For example, consider the following two files:
9245 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 one
9246 -rw-r--r-- 2 gray staff 4 2007-10-30 15:11 jeden
9250 Here, @file{jeden} is a link to @file{one}. When archiving this
9251 directory with a verbose level 2, you will get an output similar to
9255 $ tar cfvv ../archive.tar .
9256 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9257 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9258 hrw-r--r-- gray/staff 0 2007-10-30 15:11 ./one link to ./jeden
9261 The last line shows that, instead of storing two copies of the file,
9262 @command{tar} stored it only once, under the name @file{jeden}, and
9263 stored file @file{one} as a hard link to this file.
9265 It may be important to know that all hard links to the given file are
9266 stored in the archive. For example, this may be necessary for exact
9267 reproduction of the file system. The following option does that:
9270 @xopindex{check-links, described}
9273 Check the number of links dumped for each processed file. If this
9274 number does not match the total number of hard links for the file, print
9278 For example, trying to archive only file @file{jeden} with this option
9279 produces the following diagnostics:
9282 $ tar -c -f ../archive.tar jeden
9283 tar: Missing links to `jeden'.
9286 Although creating special records for hard links helps keep a faithful
9287 record of the file system contents and makes archives more compact, it
9288 may present some difficulties when extracting individual members from
9289 the archive. For example, trying to extract file @file{one} from the
9290 archive created in previous examples produces, in the absense of file
9294 $ tar xf archive.tar ./one
9295 tar: ./one: Cannot hard link to `./jeden': No such file or directory
9296 tar: Error exit delayed from previous errors
9299 The reason for this behavior is that @command{tar} cannot seek back in
9300 the archive to the previous member (in this case, @file{one}), to
9301 extract it@footnote{There are plans to fix this in future releases.}.
9302 If you wish to avoid such problems at the cost of a bigger archive,
9303 use the following option:
9306 @xopindex{hard-dereference, described}
9307 @item --hard-dereference
9308 Dereference hard links and store the files they refer to.
9311 For example, trying this option on our two sample files, we get two
9312 copies in the archive, each of which can then be extracted
9313 independently of the other:
9317 $ tar -c -vv -f ../archive.tar --hard-dereference .
9318 drwxr-xr-x gray/staff 0 2007-10-30 15:13 ./
9319 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./jeden
9320 -rw-r--r-- gray/staff 4 2007-10-30 15:11 ./one
9325 @subsection Old V7 Archives
9326 @cindex Format, old style
9327 @cindex Old style format
9328 @cindex Old style archives
9329 @cindex v7 archive format
9331 Certain old versions of @command{tar} cannot handle additional
9332 information recorded by newer @command{tar} programs. To create an
9333 archive in V7 format (not ANSI), which can be read by these old
9334 versions, specify the @option{--format=v7} option in
9335 conjunction with the @option{--create} (@option{-c}) (@command{tar} also
9336 accepts @option{--portability} or @option{--old-archive} for this
9337 option). When you specify it,
9338 @command{tar} leaves out information about directories, pipes, fifos,
9339 contiguous files, and device files, and specifies file ownership by
9340 group and user IDs instead of group and user names.
9342 When updating an archive, do not use @option{--format=v7}
9343 unless the archive was created using this option.
9345 In most cases, a @emph{new} format archive can be read by an @emph{old}
9346 @command{tar} program without serious trouble, so this option should
9347 seldom be needed. On the other hand, most modern @command{tar}s are
9348 able to read old format archives, so it might be safer for you to
9349 always use @option{--format=v7} for your distributions. Notice,
9350 however, that @samp{ustar} format is a better alternative, as it is
9351 free from many of @samp{v7}'s drawbacks.
9354 @subsection Ustar Archive Format
9356 @cindex ustar archive format
9357 Archive format defined by @acronym{POSIX}.1-1988 specification is called
9358 @code{ustar}. Although it is more flexible than the V7 format, it
9359 still has many restrictions (@xref{Formats,ustar}, for the detailed
9360 description of @code{ustar} format). Along with V7 format,
9361 @code{ustar} format is a good choice for archives intended to be read
9362 with other implementations of @command{tar}.
9364 To create archive in @code{ustar} format, use @option{--format=ustar}
9365 option in conjunction with the @option{--create} (@option{-c}).
9368 @subsection @acronym{GNU} and old @GNUTAR{} format
9370 @cindex GNU archive format
9371 @cindex Old GNU archive format
9372 @GNUTAR{} was based on an early draft of the
9373 @acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
9374 @command{tar}, such as the support for file names longer than 100
9375 characters, use portions of the @command{tar} header record which were
9376 specified in that @acronym{POSIX} draft as unused. Subsequent changes in
9377 @acronym{POSIX} have allocated the same parts of the header record for
9378 other purposes. As a result, @GNUTAR{} format is
9379 incompatible with the current @acronym{POSIX} specification, and with
9380 @command{tar} programs that follow it.
9382 In the majority of cases, @command{tar} will be configured to create
9383 this format by default. This will change in future releases, since
9384 we plan to make @samp{POSIX} format the default.
9386 To force creation a @GNUTAR{} archive, use option
9387 @option{--format=gnu}.
9390 @subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
9392 @cindex POSIX archive format
9393 @cindex PAX archive format
9394 Starting from version 1.14 @GNUTAR{} features full support for
9395 @acronym{POSIX.1-2001} archives.
9397 A @acronym{POSIX} conformant archive will be created if @command{tar}
9398 was given @option{--format=posix} (@option{--format=pax}) option. No
9399 special option is required to read and extract from a @acronym{POSIX}
9403 * PAX keywords:: Controlling Extended Header Keywords.
9407 @subsubsection Controlling Extended Header Keywords
9411 @item --pax-option=@var{keyword-list}
9412 Handle keywords in @acronym{PAX} extended headers. This option is
9413 equivalent to @option{-o} option of the @command{pax} utility.
9416 @var{Keyword-list} is a comma-separated
9417 list of keyword options, each keyword option taking one of
9418 the following forms:
9421 @item delete=@var{pattern}
9422 When used with one of archive-creation commands,
9423 this option instructs @command{tar} to omit from extended header records
9424 that it produces any keywords matching the string @var{pattern}.
9426 When used in extract or list mode, this option instructs tar
9427 to ignore any keywords matching the given @var{pattern} in the extended
9428 header records. In both cases, matching is performed using the pattern
9429 matching notation described in @acronym{POSIX 1003.2}, 3.13
9430 (@pxref{wildcards}). For example:
9433 --pax-option delete=security.*
9436 would suppress security-related information.
9438 @item exthdr.name=@var{string}
9440 This keyword allows user control over the name that is written into the
9441 ustar header blocks for the extended headers. The name is obtained
9442 from @var{string} after making the following substitutions:
9444 @multitable @columnfractions .25 .55
9445 @headitem Meta-character @tab Replaced By
9446 @item %d @tab The directory name of the file, equivalent to the
9447 result of the @command{dirname} utility on the translated file name.
9448 @item %f @tab The name of the file with the directory information
9449 stripped, equivalent to the result of the @command{basename} utility
9450 on the translated file name.
9451 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9452 @item %% @tab A @samp{%} character.
9455 Any other @samp{%} characters in @var{string} produce undefined
9458 If no option @samp{exthdr.name=string} is specified, @command{tar}
9459 will use the following default value:
9465 @item exthdr.mtime=@var{value}
9467 This keyword defines the value of the @samp{mtime} field that
9468 is written into the ustar header blocks for the extended headers.
9469 By default, the @samp{mtime} field is set to the modification time
9470 of the archive member described by that extended headers.
9472 @item globexthdr.name=@var{string}
9473 This keyword allows user control over the name that is written into
9474 the ustar header blocks for global extended header records. The name
9475 is obtained from the contents of @var{string}, after making
9476 the following substitutions:
9478 @multitable @columnfractions .25 .55
9479 @headitem Meta-character @tab Replaced By
9480 @item %n @tab An integer that represents the
9481 sequence number of the global extended header record in the archive,
9483 @item %p @tab The process @acronym{ID} of the @command{tar} process.
9484 @item %% @tab A @samp{%} character.
9487 Any other @samp{%} characters in @var{string} produce undefined results.
9489 If no option @samp{globexthdr.name=string} is specified, @command{tar}
9490 will use the following default value:
9493 $TMPDIR/GlobalHead.%p.%n
9497 where @samp{$TMPDIR} represents the value of the @var{TMPDIR}
9498 environment variable. If @var{TMPDIR} is not set, @command{tar}
9501 @item exthdr.mtime=@var{value}
9503 This keyword defines the value of the @samp{mtime} field that
9504 is written into the ustar header blocks for the global extended headers.
9505 By default, the @samp{mtime} field is set to the time when
9506 @command{tar} was invoked.
9508 @item @var{keyword}=@var{value}
9509 When used with one of archive-creation commands, these keyword/value pairs
9510 will be included at the beginning of the archive in a global extended
9511 header record. When used with one of archive-reading commands,
9512 @command{tar} will behave as if it has encountered these keyword/value
9513 pairs at the beginning of the archive in a global extended header
9516 @item @var{keyword}:=@var{value}
9517 When used with one of archive-creation commands, these keyword/value pairs
9518 will be included as records at the beginning of an extended header for
9519 each file. This is effectively equivalent to @var{keyword}=@var{value}
9520 form except that it creates no global extended header records.
9522 When used with one of archive-reading commands, @command{tar} will
9523 behave as if these keyword/value pairs were included as records at the
9524 end of each extended header; thus, they will override any global or
9525 file-specific extended header record keywords of the same names.
9526 For example, in the command:
9529 tar --format=posix --create \
9530 --file archive --pax-option gname:=user .
9533 the group name will be forced to a new value for all files
9534 stored in the archive.
9537 In any of the forms described above, the @var{value} may be
9538 a string enclosed in curly braces. In that case, the string
9539 between the braces is understood either as a textual time
9540 representation, as described in @ref{Date input formats}, or a name of
9541 the existing file, starting with @samp{/} or @samp{.}. In the latter
9542 case, the modification time of that file is used.
9544 For example, to set all modification times to the current date, you
9545 use the following option:
9548 --pax-option='mtime:=@{now@}'
9551 Note quoting of the option's argument.
9553 @cindex archives, binary equivalent
9554 @cindex binary equivalent archives, creating
9555 As another example, here is the option that ensures that any two
9556 archives created using it, will be binary equivalent if they have the
9560 --pax-option=exthdr.name=%d/PaxHeaders/%f,atime:=0
9564 @subsection Checksumming Problems
9566 SunOS and HP-UX @command{tar} fail to accept archives created using
9567 @GNUTAR{} and containing non-@acronym{ASCII} file names, that
9568 is, file names having characters with the eight bit set, because they
9569 use signed checksums, while @GNUTAR{} uses unsigned
9570 checksums while creating archives, as per @acronym{POSIX} standards. On
9571 reading, @GNUTAR{} computes both checksums and
9572 accepts any. It is somewhat worrying that a lot of people may go
9573 around doing backup of their files using faulty (or at least
9574 non-standard) software, not learning about it until it's time to
9575 restore their missing files with an incompatible file extractor, or
9578 @GNUTAR{} compute checksums both ways, and accept
9579 any on read, so @acronym{GNU} tar can read Sun tapes even with their
9580 wrong checksums. @GNUTAR{} produces the standard
9581 checksum, however, raising incompatibilities with Sun. That is to
9582 say, @GNUTAR{} has not been modified to
9583 @emph{produce} incorrect archives to be read by buggy @command{tar}'s.
9584 I've been told that more recent Sun @command{tar} now read standard
9585 archives, so maybe Sun did a similar patch, after all?
9587 The story seems to be that when Sun first imported @command{tar}
9588 sources on their system, they recompiled it without realizing that
9589 the checksums were computed differently, because of a change in
9590 the default signing of @code{char}'s in their compiler. So they
9591 started computing checksums wrongly. When they later realized their
9592 mistake, they merely decided to stay compatible with it, and with
9593 themselves afterwards. Presumably, but I do not really know, HP-UX
9594 has chosen that their @command{tar} archives to be compatible with Sun's.
9595 The current standards do not favor Sun @command{tar} format. In any
9596 case, it now falls on the shoulders of SunOS and HP-UX users to get
9597 a @command{tar} able to read the good archives they receive.
9599 @node Large or Negative Values
9600 @subsection Large or Negative Values
9601 @cindex large values
9602 @cindex future time stamps
9603 @cindex negative time stamps
9606 The above sections suggest to use @samp{oldest possible} archive
9607 format if in doubt. However, sometimes it is not possible. If you
9608 attempt to archive a file whose metadata cannot be represented using
9609 required format, @GNUTAR{} will print error message and ignore such a
9610 file. You will than have to switch to a format that is able to
9611 handle such values. The format summary table (@pxref{Formats}) will
9614 In particular, when trying to archive files larger than 8GB or with
9615 timestamps not in the range 1970-01-01 00:00:00 through 2242-03-16
9616 12:56:31 @sc{utc}, you will have to chose between @acronym{GNU} and
9617 @acronym{POSIX} archive formats. When considering which format to
9618 choose, bear in mind that the @acronym{GNU} format uses
9619 two's-complement base-256 notation to store values that do not fit
9620 into standard @acronym{ustar} range. Such archives can generally be
9621 read only by a @GNUTAR{} implementation. Moreover, they sometimes
9622 cannot be correctly restored on another hosts even by @GNUTAR{}. For
9623 example, using two's complement representation for negative time
9624 stamps that assumes a signed 32-bit @code{time_t} generates archives
9625 that are not portable to hosts with differing @code{time_t}
9628 On the other hand, @acronym{POSIX} archives, generally speaking, can
9629 be extracted by any tar implementation that understands older
9630 @acronym{ustar} format. The only exception are files larger than 8GB.
9632 @FIXME{Describe how @acronym{POSIX} archives are extracted by non
9636 @subsection How to Extract GNU-Specific Data Using Other @command{tar} Implementations
9638 In previous sections you became acquainted with various quirks
9639 necessary to make your archives portable. Sometimes you may need to
9640 extract archives containing GNU-specific members using some
9641 third-party @command{tar} implementation or an older version of
9642 @GNUTAR{}. Of course your best bet is to have @GNUTAR{} installed,
9643 but if it is for some reason impossible, this section will explain
9644 how to cope without it.
9646 When we speak about @dfn{GNU-specific} members we mean two classes of
9647 them: members split between the volumes of a multi-volume archive and
9648 sparse members. You will be able to always recover such members if
9649 the archive is in PAX format. In addition split members can be
9650 recovered from archives in old GNU format. The following subsections
9651 describe the required procedures in detail.
9654 * Split Recovery:: Members Split Between Volumes
9655 * Sparse Recovery:: Sparse Members
9658 @node Split Recovery
9659 @subsubsection Extracting Members Split Between Volumes
9661 @cindex Mutli-volume archives, extracting using non-GNU tars
9662 If a member is split between several volumes of an old GNU format archive
9663 most third party @command{tar} implementation will fail to extract
9664 it. To extract it, use @command{tarcat} program (@pxref{Tarcat}).
9665 This program is available from
9666 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tarcat.html, @GNUTAR{}
9667 home page}. It concatenates several archive volumes into a single
9668 valid archive. For example, if you have three volumes named from
9669 @file{vol-1.tar} to @file{vol-3.tar}, you can do the following to
9670 extract them using a third-party @command{tar}:
9673 $ @kbd{tarcat vol-1.tar vol-2.tar vol-3.tar | tar xf -}
9676 @cindex Mutli-volume archives in PAX format, extracting using non-GNU tars
9677 You could use this approach for most (although not all) PAX
9678 format archives as well. However, extracting split members from a PAX
9679 archive is a much easier task, because PAX volumes are constructed in
9680 such a way that each part of a split member is extracted to a
9681 different file by @command{tar} implementations that are not aware of
9682 GNU extensions. More specifically, the very first part retains its
9683 original name, and all subsequent parts are named using the pattern:
9686 %d/GNUFileParts.%p/%f.%n
9690 where symbols preceeded by @samp{%} are @dfn{macro characters} that
9691 have the following meaning:
9693 @multitable @columnfractions .25 .55
9694 @headitem Meta-character @tab Replaced By
9695 @item %d @tab The directory name of the file, equivalent to the
9696 result of the @command{dirname} utility on its full name.
9697 @item %f @tab The file name of the file, equivalent to the result
9698 of the @command{basename} utility on its full name.
9699 @item %p @tab The process @acronym{ID} of the @command{tar} process that
9700 created the archive.
9701 @item %n @tab Ordinal number of this particular part.
9704 For example, if the file @file{var/longfile} was split during archive
9705 creation between three volumes, and the creator @command{tar} process
9706 had process @acronym{ID} @samp{27962}, then the member names will be:
9710 var/GNUFileParts.27962/longfile.1
9711 var/GNUFileParts.27962/longfile.2
9714 When you extract your archive using a third-party @command{tar}, these
9715 files will be created on your disk, and the only thing you will need
9716 to do to restore your file in its original form is concatenate them in
9717 the proper order, for example:
9722 $ @kbd{cat GNUFileParts.27962/longfile.1 \
9723 GNUFileParts.27962/longfile.2 >> longfile}
9724 $ rm -f GNUFileParts.27962
9728 Notice, that if the @command{tar} implementation you use supports PAX
9729 format archives, it will probably emit warnings about unknown keywords
9730 during extraction. They will look like this:
9735 Unknown extended header keyword 'GNU.volume.filename' ignored.
9736 Unknown extended header keyword 'GNU.volume.size' ignored.
9737 Unknown extended header keyword 'GNU.volume.offset' ignored.
9742 You can safely ignore these warnings.
9744 If your @command{tar} implementation is not PAX-aware, you will get
9745 more warnings and more files generated on your disk, e.g.:
9749 $ @kbd{tar xf vol-1.tar}
9750 var/PaxHeaders.27962/longfile: Unknown file type 'x', extracted as
9752 Unexpected EOF in archive
9753 $ @kbd{tar xf vol-2.tar}
9754 tmp/GlobalHead.27962.1: Unknown file type 'g', extracted as normal file
9755 GNUFileParts.27962/PaxHeaders.27962/sparsefile.1: Unknown file type
9756 'x', extracted as normal file
9760 Ignore these warnings. The @file{PaxHeaders.*} directories created
9761 will contain files with @dfn{extended header keywords} describing the
9762 extracted files. You can delete them, unless they describe sparse
9763 members. Read further to learn more about them.
9765 @node Sparse Recovery
9766 @subsubsection Extracting Sparse Members
9768 @cindex sparse files, extracting with non-GNU tars
9769 Any @command{tar} implementation will be able to extract sparse members from a
9770 PAX archive. However, the extracted files will be @dfn{condensed},
9771 i.e., any zero blocks will be removed from them. When we restore such
9772 a condensed file to its original form, by adding zero blocks (or
9773 @dfn{holes}) back to their original locations, we call this process
9774 @dfn{expanding} a compressed sparse file.
9777 To expand a file, you will need a simple auxiliary program called
9778 @command{xsparse}. It is available in source form from
9779 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/xsparse.html, @GNUTAR{}
9782 @cindex sparse files v.1.0, extracting with non-GNU tars
9783 Let's begin with archive members in @dfn{sparse format
9784 version 1.0}@footnote{@xref{PAX 1}.}, which are the easiest to expand.
9785 The condensed file will contain both file map and file data, so no
9786 additional data will be needed to restore it. If the original file
9787 name was @file{@var{dir}/@var{name}}, then the condensed file will be
9788 named @file{@var{dir}/@/GNUSparseFile.@var{n}/@/@var{name}}, where
9789 @var{n} is a decimal number@footnote{technically speaking, @var{n} is a
9790 @dfn{process @acronym{ID}} of the @command{tar} process which created the
9791 archive (@pxref{PAX keywords}).}.
9793 To expand a version 1.0 file, run @command{xsparse} as follows:
9796 $ @kbd{xsparse @file{cond-file}}
9800 where @file{cond-file} is the name of the condensed file. The utility
9801 will deduce the name for the resulting expanded file using the
9802 following algorithm:
9805 @item If @file{cond-file} does not contain any directories,
9806 @file{../cond-file} will be used;
9808 @item If @file{cond-file} has the form
9809 @file{@var{dir}/@var{t}/@var{name}}, where both @var{t} and @var{name}
9810 are simple names, with no @samp{/} characters in them, the output file
9811 name will be @file{@var{dir}/@var{name}}.
9813 @item Otherwise, if @file{cond-file} has the form
9814 @file{@var{dir}/@var{name}}, the output file name will be
9818 In the unlikely case when this algorithm does not suit your needs,
9819 you can explicitly specify output file name as a second argument to
9823 $ @kbd{xsparse @file{cond-file} @file{out-file}}
9826 It is often a good idea to run @command{xsparse} in @dfn{dry run} mode
9827 first. In this mode, the command does not actually expand the file,
9828 but verbosely lists all actions it would be taking to do so. The dry
9829 run mode is enabled by @option{-n} command line argument:
9833 $ @kbd{xsparse -n /home/gray/GNUSparseFile.6058/sparsefile}
9834 Reading v.1.0 sparse map
9835 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9836 `/home/gray/sparsefile'
9841 To actually expand the file, you would run:
9844 $ @kbd{xsparse /home/gray/GNUSparseFile.6058/sparsefile}
9848 The program behaves the same way all UNIX utilities do: it will keep
9849 quiet unless it has simething important to tell you (e.g. an error
9850 condition or something). If you wish it to produce verbose output,
9851 similar to that from the dry run mode, use @option{-v} option:
9855 $ @kbd{xsparse -v /home/gray/GNUSparseFile.6058/sparsefile}
9856 Reading v.1.0 sparse map
9857 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9858 `/home/gray/sparsefile'
9863 Additionally, if your @command{tar} implementation has extracted the
9864 @dfn{extended headers} for this file, you can instruct @command{xstar}
9865 to use them in order to verify the integrity of the expanded file.
9866 The option @option{-x} sets the name of the extended header file to
9867 use. Continuing our example:
9871 $ @kbd{xsparse -v -x /home/gray/PaxHeaders.6058/sparsefile \
9872 /home/gray/GNUSparseFile.6058/sparsefile}
9873 Reading extended header file
9874 Found variable GNU.sparse.major = 1
9875 Found variable GNU.sparse.minor = 0
9876 Found variable GNU.sparse.name = sparsefile
9877 Found variable GNU.sparse.realsize = 217481216
9878 Reading v.1.0 sparse map
9879 Expanding file `/home/gray/GNUSparseFile.6058/sparsefile' to
9880 `/home/gray/sparsefile'
9885 @anchor{extracting sparse v.0.x}
9886 @cindex sparse files v.0.1, extracting with non-GNU tars
9887 @cindex sparse files v.0.0, extracting with non-GNU tars
9888 An @dfn{extended header} is a special @command{tar} archive header
9889 that precedes an archive member and contains a set of
9890 @dfn{variables}, describing the member properties that cannot be
9891 stored in the standard @code{ustar} header. While optional for
9892 expanding sparse version 1.0 members, the use of extended headers is
9893 mandatory when expanding sparse members in older sparse formats: v.0.0
9894 and v.0.1 (The sparse formats are described in detail in @ref{Sparse
9895 Formats}.) So, for these formats, the question is: how to obtain
9896 extended headers from the archive?
9898 If you use a @command{tar} implementation that does not support PAX
9899 format, extended headers for each member will be extracted as a
9900 separate file. If we represent the member name as
9901 @file{@var{dir}/@var{name}}, then the extended header file will be
9902 named @file{@var{dir}/@/PaxHeaders.@var{n}/@/@var{name}}, where
9903 @var{n} is an integer number.
9905 Things become more difficult if your @command{tar} implementation
9906 does support PAX headers, because in this case you will have to
9907 manually extract the headers. We recommend the following algorithm:
9911 Consult the documentation of your @command{tar} implementation for an
9912 option that prints @dfn{block numbers} along with the archive
9913 listing (analogous to @GNUTAR{}'s @option{-R} option). For example,
9914 @command{star} has @option{-block-number}.
9917 Obtain verbose listing using the @samp{block number} option, and
9918 find block numbers of the sparse member in question and the member
9919 immediately following it. For example, running @command{star} on our
9924 $ @kbd{star -t -v -block-number -f arc.tar}
9926 star: Unknown extended header keyword 'GNU.sparse.size' ignored.
9927 star: Unknown extended header keyword 'GNU.sparse.numblocks' ignored.
9928 star: Unknown extended header keyword 'GNU.sparse.name' ignored.
9929 star: Unknown extended header keyword 'GNU.sparse.map' ignored.
9930 block 56: 425984 -rw-r--r-- gray/users Jun 25 14:46 2006 GNUSparseFile.28124/sparsefile
9931 block 897: 65391 -rw-r--r-- gray/users Jun 24 20:06 2006 README
9937 (as usual, ignore the warnings about unknown keywords.)
9940 Let @var{size} be the size of the sparse member, @var{Bs} be its block number
9941 and @var{Bn} be the block number of the next member.
9945 @var{N} = @var{Bs} - @var{Bn} - @var{size}/512 - 2
9949 This number gives the size of the extended header part in tar @dfn{blocks}.
9950 In our example, this formula gives: @code{897 - 56 - 425984 / 512 - 2
9954 Use @command{dd} to extract the headers:
9957 @kbd{dd if=@var{archive} of=@var{hname} bs=512 skip=@var{Bs} count=@var{N}}
9961 where @var{archive} is the archive name, @var{hname} is a name of the
9962 file to store the extended header in, @var{Bs} and @var{N} are
9963 computed in previous steps.
9965 In our example, this command will be
9968 $ @kbd{dd if=arc.tar of=xhdr bs=512 skip=56 count=7}
9972 Finally, you can expand the condensed file, using the obtained header:
9976 $ @kbd{xsparse -v -x xhdr GNUSparseFile.6058/sparsefile}
9977 Reading extended header file
9978 Found variable GNU.sparse.size = 217481216
9979 Found variable GNU.sparse.numblocks = 208
9980 Found variable GNU.sparse.name = sparsefile
9981 Found variable GNU.sparse.map = 0,2048,1050624,2048,@dots{}
9982 Expanding file `GNUSparseFile.28124/sparsefile' to `sparsefile'
9988 @section Comparison of @command{tar} and @command{cpio}
9991 @FIXME{Reorganize the following material}
9993 The @command{cpio} archive formats, like @command{tar}, do have maximum
9994 file name lengths. The binary and old @acronym{ASCII} formats have a maximum file
9995 length of 256, and the new @acronym{ASCII} and @acronym{CRC ASCII} formats have a max
9996 file length of 1024. @acronym{GNU} @command{cpio} can read and write archives
9997 with arbitrary file name lengths, but other @command{cpio} implementations
9998 may crash unexplainedly trying to read them.
10000 @command{tar} handles symbolic links in the form in which it comes in @acronym{BSD};
10001 @command{cpio} doesn't handle symbolic links in the form in which it comes
10002 in System V prior to SVR4, and some vendors may have added symlinks
10003 to their system without enhancing @command{cpio} to know about them.
10004 Others may have enhanced it in a way other than the way I did it
10005 at Sun, and which was adopted by AT&T (and which is, I think, also
10006 present in the @command{cpio} that Berkeley picked up from AT&T and put
10007 into a later @acronym{BSD} release---I think I gave them my changes).
10009 (SVR4 does some funny stuff with @command{tar}; basically, its @command{cpio}
10010 can handle @command{tar} format input, and write it on output, and it
10011 probably handles symbolic links. They may not have bothered doing
10012 anything to enhance @command{tar} as a result.)
10014 @command{cpio} handles special files; traditional @command{tar} doesn't.
10016 @command{tar} comes with V7, System III, System V, and @acronym{BSD} source;
10017 @command{cpio} comes only with System III, System V, and later @acronym{BSD}
10018 (4.3-tahoe and later).
10020 @command{tar}'s way of handling multiple hard links to a file can handle
10021 file systems that support 32-bit inumbers (e.g., the @acronym{BSD} file system);
10022 @command{cpio}s way requires you to play some games (in its ``binary''
10023 format, i-numbers are only 16 bits, and in its ``portable @acronym{ASCII}'' format,
10024 they're 18 bits---it would have to play games with the "file system @acronym{ID}"
10025 field of the header to make sure that the file system @acronym{ID}/i-number pairs
10026 of different files were always different), and I don't know which
10027 @command{cpio}s, if any, play those games. Those that don't might get
10028 confused and think two files are the same file when they're not, and
10029 make hard links between them.
10031 @command{tar}s way of handling multiple hard links to a file places only
10032 one copy of the link on the tape, but the name attached to that copy
10033 is the @emph{only} one you can use to retrieve the file; @command{cpio}s
10034 way puts one copy for every link, but you can retrieve it using any
10038 What type of check sum (if any) is used, and how is this calculated.
10041 See the attached manual pages for @command{tar} and @command{cpio} format.
10042 @command{tar} uses a checksum which is the sum of all the bytes in the
10043 @command{tar} header for a file; @command{cpio} uses no checksum.
10046 If anyone knows why @command{cpio} was made when @command{tar} was present
10050 It wasn't. @command{cpio} first showed up in PWB/UNIX 1.0; no
10051 generally-available version of UNIX had @command{tar} at the time. I don't
10052 know whether any version that was generally available @emph{within AT&T}
10053 had @command{tar}, or, if so, whether the people within AT&T who did
10054 @command{cpio} knew about it.
10056 On restore, if there is a corruption on a tape @command{tar} will stop at
10057 that point, while @command{cpio} will skip over it and try to restore the
10060 The main difference is just in the command syntax and header format.
10062 @command{tar} is a little more tape-oriented in that everything is blocked
10063 to start on a record boundary.
10066 Is there any differences between the ability to recover crashed
10067 archives between the two of them. (Is there any chance of recovering
10068 crashed archives at all.)
10071 Theoretically it should be easier under @command{tar} since the blocking
10072 lets you find a header with some variation of @samp{dd skip=@var{nn}}.
10073 However, modern @command{cpio}'s and variations have an option to just
10074 search for the next file header after an error with a reasonable chance
10075 of resyncing. However, lots of tape driver software won't allow you to
10076 continue past a media error which should be the only reason for getting
10077 out of sync unless a file changed sizes while you were writing the
10081 If anyone knows why @command{cpio} was made when @command{tar} was present
10082 at the unix scene, please tell me about this too.
10085 Probably because it is more media efficient (by not blocking everything
10086 and using only the space needed for the headers where @command{tar}
10087 always uses 512 bytes per file header) and it knows how to archive
10090 You might want to look at the freely available alternatives. The
10091 major ones are @command{afio}, @GNUTAR{}, and
10092 @command{pax}, each of which have their own extensions with some
10093 backwards compatibility.
10095 Sparse files were @command{tar}red as sparse files (which you can
10096 easily test, because the resulting archive gets smaller, and
10097 @acronym{GNU} @command{cpio} can no longer read it).
10100 @chapter Tapes and Other Archive Media
10103 A few special cases about tape handling warrant more detailed
10104 description. These special cases are discussed below.
10106 Many complexities surround the use of @command{tar} on tape drives. Since
10107 the creation and manipulation of archives located on magnetic tape was
10108 the original purpose of @command{tar}, it contains many features making
10109 such manipulation easier.
10111 Archives are usually written on dismountable media---tape cartridges,
10112 mag tapes, or floppy disks.
10114 The amount of data a tape or disk holds depends not only on its size,
10115 but also on how it is formatted. A 2400 foot long reel of mag tape
10116 holds 40 megabytes of data when formatted at 1600 bits per inch. The
10117 physically smaller EXABYTE tape cartridge holds 2.3 gigabytes.
10119 Magnetic media are re-usable---once the archive on a tape is no longer
10120 needed, the archive can be erased and the tape or disk used over.
10121 Media quality does deteriorate with use, however. Most tapes or disks
10122 should be discarded when they begin to produce data errors. EXABYTE
10123 tape cartridges should be discarded when they generate an @dfn{error
10124 count} (number of non-usable bits) of more than 10k.
10126 Magnetic media are written and erased using magnetic fields, and
10127 should be protected from such fields to avoid damage to stored data.
10128 Sticking a floppy disk to a filing cabinet using a magnet is probably
10132 * Device:: Device selection and switching
10133 * Remote Tape Server::
10134 * Common Problems and Solutions::
10135 * Blocking:: Blocking
10136 * Many:: Many archives on one tape
10137 * Using Multiple Tapes:: Using Multiple Tapes
10138 * label:: Including a Label in the Archive
10140 * Write Protection::
10144 @section Device Selection and Switching
10148 @item -f [@var{hostname}:]@var{file}
10149 @itemx --file=[@var{hostname}:]@var{file}
10150 Use archive file or device @var{file} on @var{hostname}.
10153 This option is used to specify the file name of the archive @command{tar}
10156 If the file name is @samp{-}, @command{tar} reads the archive from standard
10157 input (when listing or extracting), or writes it to standard output
10158 (when creating). If the @samp{-} file name is given when updating an
10159 archive, @command{tar} will read the original archive from its standard
10160 input, and will write the entire new archive to its standard output.
10162 If the file name contains a @samp{:}, it is interpreted as
10163 @samp{hostname:file name}. If the @var{hostname} contains an @dfn{at}
10164 sign (@samp{@@}), it is treated as @samp{user@@hostname:file name}. In
10165 either case, @command{tar} will invoke the command @command{rsh} (or
10166 @command{remsh}) to start up an @command{/usr/libexec/rmt} on the remote
10167 machine. If you give an alternate login name, it will be given to the
10169 Naturally, the remote machine must have an executable
10170 @command{/usr/libexec/rmt}. This program is free software from the
10171 University of California, and a copy of the source code can be found
10172 with the sources for @command{tar}; it's compiled and installed by default.
10173 The exact path to this utility is determined when configuring the package.
10174 It is @file{@var{prefix}/libexec/rmt}, where @var{prefix} stands for
10175 your installation prefix. This location may also be overridden at
10176 runtime by using @option{rmt-command=@var{command}} option (@xref{Option Summary,
10177 ---rmt-command}, for detailed description of this option. @xref{Remote
10178 Tape Server}, for the description of @command{rmt} command).
10180 If this option is not given, but the environment variable @env{TAPE}
10181 is set, its value is used; otherwise, old versions of @command{tar}
10182 used a default archive name (which was picked when @command{tar} was
10183 compiled). The default is normally set up to be the @dfn{first} tape
10184 drive or other transportable I/O medium on the system.
10186 Starting with version 1.11.5, @GNUTAR{} uses
10187 standard input and standard output as the default device, and I will
10188 not try anymore supporting automatic device detection at installation
10189 time. This was failing really in too many cases, it was hopeless.
10190 This is now completely left to the installer to override standard
10191 input and standard output for default device, if this seems
10192 preferable. Further, I think @emph{most} actual usages of
10193 @command{tar} are done with pipes or disks, not really tapes,
10194 cartridges or diskettes.
10196 Some users think that using standard input and output is running
10197 after trouble. This could lead to a nasty surprise on your screen if
10198 you forget to specify an output file name---especially if you are going
10199 through a network or terminal server capable of buffering large amounts
10200 of output. We had so many bug reports in that area of configuring
10201 default tapes automatically, and so many contradicting requests, that
10202 we finally consider the problem to be portably intractable. We could
10203 of course use something like @samp{/dev/tape} as a default, but this
10204 is @emph{also} running after various kind of trouble, going from hung
10205 processes to accidental destruction of real tapes. After having seen
10206 all this mess, using standard input and output as a default really
10207 sounds like the only clean choice left, and a very useful one too.
10209 @GNUTAR{} reads and writes archive in records, I
10210 suspect this is the main reason why block devices are preferred over
10211 character devices. Most probably, block devices are more efficient
10212 too. The installer could also check for @samp{DEFTAPE} in
10213 @file{<sys/mtio.h>}.
10216 @xopindex{force-local, short description}
10217 @item --force-local
10218 Archive file is local even if it contains a colon.
10220 @opindex rsh-command
10221 @item --rsh-command=@var{command}
10222 Use remote @var{command} instead of @command{rsh}. This option exists
10223 so that people who use something other than the standard @command{rsh}
10224 (e.g., a Kerberized @command{rsh}) can access a remote device.
10226 When this command is not used, the shell command found when
10227 the @command{tar} program was installed is used instead. This is
10228 the first found of @file{/usr/ucb/rsh}, @file{/usr/bin/remsh},
10229 @file{/usr/bin/rsh}, @file{/usr/bsd/rsh} or @file{/usr/bin/nsh}.
10230 The installer may have overridden this by defining the environment
10231 variable @env{RSH} @emph{at installation time}.
10234 Specify drive and density.
10236 @xopindex{multi-volume, short description}
10238 @itemx --multi-volume
10239 Create/list/extract multi-volume archive.
10241 This option causes @command{tar} to write a @dfn{multi-volume} archive---one
10242 that may be larger than will fit on the medium used to hold it.
10243 @xref{Multi-Volume Archives}.
10245 @xopindex{tape-length, short description}
10247 @itemx --tape-length=@var{num}
10248 Change tape after writing @var{num} x 1024 bytes.
10250 This option might be useful when your tape drivers do not properly
10251 detect end of physical tapes. By being slightly conservative on the
10252 maximum tape length, you might avoid the problem entirely.
10254 @xopindex{info-script, short description}
10255 @xopindex{new-volume-script, short description}
10256 @item -F @var{file}
10257 @itemx --info-script=@var{file}
10258 @itemx --new-volume-script=@var{file}
10259 Execute @file{file} at end of each tape. This implies
10260 @option{--multi-volume} (@option{-M}). @xref{info-script}, for a detailed
10261 description of this option.
10264 @node Remote Tape Server
10265 @section The Remote Tape Server
10267 @cindex remote tape drive
10269 In order to access the tape drive on a remote machine, @command{tar}
10270 uses the remote tape server written at the University of California at
10271 Berkeley. The remote tape server must be installed as
10272 @file{@var{prefix}/libexec/rmt} on any machine whose tape drive you
10273 want to use. @command{tar} calls @command{rmt} by running an
10274 @command{rsh} or @command{remsh} to the remote machine, optionally
10275 using a different login name if one is supplied.
10277 A copy of the source for the remote tape server is provided. It is
10278 Copyright @copyright{} 1983 by the Regents of the University of
10279 California, but can be freely distributed. It is compiled and
10280 installed by default.
10282 @cindex absolute file names
10283 Unless you use the @option{--absolute-names} (@option{-P}) option,
10284 @GNUTAR{} will not allow you to create an archive that contains
10285 absolute file names (a file name beginning with @samp{/}.) If you try,
10286 @command{tar} will automatically remove the leading @samp{/} from the
10287 file names it stores in the archive. It will also type a warning
10288 message telling you what it is doing.
10290 When reading an archive that was created with a different
10291 @command{tar} program, @GNUTAR{} automatically
10292 extracts entries in the archive which have absolute file names as if
10293 the file names were not absolute. This is an important feature. A
10294 visitor here once gave a @command{tar} tape to an operator to restore;
10295 the operator used Sun @command{tar} instead of @GNUTAR{},
10296 and the result was that it replaced large portions of
10297 our @file{/bin} and friends with versions from the tape; needless to
10298 say, we were unhappy about having to recover the file system from
10301 For example, if the archive contained a file @file{/usr/bin/computoy},
10302 @GNUTAR{} would extract the file to @file{usr/bin/computoy},
10303 relative to the current directory. If you want to extract the files in
10304 an archive to the same absolute names that they had when the archive
10305 was created, you should do a @samp{cd /} before extracting the files
10306 from the archive, or you should either use the @option{--absolute-names}
10307 option, or use the command @samp{tar -C / @dots{}}.
10309 @cindex Ultrix 3.1 and write failure
10310 Some versions of Unix (Ultrix 3.1 is known to have this problem),
10311 can claim that a short write near the end of a tape succeeded,
10312 when it actually failed. This will result in the -M option not
10313 working correctly. The best workaround at the moment is to use a
10314 significantly larger blocking factor than the default 20.
10316 In order to update an archive, @command{tar} must be able to backspace the
10317 archive in order to reread or rewrite a record that was just read (or
10318 written). This is currently possible only on two kinds of files: normal
10319 disk files (or any other file that can be backspaced with @samp{lseek}),
10320 and industry-standard 9-track magnetic tape (or any other kind of tape
10321 that can be backspaced with the @code{MTIOCTOP} @code{ioctl}.
10323 This means that the @option{--append}, @option{--concatenate}, and
10324 @option{--delete} commands will not work on any other kind of file.
10325 Some media simply cannot be backspaced, which means these commands and
10326 options will never be able to work on them. These non-backspacing
10327 media include pipes and cartridge tape drives.
10329 Some other media can be backspaced, and @command{tar} will work on them
10330 once @command{tar} is modified to do so.
10332 Archives created with the @option{--multi-volume}, @option{--label}, and
10333 @option{--incremental} (@option{-G}) options may not be readable by other version
10334 of @command{tar}. In particular, restoring a file that was split over
10335 a volume boundary will require some careful work with @command{dd}, if
10336 it can be done at all. Other versions of @command{tar} may also create
10337 an empty file whose name is that of the volume header. Some versions
10338 of @command{tar} may create normal files instead of directories archived
10339 with the @option{--incremental} (@option{-G}) option.
10341 @node Common Problems and Solutions
10342 @section Some Common Problems and their Solutions
10347 errors from system:
10349 no such file or directory
10352 errors from @command{tar}:
10353 directory checksum error
10354 header format error
10356 errors from media/system:
10368 @dfn{Block} and @dfn{record} terminology is rather confused, and it
10369 is also confusing to the expert reader. On the other hand, readers
10370 who are new to the field have a fresh mind, and they may safely skip
10371 the next two paragraphs, as the remainder of this manual uses those
10372 two terms in a quite consistent way.
10374 John Gilmore, the writer of the public domain @command{tar} from which
10375 @GNUTAR{} was originally derived, wrote (June 1995):
10378 The nomenclature of tape drives comes from IBM, where I believe
10379 they were invented for the IBM 650 or so. On IBM mainframes, what
10380 is recorded on tape are tape blocks. The logical organization of
10381 data is into records. There are various ways of putting records into
10382 blocks, including @code{F} (fixed sized records), @code{V} (variable
10383 sized records), @code{FB} (fixed blocked: fixed size records, @var{n}
10384 to a block), @code{VB} (variable size records, @var{n} to a block),
10385 @code{VSB} (variable spanned blocked: variable sized records that can
10386 occupy more than one block), etc. The @code{JCL} @samp{DD RECFORM=}
10387 parameter specified this to the operating system.
10389 The Unix man page on @command{tar} was totally confused about this.
10390 When I wrote @code{PD TAR}, I used the historically correct terminology
10391 (@command{tar} writes data records, which are grouped into blocks).
10392 It appears that the bogus terminology made it into @acronym{POSIX} (no surprise
10393 here), and now Fran@,{c}ois has migrated that terminology back
10394 into the source code too.
10397 The term @dfn{physical block} means the basic transfer chunk from or
10398 to a device, after which reading or writing may stop without anything
10399 being lost. In this manual, the term @dfn{block} usually refers to
10400 a disk physical block, @emph{assuming} that each disk block is 512
10401 bytes in length. It is true that some disk devices have different
10402 physical blocks, but @command{tar} ignore these differences in its own
10403 format, which is meant to be portable, so a @command{tar} block is always
10404 512 bytes in length, and @dfn{block} always mean a @command{tar} block.
10405 The term @dfn{logical block} often represents the basic chunk of
10406 allocation of many disk blocks as a single entity, which the operating
10407 system treats somewhat atomically; this concept is only barely used
10410 The term @dfn{physical record} is another way to speak of a physical
10411 block, those two terms are somewhat interchangeable. In this manual,
10412 the term @dfn{record} usually refers to a tape physical block,
10413 @emph{assuming} that the @command{tar} archive is kept on magnetic tape.
10414 It is true that archives may be put on disk or used with pipes,
10415 but nevertheless, @command{tar} tries to read and write the archive one
10416 @dfn{record} at a time, whatever the medium in use. One record is made
10417 up of an integral number of blocks, and this operation of putting many
10418 disk blocks into a single tape block is called @dfn{reblocking}, or
10419 more simply, @dfn{blocking}. The term @dfn{logical record} refers to
10420 the logical organization of many characters into something meaningful
10421 to the application. The term @dfn{unit record} describes a small set
10422 of characters which are transmitted whole to or by the application,
10423 and often refers to a line of text. Those two last terms are unrelated
10424 to what we call a @dfn{record} in @GNUTAR{}.
10426 When writing to tapes, @command{tar} writes the contents of the archive
10427 in chunks known as @dfn{records}. To change the default blocking
10428 factor, use the @option{--blocking-factor=@var{512-size}} (@option{-b
10429 @var{512-size}}) option. Each record will then be composed of
10430 @var{512-size} blocks. (Each @command{tar} block is 512 bytes.
10431 @xref{Standard}.) Each file written to the archive uses at least one
10432 full record. As a result, using a larger record size can result in
10433 more wasted space for small files. On the other hand, a larger record
10434 size can often be read and written much more efficiently.
10436 Further complicating the problem is that some tape drives ignore the
10437 blocking entirely. For these, a larger record size can still improve
10438 performance (because the software layers above the tape drive still
10439 honor the blocking), but not as dramatically as on tape drives that
10442 When reading an archive, @command{tar} can usually figure out the
10443 record size on itself. When this is the case, and a non-standard
10444 record size was used when the archive was created, @command{tar} will
10445 print a message about a non-standard blocking factor, and then operate
10446 normally. On some tape devices, however, @command{tar} cannot figure
10447 out the record size itself. On most of those, you can specify a
10448 blocking factor (with @option{--blocking-factor}) larger than the
10449 actual blocking factor, and then use the @option{--read-full-records}
10450 (@option{-B}) option. (If you specify a blocking factor with
10451 @option{--blocking-factor} and don't use the
10452 @option{--read-full-records} option, then @command{tar} will not
10453 attempt to figure out the recording size itself.) On some devices,
10454 you must always specify the record size exactly with
10455 @option{--blocking-factor} when reading, because @command{tar} cannot
10456 figure it out. In any case, use @option{--list} (@option{-t}) before
10457 doing any extractions to see whether @command{tar} is reading the archive
10460 @command{tar} blocks are all fixed size (512 bytes), and its scheme for
10461 putting them into records is to put a whole number of them (one or
10462 more) into each record. @command{tar} records are all the same size;
10463 at the end of the file there's a block containing all zeros, which
10464 is how you tell that the remainder of the last record(s) are garbage.
10466 In a standard @command{tar} file (no options), the block size is 512
10467 and the record size is 10240, for a blocking factor of 20. What the
10468 @option{--blocking-factor} option does is sets the blocking factor,
10469 changing the record size while leaving the block size at 512 bytes.
10470 20 was fine for ancient 800 or 1600 bpi reel-to-reel tape drives;
10471 most tape drives these days prefer much bigger records in order to
10472 stream and not waste tape. When writing tapes for myself, some tend
10473 to use a factor of the order of 2048, say, giving a record size of
10474 around one megabyte.
10476 If you use a blocking factor larger than 20, older @command{tar}
10477 programs might not be able to read the archive, so we recommend this
10478 as a limit to use in practice. @GNUTAR{}, however,
10479 will support arbitrarily large record sizes, limited only by the
10480 amount of virtual memory or the physical characteristics of the tape
10484 * Format Variations:: Format Variations
10485 * Blocking Factor:: The Blocking Factor of an Archive
10488 @node Format Variations
10489 @subsection Format Variations
10490 @cindex Format Parameters
10491 @cindex Format Options
10492 @cindex Options, archive format specifying
10493 @cindex Options, format specifying
10496 Format parameters specify how an archive is written on the archive
10497 media. The best choice of format parameters will vary depending on
10498 the type and number of files being archived, and on the media used to
10501 To specify format parameters when accessing or creating an archive,
10502 you can use the options described in the following sections.
10503 If you do not specify any format parameters, @command{tar} uses
10504 default parameters. You cannot modify a compressed archive.
10505 If you create an archive with the @option{--blocking-factor} option
10506 specified (@pxref{Blocking Factor}), you must specify that
10507 blocking-factor when operating on the archive. @xref{Formats}, for other
10508 examples of format parameter considerations.
10510 @node Blocking Factor
10511 @subsection The Blocking Factor of an Archive
10512 @cindex Blocking Factor
10513 @cindex Record Size
10514 @cindex Number of blocks per record
10515 @cindex Number of bytes per record
10516 @cindex Bytes per record
10517 @cindex Blocks per record
10520 @opindex blocking-factor
10521 The data in an archive is grouped into blocks, which are 512 bytes.
10522 Blocks are read and written in whole number multiples called
10523 @dfn{records}. The number of blocks in a record (i.e., the size of a
10524 record in units of 512 bytes) is called the @dfn{blocking factor}.
10525 The @option{--blocking-factor=@var{512-size}} (@option{-b
10526 @var{512-size}}) option specifies the blocking factor of an archive.
10527 The default blocking factor is typically 20 (i.e., 10240 bytes), but
10528 can be specified at installation. To find out the blocking factor of
10529 an existing archive, use @samp{tar --list --file=@var{archive-name}}.
10530 This may not work on some devices.
10532 Records are separated by gaps, which waste space on the archive media.
10533 If you are archiving on magnetic tape, using a larger blocking factor
10534 (and therefore larger records) provides faster throughput and allows you
10535 to fit more data on a tape (because there are fewer gaps). If you are
10536 archiving on cartridge, a very large blocking factor (say 126 or more)
10537 greatly increases performance. A smaller blocking factor, on the other
10538 hand, may be useful when archiving small files, to avoid archiving lots
10539 of nulls as @command{tar} fills out the archive to the end of the record.
10540 In general, the ideal record size depends on the size of the
10541 inter-record gaps on the tape you are using, and the average size of the
10542 files you are archiving. @xref{create}, for information on
10545 @FIXME{Need example of using a cartridge with blocking factor=126 or more.}
10547 Archives with blocking factors larger than 20 cannot be read
10548 by very old versions of @command{tar}, or by some newer versions
10549 of @command{tar} running on old machines with small address spaces.
10550 With @GNUTAR{}, the blocking factor of an archive is limited
10551 only by the maximum record size of the device containing the archive,
10552 or by the amount of available virtual memory.
10554 Also, on some systems, not using adequate blocking factors, as sometimes
10555 imposed by the device drivers, may yield unexpected diagnostics. For
10556 example, this has been reported:
10559 Cannot write to /dev/dlt: Invalid argument
10563 In such cases, it sometimes happen that the @command{tar} bundled by
10564 the system is aware of block size idiosyncrasies, while @GNUTAR{}
10565 requires an explicit specification for the block size,
10566 which it cannot guess. This yields some people to consider
10567 @GNUTAR{} is misbehaving, because by comparison,
10568 @cite{the bundle @command{tar} works OK}. Adding @w{@kbd{-b 256}},
10569 for example, might resolve the problem.
10571 If you use a non-default blocking factor when you create an archive, you
10572 must specify the same blocking factor when you modify that archive. Some
10573 archive devices will also require you to specify the blocking factor when
10574 reading that archive, however this is not typically the case. Usually, you
10575 can use @option{--list} (@option{-t}) without specifying a blocking factor---@command{tar}
10576 reports a non-default record size and then lists the archive members as
10577 it would normally. To extract files from an archive with a non-standard
10578 blocking factor (particularly if you're not sure what the blocking factor
10579 is), you can usually use the @option{--read-full-records} (@option{-B}) option while
10580 specifying a blocking factor larger then the blocking factor of the archive
10581 (i.e., @samp{tar --extract --read-full-records --blocking-factor=300}.
10582 @xref{list}, for more information on the @option{--list} (@option{-t})
10583 operation. @xref{Reading}, for a more detailed explanation of that option.
10586 @item --blocking-factor=@var{number}
10587 @itemx -b @var{number}
10588 Specifies the blocking factor of an archive. Can be used with any
10589 operation, but is usually not necessary with @option{--list} (@option{-t}).
10595 @item -b @var{blocks}
10596 @itemx --blocking-factor=@var{blocks}
10597 Set record size to @math{@var{blocks} * 512} bytes.
10599 This option is used to specify a @dfn{blocking factor} for the archive.
10600 When reading or writing the archive, @command{tar}, will do reads and writes
10601 of the archive in records of @math{@var{block}*512} bytes. This is true
10602 even when the archive is compressed. Some devices requires that all
10603 write operations be a multiple of a certain size, and so, @command{tar}
10604 pads the archive out to the next record boundary.
10606 The default blocking factor is set when @command{tar} is compiled, and is
10607 typically 20. Blocking factors larger than 20 cannot be read by very
10608 old versions of @command{tar}, or by some newer versions of @command{tar}
10609 running on old machines with small address spaces.
10611 With a magnetic tape, larger records give faster throughput and fit
10612 more data on a tape (because there are fewer inter-record gaps).
10613 If the archive is in a disk file or a pipe, you may want to specify
10614 a smaller blocking factor, since a large one will result in a large
10615 number of null bytes at the end of the archive.
10617 When writing cartridge or other streaming tapes, a much larger
10618 blocking factor (say 126 or more) will greatly increase performance.
10619 However, you must specify the same blocking factor when reading or
10620 updating the archive.
10622 Apparently, Exabyte drives have a physical block size of 8K bytes.
10623 If we choose our blocksize as a multiple of 8k bytes, then the problem
10624 seems to disappear. Id est, we are using block size of 112 right
10625 now, and we haven't had the problem since we switched@dots{}
10627 With @GNUTAR{} the blocking factor is limited only
10628 by the maximum record size of the device containing the archive, or by
10629 the amount of available virtual memory.
10631 However, deblocking or reblocking is virtually avoided in a special
10632 case which often occurs in practice, but which requires all the
10633 following conditions to be simultaneously true:
10636 the archive is subject to a compression option,
10638 the archive is not handled through standard input or output, nor
10639 redirected nor piped,
10641 the archive is directly handled to a local disk, instead of any special
10644 @option{--blocking-factor} is not explicitly specified on the @command{tar}
10648 If the output goes directly to a local disk, and not through
10649 stdout, then the last write is not extended to a full record size.
10650 Otherwise, reblocking occurs. Here are a few other remarks on this
10656 @command{gzip} will complain about trailing garbage if asked to
10657 uncompress a compressed archive on tape, there is an option to turn
10658 the message off, but it breaks the regularity of simply having to use
10659 @samp{@var{prog} -d} for decompression. It would be nice if gzip was
10660 silently ignoring any number of trailing zeros. I'll ask Jean-loup
10661 Gailly, by sending a copy of this message to him.
10664 @command{compress} does not show this problem, but as Jean-loup pointed
10665 out to Michael, @samp{compress -d} silently adds garbage after
10666 the result of decompression, which tar ignores because it already
10667 recognized its end-of-file indicator. So this bug may be safely
10671 @samp{gzip -d -q} will be silent about the trailing zeros indeed,
10672 but will still return an exit status of 2 which tar reports in turn.
10673 @command{tar} might ignore the exit status returned, but I hate doing
10674 that, as it weakens the protection @command{tar} offers users against
10675 other possible problems at decompression time. If @command{gzip} was
10676 silently skipping trailing zeros @emph{and} also avoiding setting the
10677 exit status in this innocuous case, that would solve this situation.
10680 @command{tar} should become more solid at not stopping to read a pipe at
10681 the first null block encountered. This inelegantly breaks the pipe.
10682 @command{tar} should rather drain the pipe out before exiting itself.
10685 @xopindex{ignore-zeros, short description}
10687 @itemx --ignore-zeros
10688 Ignore blocks of zeros in archive (means EOF).
10690 The @option{--ignore-zeros} (@option{-i}) option causes @command{tar} to ignore blocks
10691 of zeros in the archive. Normally a block of zeros indicates the
10692 end of the archive, but when reading a damaged archive, or one which
10693 was created by concatenating several archives together, this option
10694 allows @command{tar} to read the entire archive. This option is not on
10695 by default because many versions of @command{tar} write garbage after
10698 Note that this option causes @command{tar} to read to the end of the
10699 archive file, which may sometimes avoid problems when multiple files
10700 are stored on a single physical tape.
10702 @xopindex{read-full-records, short description}
10704 @itemx --read-full-records
10705 Reblock as we read (for reading 4.2@acronym{BSD} pipes).
10707 If @option{--read-full-records} is used, @command{tar}
10708 will not panic if an attempt to read a record from the archive does
10709 not return a full record. Instead, @command{tar} will keep reading
10710 until it has obtained a full
10713 This option is turned on by default when @command{tar} is reading
10714 an archive from standard input, or from a remote machine. This is
10715 because on @acronym{BSD} Unix systems, a read of a pipe will return however
10716 much happens to be in the pipe, even if it is less than @command{tar}
10717 requested. If this option was not used, @command{tar} would fail as
10718 soon as it read an incomplete record from the pipe.
10720 This option is also useful with the commands for updating an archive.
10726 @FIXME{Appropriate options should be moved here from elsewhere.}
10728 @cindex blocking factor
10729 @cindex tape blocking
10731 When handling various tapes or cartridges, you have to take care of
10732 selecting a proper blocking, that is, the number of disk blocks you
10733 put together as a single tape block on the tape, without intervening
10734 tape gaps. A @dfn{tape gap} is a small landing area on the tape
10735 with no information on it, used for decelerating the tape to a
10736 full stop, and for later regaining the reading or writing speed.
10737 When the tape driver starts reading a record, the record has to
10738 be read whole without stopping, as a tape gap is needed to stop the
10739 tape motion without loosing information.
10741 @cindex Exabyte blocking
10742 @cindex DAT blocking
10743 Using higher blocking (putting more disk blocks per tape block) will use
10744 the tape more efficiently as there will be less tape gaps. But reading
10745 such tapes may be more difficult for the system, as more memory will be
10746 required to receive at once the whole record. Further, if there is a
10747 reading error on a huge record, this is less likely that the system will
10748 succeed in recovering the information. So, blocking should not be too
10749 low, nor it should be too high. @command{tar} uses by default a blocking of
10750 20 for historical reasons, and it does not really matter when reading or
10751 writing to disk. Current tape technology would easily accommodate higher
10752 blockings. Sun recommends a blocking of 126 for Exabytes and 96 for DATs.
10753 We were told that for some DLT drives, the blocking should be a multiple
10754 of 4Kb, preferably 64Kb (@w{@kbd{-b 128}}) or 256 for decent performance.
10755 Other manufacturers may use different recommendations for the same tapes.
10756 This might also depends of the buffering techniques used inside modern
10757 tape controllers. Some imposes a minimum blocking, or a maximum blocking.
10758 Others request blocking to be some exponent of two.
10760 So, there is no fixed rule for blocking. But blocking at read time
10761 should ideally be the same as blocking used at write time. At one place
10762 I know, with a wide variety of equipment, they found it best to use a
10763 blocking of 32 to guarantee that their tapes are fully interchangeable.
10765 I was also told that, for recycled tapes, prior erasure (by the same
10766 drive unit that will be used to create the archives) sometimes lowers
10767 the error rates observed at rewriting time.
10769 I might also use @option{--number-blocks} instead of
10770 @option{--block-number}, so @option{--block} will then expand to
10771 @option{--blocking-factor} unambiguously.
10774 @section Many Archives on One Tape
10776 @FIXME{Appropriate options should be moved here from elsewhere.}
10778 @findex ntape @r{device}
10779 Most tape devices have two entries in the @file{/dev} directory, or
10780 entries that come in pairs, which differ only in the minor number for
10781 this device. Let's take for example @file{/dev/tape}, which often
10782 points to the only or usual tape device of a given system. There might
10783 be a corresponding @file{/dev/nrtape} or @file{/dev/ntape}. The simpler
10784 name is the @emph{rewinding} version of the device, while the name
10785 having @samp{nr} in it is the @emph{no rewinding} version of the same
10788 A rewinding tape device will bring back the tape to its beginning point
10789 automatically when this device is opened or closed. Since @command{tar}
10790 opens the archive file before using it and closes it afterwards, this
10791 means that a simple:
10794 $ @kbd{tar cf /dev/tape @var{directory}}
10798 will reposition the tape to its beginning both prior and after saving
10799 @var{directory} contents to it, thus erasing prior tape contents and
10800 making it so that any subsequent write operation will destroy what has
10803 @cindex tape positioning
10804 So, a rewinding device is normally meant to hold one and only one file.
10805 If you want to put more than one @command{tar} archive on a given tape, you
10806 will need to avoid using the rewinding version of the tape device. You
10807 will also have to pay special attention to tape positioning. Errors in
10808 positioning may overwrite the valuable data already on your tape. Many
10809 people, burnt by past experiences, will only use rewinding devices and
10810 limit themselves to one file per tape, precisely to avoid the risk of
10811 such errors. Be fully aware that writing at the wrong position on a
10812 tape loses all information past this point and most probably until the
10813 end of the tape, and this destroyed information @emph{cannot} be
10816 To save @var{directory-1} as a first archive at the beginning of a
10817 tape, and leave that tape ready for a second archive, you should use:
10820 $ @kbd{mt -f /dev/nrtape rewind}
10821 $ @kbd{tar cf /dev/nrtape @var{directory-1}}
10825 @dfn{Tape marks} are special magnetic patterns written on the tape
10826 media, which are later recognizable by the reading hardware. These
10827 marks are used after each file, when there are many on a single tape.
10828 An empty file (that is to say, two tape marks in a row) signal the
10829 logical end of the tape, after which no file exist. Usually,
10830 non-rewinding tape device drivers will react to the close request issued
10831 by @command{tar} by first writing two tape marks after your archive, and by
10832 backspacing over one of these. So, if you remove the tape at that time
10833 from the tape drive, it is properly terminated. But if you write
10834 another file at the current position, the second tape mark will be
10835 erased by the new information, leaving only one tape mark between files.
10837 So, you may now save @var{directory-2} as a second archive after the
10838 first on the same tape by issuing the command:
10841 $ @kbd{tar cf /dev/nrtape @var{directory-2}}
10845 and so on for all the archives you want to put on the same tape.
10847 Another usual case is that you do not write all the archives the same
10848 day, and you need to remove and store the tape between two archive
10849 sessions. In general, you must remember how many files are already
10850 saved on your tape. Suppose your tape already has 16 files on it, and
10851 that you are ready to write the 17th. You have to take care of skipping
10852 the first 16 tape marks before saving @var{directory-17}, say, by using
10856 $ @kbd{mt -f /dev/nrtape rewind}
10857 $ @kbd{mt -f /dev/nrtape fsf 16}
10858 $ @kbd{tar cf /dev/nrtape @var{directory-17}}
10861 In all the previous examples, we put aside blocking considerations, but
10862 you should do the proper things for that as well. @xref{Blocking}.
10865 * Tape Positioning:: Tape Positions and Tape Marks
10866 * mt:: The @command{mt} Utility
10869 @node Tape Positioning
10870 @subsection Tape Positions and Tape Marks
10873 Just as archives can store more than one file from the file system,
10874 tapes can store more than one archive file. To keep track of where
10875 archive files (or any other type of file stored on tape) begin and
10876 end, tape archive devices write magnetic @dfn{tape marks} on the
10877 archive media. Tape drives write one tape mark between files,
10878 two at the end of all the file entries.
10880 If you think of data as a series of records "rrrr"'s, and tape marks as
10881 "*"'s, a tape might look like the following:
10884 rrrr*rrrrrr*rrrrr*rr*rrrrr**-------------------------
10887 Tape devices read and write tapes using a read/write @dfn{tape
10888 head}---a physical part of the device which can only access one
10889 point on the tape at a time. When you use @command{tar} to read or
10890 write archive data from a tape device, the device will begin reading
10891 or writing from wherever on the tape the tape head happens to be,
10892 regardless of which archive or what part of the archive the tape
10893 head is on. Before writing an archive, you should make sure that no
10894 data on the tape will be overwritten (unless it is no longer needed).
10895 Before reading an archive, you should make sure the tape head is at
10896 the beginning of the archive you want to read. You can do it manually
10897 via @code{mt} utility (@pxref{mt}). The @code{restore} script does
10898 that automatically (@pxref{Scripted Restoration}).
10900 If you want to add new archive file entries to a tape, you should
10901 advance the tape to the end of the existing file entries, backspace
10902 over the last tape mark, and write the new archive file. If you were
10903 to add two archives to the example above, the tape might look like the
10907 rrrr*rrrrrr*rrrrr*rr*rrrrr*rrr*rrrr**----------------
10911 @subsection The @command{mt} Utility
10914 @FIXME{Is it true that this only works on non-block devices?
10915 should explain the difference, (fixed or variable).}
10916 @xref{Blocking Factor}.
10918 You can use the @command{mt} utility to advance or rewind a tape past a
10919 specified number of archive files on the tape. This will allow you
10920 to move to the beginning of an archive before extracting or reading
10921 it, or to the end of all the archives before writing a new one.
10922 @FIXME{Why isn't there an "advance 'til you find two tape marks
10925 The syntax of the @command{mt} command is:
10928 @kbd{mt [-f @var{tapename}] @var{operation} [@var{number}]}
10931 where @var{tapename} is the name of the tape device, @var{number} is
10932 the number of times an operation is performed (with a default of one),
10933 and @var{operation} is one of the following:
10935 @FIXME{is there any use for record operations?}
10940 Writes @var{number} tape marks at the current position on the tape.
10943 Moves tape position forward @var{number} files.
10946 Moves tape position back @var{number} files.
10949 Rewinds the tape. (Ignores @var{number}).
10953 Rewinds the tape and takes the tape device off-line. (Ignores @var{number}).
10956 Prints status information about the tape unit.
10960 If you don't specify a @var{tapename}, @command{mt} uses the environment
10961 variable @env{TAPE}; if @env{TAPE} is not set, @command{mt} will use
10962 the default device specified in your @file{sys/mtio.h} file
10963 (@code{DEFTAPE} variable). If this is not defined, the program will
10964 display a descriptive error message and exit with code 1.
10966 @command{mt} returns a 0 exit status when the operation(s) were
10967 successful, 1 if the command was unrecognized, and 2 if an operation
10970 @node Using Multiple Tapes
10971 @section Using Multiple Tapes
10973 Often you might want to write a large archive, one larger than will fit
10974 on the actual tape you are using. In such a case, you can run multiple
10975 @command{tar} commands, but this can be inconvenient, particularly if you
10976 are using options like @option{--exclude=@var{pattern}} or dumping entire file systems.
10977 Therefore, @command{tar} provides a special mode for creating
10978 multi-volume archives.
10980 @dfn{Multi-volume} archive is a single @command{tar} archive, stored
10981 on several media volumes of fixed size. Although in this section we will
10982 often call @samp{volume} a @dfn{tape}, there is absolutely no
10983 requirement for multi-volume archives to be stored on tapes. Instead,
10984 they can use whatever media type the user finds convenient, they can
10985 even be located on files.
10987 When creating a multi-volume archive, @GNUTAR{} continues to fill
10988 current volume until it runs out of space, then it switches to
10989 next volume (usually the operator is queried to replace the tape on
10990 this point), and continues working on the new volume. This operation
10991 continues until all requested files are dumped. If @GNUTAR{} detects
10992 end of media while dumping a file, such a file is archived in split
10993 form. Some very big files can even be split across several volumes.
10995 Each volume is itself a valid @GNUTAR{} archive, so it can be read
10996 without any special options. Consequently any file member residing
10997 entirely on one volume can be extracted or otherwise operated upon
10998 without needing the other volume. Sure enough, to extract a split
10999 member you would need all volumes its parts reside on.
11001 Multi-volume archives suffer from several limitations. In particular,
11002 they cannot be compressed.
11004 @GNUTAR{} is able to create multi-volume archives of two formats
11005 (@pxref{Formats}): @samp{GNU} and @samp{POSIX}.
11008 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
11009 * Tape Files:: Tape Files
11010 * Tarcat:: Concatenate Volumes into a Single Archive
11014 @node Multi-Volume Archives
11015 @subsection Archives Longer than One Tape or Disk
11016 @cindex Multi-volume archives
11018 @opindex multi-volume
11019 To create an archive that is larger than will fit on a single unit of
11020 the media, use the @option{--multi-volume} (@option{-M}) option in conjunction with
11021 the @option{--create} option (@pxref{create}). A @dfn{multi-volume}
11022 archive can be manipulated like any other archive (provided the
11023 @option{--multi-volume} option is specified), but is stored on more
11024 than one tape or disk.
11026 When you specify @option{--multi-volume}, @command{tar} does not report an
11027 error when it comes to the end of an archive volume (when reading), or
11028 the end of the media (when writing). Instead, it prompts you to load
11029 a new storage volume. If the archive is on a magnetic tape, you
11030 should change tapes when you see the prompt; if the archive is on a
11031 floppy disk, you should change disks; etc.
11034 @item --multi-volume
11036 Creates a multi-volume archive, when used in conjunction with
11037 @option{--create} (@option{-c}). To perform any other operation on a multi-volume
11038 archive, specify @option{--multi-volume} in conjunction with that
11043 $ @kbd{tar --create --multi-volume --file=/dev/tape @var{files}}
11047 The method @command{tar} uses to detect end of tape is not perfect, and
11048 fails on some operating systems or on some devices. If @command{tar}
11049 cannot detect the end of the tape itself, you can use
11050 @option{--tape-length} option to inform it about the capacity of the
11053 @anchor{tape-length}
11055 @opindex tape-length
11056 @item --tape-length=@var{size}
11057 @itemx -L @var{size}
11058 Set maximum length of a volume. The @var{size} argument should then
11059 be the usable size of the tape in units of 1024 bytes. This option
11060 selects @option{--multi-volume} automatically. For example:
11063 $ @kbd{tar --create --tape-length=41943040 --file=/dev/tape @var{files}}
11067 @anchor{change volume prompt}
11068 When @GNUTAR{} comes to the end of a storage media, it asks you to
11069 change the volume. The built-in prompt for POSIX locale
11070 is@footnote{If you run @GNUTAR{} under a different locale, the
11071 translation to the locale's language will be used.}:
11074 Prepare volume #@var{n} for `@var{archive}' and hit return:
11078 where @var{n} is the ordinal number of the volume to be created and
11079 @var{archive} is archive file or device name.
11081 When prompting for a new tape, @command{tar} accepts any of the following
11086 Request @command{tar} to explain possible responses
11088 Request @command{tar} to exit immediately.
11089 @item n @var{file-name}
11090 Request @command{tar} to write the next volume on the file @var{file-name}.
11092 Request @command{tar} to run a subshell. This option can be disabled
11093 by giving @option{--restrict} command line option to
11094 @command{tar}@footnote{@xref{--restrict}, for more information about
11097 Request @command{tar} to begin writing the next volume.
11100 (You should only type @samp{y} after you have changed the tape;
11101 otherwise @command{tar} will write over the volume it just finished.)
11103 @cindex Volume number file
11105 @anchor{volno-file}
11106 @opindex volno-file
11107 The volume number used by @command{tar} in its tape-changing prompt
11108 can be changed; if you give the
11109 @option{--volno-file=@var{file-of-number}} option, then
11110 @var{file-of-number} should be an non-existing file to be created, or
11111 else, a file already containing a decimal number. That number will be
11112 used as the volume number of the first volume written. When
11113 @command{tar} is finished, it will rewrite the file with the
11114 now-current volume number. (This does not change the volume number
11115 written on a tape label, as per @ref{label}, it @emph{only} affects
11116 the number used in the prompt.)
11118 @cindex End-of-archive info script
11119 @cindex Info script
11120 @anchor{info-script}
11121 @opindex info-script
11122 @opindex new-volume-script
11123 If you want more elaborate behavior than this, you can write a special
11124 @dfn{new volume script}, that will be responsible for changing the
11125 volume, and instruct @command{tar} to use it instead of its normal
11126 prompting procedure:
11129 @item --info-script=@var{script-name}
11130 @itemx --new-volume-script=@var{script-name}
11131 @itemx -F @var{script-name}
11132 Specify the full name of the volume script to use. The script can be
11133 used to eject cassettes, or to broadcast messages such as
11134 @samp{Someone please come change my tape} when performing unattended
11138 The @var{script-name} is executed without any command line
11139 arguments. It inherits @command{tar}'s shell environment.
11140 Additional data is passed to it via the following
11141 environment variables:
11144 @vrindex TAR_VERSION, info script environment variable
11146 @GNUTAR{} version number.
11148 @vrindex TAR_ARCHIVE, info script environment variable
11150 The name of the archive @command{tar} is processing.
11152 @vrindex TAR_BLOCKING_FACTOR, info script environment variable
11153 @item TAR_BLOCKING_FACTOR
11154 Current blocking factor (@pxref{Blocking}.
11156 @vrindex TAR_VOLUME, info script environment variable
11158 Ordinal number of the volume @command{tar} is about to start.
11160 @vrindex TAR_SUBCOMMAND, info script environment variable
11161 @item TAR_SUBCOMMAND
11162 A short option describing the operation @command{tar} is executing
11163 @xref{Operations}, for a complete list of subcommand options.
11165 @vrindex TAR_FORMAT, info script environment variable
11167 Format of the archive being processed. @xref{Formats}, for a complete
11168 list of archive format names.
11170 @vrindex TAR_FD, info script environment variable
11172 File descriptor which can be used to communicate the new volume
11173 name to @command{tar}.
11176 The volume script can instruct @command{tar} to use new archive name,
11177 by writing in to file descriptor @env{$TAR_FD} (see below for an example).
11179 If the info script fails, @command{tar} exits; otherwise, it begins
11180 writing the next volume.
11182 If you want @command{tar} to cycle through a series of files or tape
11183 drives, there are three approaches to choose from. First of all, you
11184 can give @command{tar} multiple @option{--file} options. In this case
11185 the specified files will be used, in sequence, as the successive
11186 volumes of the archive. Only when the first one in the sequence needs
11187 to be used again will @command{tar} prompt for a tape change (or run
11188 the info script). For example, suppose someone has two tape drives on
11189 a system named @file{/dev/tape0} and @file{/dev/tape1}. For having
11190 @GNUTAR{} to switch to the second drive when it needs to write the
11191 second tape, and then back to the first tape, etc., just do either of:
11194 $ @kbd{tar --create --multi-volume --file=/dev/tape0 --file=/dev/tape1 @var{files}}
11195 $ @kbd{tar cMff /dev/tape0 /dev/tape1 @var{files}}
11198 The second method is to use the @samp{n} response to the tape-change
11201 Finally, the most flexible approach is to use a volume script, that
11202 writes new archive name to the file descriptor @env{$TAR_FD}. For example, the
11203 following volume script will create a series of archive files, named
11204 @file{@var{archive}-@var{vol}}, where @var{archive} is the name of the
11205 archive being created (as given by @option{--file} option) and
11206 @var{vol} is the ordinal number of the archive being created:
11211 echo Preparing volume $TAR_VOLUME of $TAR_ARCHIVE.
11213 name=`expr $TAR_ARCHIVE : '\(.*\)-.*'`
11214 case $TAR_SUBCOMMAND in
11216 -d|-x|-t) test -r $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME || exit 1
11221 echo $@{name:-$TAR_ARCHIVE@}-$TAR_VOLUME >&$TAR_FD
11225 The same script can be used while listing, comparing or extracting
11226 from the created archive. For example:
11230 # @r{Create a multi-volume archive:}
11231 $ @kbd{tar -c -L1024 -f archive.tar -F new-volume .}
11232 # @r{Extract from the created archive:}
11233 $ @kbd{tar -x -f archive.tar -F new-volume .}
11238 Notice, that the first command had to use @option{-L} option, since
11239 otherwise @GNUTAR{} will end up writing everything to file
11240 @file{archive.tar}.
11242 You can read each individual volume of a multi-volume archive as if it
11243 were an archive by itself. For example, to list the contents of one
11244 volume, use @option{--list}, without @option{--multi-volume} specified.
11245 To extract an archive member from one volume (assuming it is described
11246 that volume), use @option{--extract}, again without
11247 @option{--multi-volume}.
11249 If an archive member is split across volumes (i.e., its entry begins on
11250 one volume of the media and ends on another), you need to specify
11251 @option{--multi-volume} to extract it successfully. In this case, you
11252 should load the volume where the archive member starts, and use
11253 @samp{tar --extract --multi-volume}---@command{tar} will prompt for later
11254 volumes as it needs them. @xref{extracting archives}, for more
11255 information about extracting archives.
11257 Multi-volume archives can be modified like any other archive. To add
11258 files to a multi-volume archive, you need to only mount the last
11259 volume of the archive media (and new volumes, if needed). For all
11260 other operations, you need to use the entire archive.
11262 If a multi-volume archive was labeled using
11263 @option{--label=@var{archive-label}} (@pxref{label}) when it was
11264 created, @command{tar} will not automatically label volumes which are
11265 added later. To label subsequent volumes, specify
11266 @option{--label=@var{archive-label}} again in conjunction with the
11267 @option{--append}, @option{--update} or @option{--concatenate} operation.
11269 Notice that multi-volume support is a GNU extension and the archives
11270 created in this mode should be read only using @GNUTAR{}. If you
11271 absolutely have to process such archives using a third-party @command{tar}
11272 implementation, read @ref{Split Recovery}.
11275 @subsection Tape Files
11276 @cindex labeling archives
11280 To give the archive a name which will be recorded in it, use the
11281 @option{--label=@var{volume-label}} (@option{-V @var{volume-label}})
11282 option. This will write a special block identifying
11283 @var{volume-label} as the name of the archive to the front of the
11284 archive which will be displayed when the archive is listed with
11285 @option{--list}. If you are creating a multi-volume archive with
11286 @option{--multi-volume} (@pxref{Using Multiple Tapes}), then the
11287 volume label will have @samp{Volume @var{nnn}} appended to the name
11288 you give, where @var{nnn} is the number of the volume of the archive.
11289 (If you use the @option{--label=@var{volume-label}}) option when
11290 reading an archive, it checks to make sure the label on the tape
11291 matches the one you give. @xref{label}.
11293 When @command{tar} writes an archive to tape, it creates a single
11294 tape file. If multiple archives are written to the same tape, one
11295 after the other, they each get written as separate tape files. When
11296 extracting, it is necessary to position the tape at the right place
11297 before running @command{tar}. To do this, use the @command{mt} command.
11298 For more information on the @command{mt} command and on the organization
11299 of tapes into a sequence of tape files, see @ref{mt}.
11301 People seem to often do:
11304 @kbd{--label="@var{some-prefix} `date +@var{some-format}`"}
11307 or such, for pushing a common date in all volumes or an archive set.
11310 @subsection Concatenate Volumes into a Single Archive
11313 Sometimes it is necessary to convert existing @GNUTAR{} multi-volume
11314 archive to a single @command{tar} archive. Simply concatenating all
11315 volumes into one will not work, since each volume carries an additional
11316 information at the beginning. @GNUTAR{} is shipped with the shell
11317 script @command{tarcat} designed for this purpose.
11319 The script takes a list of files comprising a multi-volume archive
11320 and creates the resulting archive at the standard output. For example:
11323 @kbd{tarcat vol.1 vol.2 vol.3 | tar tf -}
11326 The script implements a simple heuristics to determine the format of
11327 the first volume file and to decide how to process the rest of the
11328 files. However, it makes no attempt to verify whether the files are
11329 given in order or even if they are valid @command{tar} archives.
11330 It uses @command{dd} and does not filter its standard error, so you
11331 will usually see lots of spurious messages.
11333 @FIXME{The script is not installed. Should we install it?}
11336 @section Including a Label in the Archive
11337 @cindex Labeling an archive
11338 @cindex Labels on the archive media
11339 @cindex Labeling multi-volume archives
11343 To avoid problems caused by misplaced paper labels on the archive
11344 media, you can include a @dfn{label} entry---an archive member which
11345 contains the name of the archive---in the archive itself. Use the
11346 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11347 option in conjunction with the @option{--create} operation to include
11348 a label entry in the archive as it is being created.
11351 @item --label=@var{archive-label}
11352 @itemx -V @var{archive-label}
11353 Includes an @dfn{archive-label} at the beginning of the archive when
11354 the archive is being created, when used in conjunction with the
11355 @option{--create} operation. Checks to make sure the archive label
11356 matches the one specified (when used in conjunction with any other
11360 If you create an archive using both
11361 @option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
11362 and @option{--multi-volume} (@option{-M}), each volume of the archive
11363 will have an archive label of the form @samp{@var{archive-label}
11364 Volume @var{n}}, where @var{n} is 1 for the first volume, 2 for the
11365 next, and so on. @xref{Using Multiple Tapes}, for information on
11366 creating multiple volume archives.
11368 @cindex Volume label, listing
11369 @cindex Listing volume label
11370 The volume label will be displayed by @option{--list} along with
11371 the file contents. If verbose display is requested, it will also be
11372 explicitly marked as in the example below:
11376 $ @kbd{tar --verbose --list --file=iamanarchive}
11377 V--------- 0 0 0 1992-03-07 12:01 iamalabel--Volume Header--
11378 -rw-r--r-- ringo user 40 1990-05-21 13:30 iamafilename
11382 @opindex test-label
11383 @anchor{--test-label option}
11384 However, @option{--list} option will cause listing entire
11385 contents of the archive, which may be undesirable (for example, if the
11386 archive is stored on a tape). You can request checking only the volume
11387 by specifying @option{--test-label} option. This option reads only the
11388 first block of an archive, so it can be used with slow storage
11389 devices. For example:
11393 $ @kbd{tar --test-label --file=iamanarchive}
11398 If @option{--test-label} is used with a single command line
11399 argument, @command{tar} compares the volume label with the
11400 argument. It exits with code 0 if the two strings match, and with code
11401 2 otherwise. In this case no output is displayed. For example:
11405 $ @kbd{tar --test-label --file=iamanarchive 'iamalable'}
11407 $ @kbd{tar --test-label --file=iamanarchive 'iamalable' alabel}
11412 If you request any operation, other than @option{--create}, along
11413 with using @option{--label} option, @command{tar} will first check if
11414 the archive label matches the one specified and will refuse to proceed
11415 if it does not. Use this as a safety precaution to avoid accidentally
11416 overwriting existing archives. For example, if you wish to add files
11417 to @file{archive}, presumably labeled with string @samp{My volume},
11422 $ @kbd{tar -rf archive --label 'My volume' .}
11423 tar: Archive not labeled to match `My volume'
11428 in case its label does not match. This will work even if
11429 @file{archive} is not labeled at all.
11431 Similarly, @command{tar} will refuse to list or extract the
11432 archive if its label doesn't match the @var{archive-label}
11433 specified. In those cases, @var{archive-label} argument is interpreted
11434 as a globbing-style pattern which must match the actual magnetic
11435 volume label. @xref{exclude}, for a precise description of how match
11436 is attempted@footnote{Previous versions of @command{tar} used full
11437 regular expression matching, or before that, only exact string
11438 matching, instead of wildcard matchers. We decided for the sake of
11439 simplicity to use a uniform matching device through
11440 @command{tar}.}. If the switch @option{--multi-volume} (@option{-M}) is being used,
11441 the volume label matcher will also suffix @var{archive-label} by
11442 @w{@samp{ Volume [1-9]*}} if the initial match fails, before giving
11443 up. Since the volume numbering is automatically added in labels at
11444 creation time, it sounded logical to equally help the user taking care
11445 of it when the archive is being read.
11447 The @option{--label} was once called @option{--volume}, but is not
11448 available under that name anymore.
11450 You can also use @option{--label} to get a common information on
11451 all tapes of a series. For having this information different in each
11452 series created through a single script used on a regular basis, just
11453 manage to get some date string as part of the label. For example:
11457 $ @kbd{tar cfMV /dev/tape "Daily backup for `date +%Y-%m-%d`"}
11458 $ @kbd{tar --create --file=/dev/tape --multi-volume \
11459 --volume="Daily backup for `date +%Y-%m-%d`"}
11463 Also note that each label has its own date and time, which corresponds
11464 to when @GNUTAR{} initially attempted to write it,
11465 often soon after the operator launches @command{tar} or types the
11466 carriage return telling that the next tape is ready. Comparing date
11467 labels does give an idea of tape throughput only if the delays for
11468 rewinding tapes and the operator switching them were negligible, which
11469 is usually not the case.
11472 @section Verifying Data as It is Stored
11473 @cindex Verifying a write operation
11474 @cindex Double-checking a write operation
11479 @opindex verify, short description
11480 Attempt to verify the archive after writing.
11483 This option causes @command{tar} to verify the archive after writing it.
11484 Each volume is checked after it is written, and any discrepancies
11485 are recorded on the standard error output.
11487 Verification requires that the archive be on a back-space-able medium.
11488 This means pipes, some cartridge tape drives, and some other devices
11489 cannot be verified.
11491 You can insure the accuracy of an archive by comparing files in the
11492 system with archive members. @command{tar} can compare an archive to the
11493 file system as the archive is being written, to verify a write
11494 operation, or can compare a previously written archive, to insure that
11497 @xopindex{verify, using with @option{--create}}
11498 @xopindex{create, using with @option{--verify}}
11499 To check for discrepancies in an archive immediately after it is
11500 written, use the @option{--verify} (@option{-W}) option in conjunction with
11501 the @option{--create} operation. When this option is
11502 specified, @command{tar} checks archive members against their counterparts
11503 in the file system, and reports discrepancies on the standard error.
11505 To verify an archive, you must be able to read it from before the end
11506 of the last written entry. This option is useful for detecting data
11507 errors on some tapes. Archives written to pipes, some cartridge tape
11508 drives, and some other devices cannot be verified.
11510 One can explicitly compare an already made archive with the file
11511 system by using the @option{--compare} (@option{--diff}, @option{-d})
11512 option, instead of using the more automatic @option{--verify} option.
11515 Note that these two options have a slightly different intent. The
11516 @option{--compare} option checks how identical are the logical contents of some
11517 archive with what is on your disks, while the @option{--verify} option is
11518 really for checking if the physical contents agree and if the recording
11519 media itself is of dependable quality. So, for the @option{--verify}
11520 operation, @command{tar} tries to defeat all in-memory cache pertaining to
11521 the archive, while it lets the speed optimization undisturbed for the
11522 @option{--compare} option. If you nevertheless use @option{--compare} for
11523 media verification, you may have to defeat the in-memory cache yourself,
11524 maybe by opening and reclosing the door latch of your recording unit,
11525 forcing some doubt in your operating system about the fact this is really
11526 the same volume as the one just written or read.
11528 The @option{--verify} option would not be necessary if drivers were indeed
11529 able to detect dependably all write failures. This sometimes require many
11530 magnetic heads, some able to read after the writes occurred. One would
11531 not say that drivers unable to detect all cases are necessarily flawed,
11532 as long as programming is concerned.
11534 The @option{--verify} (@option{-W}) option will not work in
11535 conjunction with the @option{--multi-volume} (@option{-M}) option or
11536 the @option{--append} (@option{-r}), @option{--update} (@option{-u})
11537 and @option{--delete} operations. @xref{Operations}, for more
11538 information on these operations.
11540 Also, since @command{tar} normally strips leading @samp{/} from file
11541 names (@pxref{absolute}), a command like @samp{tar --verify -cf
11542 /tmp/foo.tar /etc} will work as desired only if the working directory is
11543 @file{/}, as @command{tar} uses the archive's relative member names
11544 (e.g., @file{etc/motd}) when verifying the archive.
11546 @node Write Protection
11547 @section Write Protection
11549 Almost all tapes and diskettes, and in a few rare cases, even disks can
11550 be @dfn{write protected}, to protect data on them from being changed.
11551 Once an archive is written, you should write protect the media to prevent
11552 the archive from being accidentally overwritten or deleted. (This will
11553 protect the archive from being changed with a tape or floppy drive---it
11554 will not protect it from magnet fields or other physical hazards).
11556 The write protection device itself is usually an integral part of the
11557 physical media, and can be a two position (write enabled/write
11558 disabled) switch, a notch which can be popped out or covered, a ring
11559 which can be removed from the center of a tape reel, or some other
11560 changeable feature.
11565 This appendix lists some important user-visible changes between
11566 version @GNUTAR{} @value{VERSION} and previous versions. An up-to-date
11567 version of this document is available at
11568 @uref{http://www.gnu.org/@/software/@/tar/manual/changes.html,the
11569 @GNUTAR{} documentation page}.
11572 @item Use of globbing patterns when listing and extracting.
11574 Previous versions of GNU tar assumed shell-style globbing when
11575 extracting from or listing an archive. For example:
11578 $ @kbd{tar xf foo.tar '*.c'}
11581 would extract all files whose names end in @samp{.c}. This behavior
11582 was not documented and was incompatible with traditional tar
11583 implementations. Therefore, starting from version 1.15.91, GNU tar
11584 no longer uses globbing by default. For example, the above invocation
11585 is now interpreted as a request to extract from the archive the file
11588 To facilitate transition to the new behavior for those users who got
11589 used to the previous incorrect one, @command{tar} will print a warning
11590 if it finds out that a requested member was not found in the archive
11591 and its name looks like a globbing pattern. For example:
11594 $ @kbd{tar xf foo.tar '*.c'}
11595 tar: Pattern matching characters used in file names. Please,
11596 tar: use --wildcards to enable pattern matching, or --no-wildcards to
11597 tar: suppress this warning.
11598 tar: *.c: Not found in archive
11599 tar: Error exit delayed from previous errors
11602 To treat member names as globbing patterns, use --wildcards option.
11603 If you want to tar to mimic the behavior of versions prior to 1.15.91,
11604 add this option to your @env{TAR_OPTIONS} variable.
11606 @xref{wildcards}, for the detailed discussion of the use of globbing
11607 patterns by @GNUTAR{}.
11609 @item Use of short option @option{-o}.
11611 Earlier versions of @GNUTAR{} understood @option{-o} command line
11612 option as a synonym for @option{--old-archive}.
11614 @GNUTAR{} starting from version 1.13.90 understands this option as
11615 a synonym for @option{--no-same-owner}. This is compatible with
11616 UNIX98 @command{tar} implementations.
11618 However, to facilitate transition, @option{-o} option retains its
11619 old semantics when it is used with one of archive-creation commands.
11620 Users are encouraged to use @option{--format=oldgnu} instead.
11622 It is especially important, since versions of @acronym{GNU} Automake
11623 up to and including 1.8.4 invoke tar with this option to produce
11624 distribution tarballs. @xref{Formats,v7}, for the detailed discussion
11625 of this issue and its implications.
11627 @xref{Options, tar-formats, Changing Automake's Behavior,
11628 automake, GNU Automake}, for a description on how to use various
11629 archive formats with @command{automake}.
11631 Future versions of @GNUTAR{} will understand @option{-o} only as a
11632 synonym for @option{--no-same-owner}.
11634 @item Use of short option @option{-l}
11636 Earlier versions of @GNUTAR{} understood @option{-l} option as a
11637 synonym for @option{--one-file-system}. Since such usage contradicted
11638 to UNIX98 specification and harmed compatibility with other
11639 implementation, it was declared deprecated in version 1.14. However,
11640 to facilitate transition to its new semantics, it was supported by
11641 versions 1.15 and 1.15.90. The present use of @option{-l} as a short
11642 variant of @option{--check-links} was introduced in version 1.15.91.
11644 @item Use of options @option{--portability} and @option{--old-archive}
11646 These options are deprecated. Please use @option{--format=v7} instead.
11648 @item Use of option @option{--posix}
11650 This option is deprecated. Please use @option{--format=posix} instead.
11653 @node Configuring Help Summary
11654 @appendix Configuring Help Summary
11656 Running @kbd{tar --help} displays the short @command{tar} option
11657 summary (@pxref{help}). This summary is organized by @dfn{groups} of
11658 semantically close options. The options within each group are printed
11659 in the following order: a short option, eventually followed by a list
11660 of corresponding long option names, followed by a short description of
11661 the option. For example, here is an excerpt from the actual @kbd{tar
11665 Main operation mode:
11667 -A, --catenate, --concatenate append tar files to an archive
11668 -c, --create create a new archive
11669 -d, --diff, --compare find differences between archive and
11671 --delete delete from the archive
11674 @vrindex ARGP_HELP_FMT, environment variable
11675 The exact visual representation of the help output is configurable via
11676 @env{ARGP_HELP_FMT} environment variable. The value of this variable
11677 is a comma-separated list of @dfn{format variable} assignments. There
11678 are two kinds of format variables. An @dfn{offset variable} keeps the
11679 offset of some part of help output text from the leftmost column on
11680 the screen. A @dfn{boolean} variable is a flag that toggles some
11681 output feature on or off. Depending on the type of the corresponding
11682 variable, there are two kinds of assignments:
11685 @item Offset assignment
11687 The assignment to an offset variable has the following syntax:
11690 @var{variable}=@var{value}
11694 where @var{variable} is the variable name, and @var{value} is a
11695 numeric value to be assigned to the variable.
11697 @item Boolean assignment
11699 To assign @code{true} value to a variable, simply put this variable name. To
11700 assign @code{false} value, prefix the variable name with @samp{no-}. For
11705 # Assign @code{true} value:
11707 # Assign @code{false} value:
11713 Following variables are declared:
11715 @deftypevr {Help Output} boolean dup-args
11716 If true, arguments for an option are shown with both short and long
11717 options, even when a given option has both forms, for example:
11720 -f ARCHIVE, --file=ARCHIVE use archive file or device ARCHIVE
11723 If false, then if an option has both short and long forms, the
11724 argument is only shown with the long one, for example:
11727 -f, --file=ARCHIVE use archive file or device ARCHIVE
11731 and a message indicating that the argument is applicable to both
11732 forms is printed below the options. This message can be disabled
11733 using @code{dup-args-note} (see below).
11735 The default is false.
11738 @deftypevr {Help Output} boolean dup-args-note
11739 If this variable is true, which is the default, the following notice
11740 is displayed at the end of the help output:
11743 Mandatory or optional arguments to long options are also mandatory or
11744 optional for any corresponding short options.
11747 Setting @code{no-dup-args-note} inhibits this message. Normally, only one of
11748 variables @code{dup-args} or @code{dup-args-note} should be set.
11751 @deftypevr {Help Output} offset short-opt-col
11752 Column in which short options start. Default is 2.
11756 $ @kbd{tar --help|grep ARCHIVE}
11757 -f, --file=ARCHIVE use archive file or device ARCHIVE
11758 $ @kbd{ARGP_HELP_FMT=short-opt-col=6 tar --help|grep ARCHIVE}
11759 -f, --file=ARCHIVE use archive file or device ARCHIVE
11764 @deftypevr {Help Output} offset long-opt-col
11765 Column in which long options start. Default is 6. For example:
11769 $ @kbd{tar --help|grep ARCHIVE}
11770 -f, --file=ARCHIVE use archive file or device ARCHIVE
11771 $ @kbd{ARGP_HELP_FMT=long-opt-col=16 tar --help|grep ARCHIVE}
11772 -f, --file=ARCHIVE use archive file or device ARCHIVE
11777 @deftypevr {Help Output} offset doc-opt-col
11778 Column in which @dfn{doc options} start. A doc option isn't actually
11779 an option, but rather an arbitrary piece of documentation that is
11780 displayed in much the same manner as the options. For example, in
11781 the description of @option{--format} option:
11785 -H, --format=FORMAT create archive of the given format.
11787 FORMAT is one of the following:
11789 gnu GNU tar 1.13.x format
11790 oldgnu GNU format as per tar <= 1.12
11791 pax POSIX 1003.1-2001 (pax) format
11793 ustar POSIX 1003.1-1988 (ustar) format
11794 v7 old V7 tar format
11799 the format names are doc options. Thus, if you set
11800 @kbd{ARGP_HELP_FMT=doc-opt-col=6} the above part of the help output
11801 will look as follows:
11805 -H, --format=FORMAT create archive of the given format.
11807 FORMAT is one of the following:
11809 gnu GNU tar 1.13.x format
11810 oldgnu GNU format as per tar <= 1.12
11811 pax POSIX 1003.1-2001 (pax) format
11813 ustar POSIX 1003.1-1988 (ustar) format
11814 v7 old V7 tar format
11819 @deftypevr {Help Output} offset opt-doc-col
11820 Column in which option description starts. Default is 29.
11824 $ @kbd{tar --help|grep ARCHIVE}
11825 -f, --file=ARCHIVE use archive file or device ARCHIVE
11826 $ @kbd{ARGP_HELP_FMT=opt-doc-col=19 tar --help|grep ARCHIVE}
11827 -f, --file=ARCHIVE use archive file or device ARCHIVE
11828 $ @kbd{ARGP_HELP_FMT=opt-doc-col=9 tar --help|grep ARCHIVE}
11830 use archive file or device ARCHIVE
11835 Notice, that the description starts on a separate line if
11836 @code{opt-doc-col} value is too small.
11839 @deftypevr {Help Output} offset header-col
11840 Column in which @dfn{group headers} are printed. A group header is a
11841 descriptive text preceding an option group. For example, in the
11845 Main operation mode:
11847 -A, --catenate, --concatenate append tar files to
11849 -c, --create create a new archive
11852 @samp{Main operation mode:} is the group header.
11854 The default value is 1.
11857 @deftypevr {Help Output} offset usage-indent
11858 Indentation of wrapped usage lines. Affects @option{--usage}
11859 output. Default is 12.
11862 @deftypevr {Help Output} offset rmargin
11863 Right margin of the text output. Used for wrapping.
11866 @node Fixing Snapshot Files
11867 @appendix Fixing Snapshot Files
11868 @include tar-snapshot-edit.texi
11870 @node Tar Internals
11871 @appendix Tar Internals
11872 @include intern.texi
11876 @include genfile.texi
11878 @node Free Software Needs Free Documentation
11879 @appendix Free Software Needs Free Documentation
11880 @include freemanuals.texi
11882 @node Copying This Manual
11883 @appendix Copying This Manual
11886 * GNU Free Documentation License:: License for copying this manual
11891 @node Index of Command Line Options
11892 @appendix Index of Command Line Options
11894 This appendix contains an index of all @GNUTAR{} long command line
11895 options. The options are listed without the preceding double-dash.
11896 For a cross-reference of short command line options, @ref{Short Option Summary}.
11909 @c Local variables:
11910 @c texinfo-column-for-description: 32