Dogcows Code - chaz/tar/blob - doc/tar-snapshot-edit.texi

   1 @c This is part of the paxutils manual.
   2 @c Copyright (C) 2007 Free Software Foundation, Inc.
   3 @c This file is distributed under GFDL 1.1 or any later version
   4 @c published by the Free Software Foundation.
   5
   6 @cindex Device numbers, changing
   7 @cindex snapshot files, editing
   8 @cindex snapshot files, fixing device numbers
   9   Sometimes device numbers can change after upgrading your kernel
  10 version or recofiguring the harvare.  Reportedly this is the case with
  11 some newer @i{Linux} kernels, when using @acronym{LVM}.  In majority of
  12 cases this change is unnoticed by the users.  However, it influences
  13 @command{tar} incremental backups: the device number is stored in tar
  14 snapshot files (@pxref{Snapshot Files}) and is used to determine whether
  15 the file has changed since the last backup.  If the device numbers
  16 change for some reason, the next backup you run will be a full backup.
  17
  18 @pindex tar-snapshot-edit
  19   To minimize the impact in these cases, GNU @command{tar} comes with
  20 the @command{tar-snapshot-edit} utility for inspecting and updating
  21 device numbers in snapshot files.  The utility, written by
  22 Dustin J.@: Mitchell, is available from
  23 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tar-snapshot-edit.html,
  24 @GNUTAR{} home page}.
  25
  26   To obtain the device numbers used in the snapshot file, run
  27
  28 @smallexample
  29 $ @kbd{tar-snapshot-edit @var{snapfile}}
  30 @end smallexample
  31
  32 @noindent
  33 where @var{snapfile} is the name of the snapshot file (you can supply as many
  34 files as you wish in a single command line ).
  35
  36 To update all occurrences of the given device number in the file, use
  37 @option{-r} option.  It takes a single argument of the form
  38 @samp{@var{olddev}-@var{newdev}},  where @var{olddev} is the device number
  39 used in the snapshot file, and @var{newdev} is the corresponding new device
  40 number.  Both numbers may be specified in hex (e.g., @samp{0xfe01}),
  41 decimal (e.g., @samp{65025}), or as a major:minor number pair (e.g.,
  42 @samp{254:1}).  To change several device numbers at once, specify them
  43 in a single comma-separated list, as in
  44 @option{-r 0x3060-0x4500,0x307-0x4600}.
  45
  46 Before updating the snapshot file, it is a good idea to create a backup
  47 copy of it.  This is accomplished by @samp{-b} option.  The name of the
  48 backup file is obtained by appending @samp{~} to the original file name.
  49
  50 An example session:
  51 @smallexample
  52 $ @kbd{tar-snapshot-edit /var/backup/snap.a}
  53 file version 2
  54 /tmp/snap: Device 0x0306 occurs 634 times.
  55 $ @kbd{tar-snapshot-edit -b -r 0x0306-0x4500 /var/backup/snap.a}
  56 file version 2
  57 @end smallexample
  58