X-Git-Url: https://git.dogcows.com/gitweb?p=chaz%2Ftar;a=blobdiff_plain;f=doc%2Ftar-snapshot-edit.texi;h=9dc96f54b4c7612e7e2f842446c2eeb44aae54bc;hp=9c930efe3c8ef493329ee845c54d6d6273941603;hb=45ccda119355a1087450039a250359c1d0de0d08;hpb=338add8d10a787aafb6fd57aeae497a79a8d5855

diff --git a/doc/tar-snapshot-edit.texi b/doc/tar-snapshot-edit.texi
index 9c930ef..9dc96f5 100644
--- a/doc/tar-snapshot-edit.texi
+++ b/doc/tar-snapshot-edit.texi
@@ -1,29 +1,33 @@
 @c This is part of the paxutils manual.
-@c Copyright (C) 2007 Free Software Foundation, Inc.
+@c Copyright (C) 2007, 2014 Free Software Foundation, Inc.
 @c This file is distributed under GFDL 1.1 or any later version
 @c published by the Free Software Foundation.
 
 @cindex Device numbers, changing
 @cindex snapshot files, editing
 @cindex snapshot files, fixing device numbers
-  Sometimes device numbers can change after upgrading your kernel
-version or reconfiguring the hardware.  Reportedly this is the case with
-some newer @i{Linux} kernels, when using @acronym{LVM}.  In majority of
+  Various situations can cause device numbers to change: upgrading your
+kernel version, reconfiguring your hardware, loading kernel modules in a
+different order, using virtual volumes that are assembled dynamically
+(such as with @acronym{LVM} or @acronym{RAID}), hot-plugging drives
+(e.g. external USB or Firewire drives), etc.  In the majority of 
 cases this change is unnoticed by the users.  However, it influences
 @command{tar} incremental backups: the device number is stored in tar
 snapshot files (@pxref{Snapshot Files}) and is used to determine whether
 the file has changed since the last backup.  If the device numbers
-change for some reason, the next backup you run will be a full backup.
+change for some reason, by default the next backup you run will be a
+full backup.
+
 
 @pindex tar-snapshot-edit
   To minimize the impact in these cases, GNU @command{tar} comes with
 the @command{tar-snapshot-edit} utility for inspecting and updating
-device numbers in snapshot files.  The utility, written by
-Dustin J.@: Mitchell, is available from
+device numbers in snapshot files.  (The utility, written by
+Dustin J.@: Mitchell, is also available from the
 @uref{http://www.gnu.org/@/software/@/tar/@/utils/@/tar-snapshot-edit.html,
-@GNUTAR{} home page}.
+@GNUTAR{} home page}.)
 
-  To obtain the device numbers used in the snapshot file, run
+  To obtain a summary of the device numbers found in the snapshot file, run
 
 @smallexample
 $ @kbd{tar-snapshot-edit @var{snapfile}}
@@ -31,10 +35,19 @@ $ @kbd{tar-snapshot-edit @var{snapfile}}
 
 @noindent
 where @var{snapfile} is the name of the snapshot file (you can supply as many
-files as you wish in a single command line).
+files as you wish in a single command line).  You can then compare the 
+numbers across snapshot files, or against those currently in use on the
+live filesystem (using @command{ls -l} or @command{stat}).
+
+  Assuming the device numbers have indeed changed, it's often possible
+to simply tell @GNUTAR{} to ignore the device number when processing the
+incremental snapshot files for these backups, using the
+@option{--no-check-device} option (@pxref{device numbers}).
 
-To update all occurrences of the given device number in the file, use
-@option{-r} option.  It takes a single argument of the form
+  Alternatively, you can use the @command{tar-edit-snapshot} script's 
+@option{-r} option to update all occurrences of the given device
+number in the snapshot file(s).  It takes a single argument
+of the form
 @samp{@var{olddev}-@var{newdev}},  where @var{olddev} is the device number
 used in the snapshot file, and @var{newdev} is the corresponding new device
 number.  Both numbers may be specified in hex (e.g., @samp{0xfe01}),
@@ -49,10 +62,30 @@ backup file is obtained by appending @samp{~} to the original file name.
 
 An example session:
 @smallexample
-$ @kbd{tar-snapshot-edit /var/backup/snap.a}
-file version 2
-/tmp/snap: Device 0x0306 occurs 634 times.
-$ @kbd{tar-snapshot-edit -b -r 0x0306-0x4500 /var/backup/snap.a}
-file version 2
-@end smallexample
+$ @kbd{tar-snapshot-edit root_snap.0 boot_snap.0}
+File: root_snap.0
+  Detected snapshot file version: 2
+
+  Device 0x0000 occurs 1 times.
+  Device 0x0003 occurs 1 times.
+  Device 0x0005 occurs 1 times.
+  Device 0x0013 occurs 1 times.
+  Device 0x6801 occurs 1 times.
+  Device 0x6803 occurs 6626 times.
+  Device 0xfb00 occurs 1 times.
+
+File: boot_snap.0
+  Detected snapshot file version: 2
 
+  Device 0x6801 occurs 3 times.
+$ @kbd{tar-snapshot-edit -b -r 0x6801-0x6901,0x6803-0x6903 root_snap.0 boot_snap.0}
+File: root_snap.0
+  Detected snapshot file version: 2
+
+  Updated 6627 records.
+
+File: boot_snap.0
+  Detected snapshot file version: 2
+
+  Updated 3 records.
+@end smallexample