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

   1 @c This is part of the paxutils manual.
   2 @c Copyright (C) 2005 Free Software Foundation, Inc.
   3 @c Written by Sergey Poznyakoff
   4 @c This file is distributed under GFDL 1.1 or any later version
   5 @c published by the Free Software Foundation.
   6
   7   A @dfn{snapshot file} (or @dfn{directory file}) is created during
   8 incremental backups (@pxref{Incremental Dumps}).  It
   9 contains the status of the filesystem at the time of the dump and is
  10 used to determine which files were modified since the last backup.
  11
  12   @GNUTAR{} version @value{VERSION} supports two snapshot file
  13 formats.  The first format, called @dfn{format 0}, is the one used by
  14 @GNUTAR{} versions up to 1.15.1. The second format, called @dfn{format
  15 1} is an extended version of this format, that contains more metadata
  16 and allows for further extensions.
  17
  18   @samp{Format 0} snapshot file begins with a line containing a
  19 decimal number that represents the UNIX timestamp of the beginning of
  20 the last archivation. This line is followed by directory metadata
  21 descriptions, one per line. Each description has the following format:
  22
  23 @smallexample
  24 [@var{nfs}]@var{dev} @var{inode} @var{name}
  25 @end smallexample
  26
  27 @noindent
  28 where optional @var{nfs} is a single plus character (@samp{+}) if this
  29 directory is located on an NFS-mounted partition, @var{dev} and
  30 @var{inode} are the device and inode numbers of the directory, and
  31 @var{name} is the directory name.
  32
  33   @samp{Format 1} snapshot file begins with a line specifying the
  34 format of the file. This line has the following structure:
  35
  36 @smallexample
  37 @samp{GNU tar-}@var{tar-version}@samp{-}@var{incr-format-version}
  38 @end smallexample
  39
  40 @noindent
  41 where @var{tar-version} is the version of @GNUTAR{} implementation
  42 that created this snapshot, and @var{incr-format-version} is the
  43 version number of the snapshot format (in this case @samp{1}).
  44
  45   The following line contains two decimal numbers, representing the
  46 time of the last backup. First number is the number of seconds, the
  47 second one is the number of nanoseconds, since the beginning of the
  48 epoch.
  49
  50   Following lines contain directory metadate, one line per
  51 directory. The line format is:
  52
  53 @smallexample
  54 [@var{nfs}]@var{mtime-sec} @var{mtime-nsec} @var{dev} @var{inode} @var{name}
  55 @end smallexample
  56
  57 @noindent
  58 where @var{mtime-sec} and @var{mtime-nsec} represent the last
  59 modification time of this directory with nanosecond precision;
  60 @var{nfs}, @var{dev}, @var{inode} and @var{name} have the same meaning
  61 as with @samp{format 0}.
  62
  63
  64 @c End of snapshot.texi
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