tar/doc/snapshot.texi

@c This is part of the paxutils manual.
@c Copyright (C) 2005 Free Software Foundation, Inc.
@c Written by Sergey Poznyakoff
@c This file is distributed under GFDL 1.1 or any later version
@c published by the Free Software Foundation.

  A @dfn{snapshot file} (or @dfn{directory file}) is created during
incremental backups (@pxref{Incremental Dumps}).  It
contains the status of the filesystem at the time of the dump and is
used to determine which files were modified since the last backup.

  @GNUTAR{} version @value{VERSION} supports two snapshot file
formats.  The first format, called @dfn{format 0}, is the one used by
@GNUTAR{} versions up to 1.15.1. The second format, called @dfn{format
1} is an extended version of this format, that contains more metadata
and allows for further extensions.

  @samp{Format 0} snapshot file begins with a line containing a
decimal number that represents the UNIX timestamp of the beginning of
the last archivation. This line is followed by directory metadata
descriptions, one per line. Each description has the following format:

@smallexample
[@var{nfs}]@var{dev} @var{inode} @var{name}
@end smallexample

@noindent
where optional @var{nfs} is a single plus character (@samp{+}) if this
directory is located on an NFS-mounted partition, @var{dev} and
@var{inode} are the device and inode numbers of the directory, and
@var{name} is the directory name.

  @samp{Format 1} snapshot file begins with a line specifying the
format of the file. This line has the following structure:

@smallexample
@samp{GNU tar-}@var{tar-version}@samp{-}@var{incr-format-version}
@end smallexample

@noindent
where @var{tar-version} is the version of @GNUTAR{} implementation
that created this snapshot, and @var{incr-format-version} is the
version number of the snapshot format (in this case @samp{1}).

  The following line contains two decimal numbers, representing the
time of the last backup. First number is the number of seconds, the
second one is the number of nanoseconds, since the beginning of the
epoch.

  Following lines contain directory metadate, one line per
directory. The line format is:

@smallexample
[@var{nfs}]@var{mtime-sec} @var{mtime-nsec} @var{dev} @var{inode} @var{name}
@end smallexample

@noindent
where @var{mtime-sec} and @var{mtime-nsec} represent the last
modification time of this directory with nanosecond precision;
@var{nfs}, @var{dev}, @var{inode} and @var{name} have the same meaning
as with @samp{format 0}.


@c End of snapshot.texi