(tar.info.gz) Snapshot Files

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 Format of the Incremental Snapshot Files
 ========================================
 
 A "snapshot file" (or "directory file") is created during incremental
 backups ( Incremental Dumps).  It contains the status of the file
 system at the time of the dump and is used to determine which files were
 modified since the last backup.
 
    GNU 'tar' version 1.26 supports three snapshot file formats.  The
 first format, called "format 0", is the one used by GNU 'tar' versions
 up to 1.15.1.  The second format, called "format 1" is an extended
 version of this format, that contains more metadata and allows for
 further extensions.  It was used by version 1.15.1.  Starting from
 version 1.16 and up to 1.26, the "format 2" is used.
 
    GNU 'tar' is able to read all three formats, but will create
 snapshots only in format 2.
 
    This appendix describes all three formats in detail.
 
   0. 'Format 0' snapshot file begins with a line containing a decimal
      number that represents a 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:
 
           NFSDEV INODE NAME
 
      where:
 
      NFS
           A single plus character ('+'), if this directory is located on
           an NFS-mounted partition, or a single space otherwise;
 
      DEV
           Device number of the directory;
 
      INODE
           I-node number of the directory;
 
      NAME
           Name of the directory.  Any special characters (white-space,
           backslashes, etc.)  are quoted.
 
   1. 'Format 1' snapshot file begins with a line specifying the format
      of the file.  This line has the following structure:
 
           'GNU tar-'TAR-VERSION'-'INCR-FORMAT-VERSION
 
      where TAR-VERSION is the version number of GNU 'tar' implementation
      that created this snapshot, and INCR-FORMAT-VERSION is the version
      number of the snapshot format (in this case '1').
 
      Next 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.
 
      Lines that follow contain directory metadata, one line per
      directory.  Each line is formatted as follows:
 
           [NFS]MTIME-SEC MTIME-NSEC DEV INODE NAME
 
      where MTIME-SEC and MTIME-NSEC represent last modification time of
      this directory with nanosecond precision; NFS, DEV, INODE and NAME
      have the same meaning as with 'format 0'.
 
   2. 'Format 2' snapshot file begins with a format identifier, as
      described for version 1, e.g.:
 
           GNU tar-1.26-2
 
      This line is followed by newline.  Rest of file consists of
      records, separated by null (ASCII 0) characters.  Thus, in contrast
      to the previous formats, format 2 snapshot is a binary file.
 
      First two records are 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.
      These are followed by arbitrary number of directory records.
 
      Each "directory record" contains a set of metadata describing a
      particular directory.  Parts of a directory record are delimited
      with ASCII 0 characters.  The following table describes each part.
      The "Number" type in this table stands for a decimal number in
      ASCII notation.
 
      Field          Type           Description
      --------------------------------------------------------------------------
      nfs            Character      '1' if the directory is located on an
                                    NFS-mounted partition, or '0' otherwise;
      mtime-sec      Number         Modification time, seconds;
      mtime-nano     Number         Modification time, nanoseconds;
      dev-no         Number         Device number;
      i-no           Number         I-node number;
      name           String         Directory name; in contrast to the
                                    previous versions it is not quoted;
      contents       Dumpdir        Contents of the directory; 
                                    Dumpdir, for a description of its
                                    format.
 
      Dumpdirs stored in snapshot files contain only records of types
      'Y', 'N' and 'D'.
 
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