File: tar.info,  Node: Incremental Dumps,  Next: Backup Levels,  Prev: Full Dumps,  Up: Backups

5.2 Using `tar' to Perform Incremental Dumps
============================================

"Incremental backup" is a special form of GNU `tar' archive that stores
additional metadata so that exact state of the file system can be
restored when extracting the archive.

   GNU `tar' currently offers two options for handling incremental
backups: `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') and
`--incremental' (`-G').

   The option `--listed-incremental' instructs tar to operate on an
incremental archive with additional metadata stored in a standalone
file, called a "snapshot file".  The purpose of this file is to help
determine which files have been changed, added or deleted since the
last backup, so that the next incremental backup will contain only
modified files.  The name of the snapshot file is given as an argument
to the option:

`--listed-incremental=FILE'
`-g FILE'
     Handle incremental backups with snapshot data in FILE.

   To create an incremental backup, you would use
`--listed-incremental' together with `--create' (*note create::).  For
example:

     $ tar --create \
                --file=archive.1.tar \
                --listed-incremental=/var/log/usr.snar \
                /usr

   This will create in `archive.1.tar' an incremental backup of the
`/usr' file system, storing additional metadata in the file
`/var/log/usr.snar'.  If this file does not exist, it will be created.
The created archive will then be a "level 0 backup"; please see the
next section for more on backup levels.

#! /bin/sh
# This program is part of GNU tar
# Copyright (C) 2004, 2006 Free Software Foundation, Inc.