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Making backups with tar

A full backup can easily be made with tar :

# tar -create -file /dev/ftape /usr/src
tar: Removing leading / from absolute path names in the archive
#

The example above uses the GNU version of tar  and its long option names. The traditional version of tar  only understands single character options. The GNU version can also handle backups that don't fit on one tape or floppy, and also very long paths; not all traditional versions can do these things. (Linux only uses GNU tar .)

If your backup doesn't fit on one tape, you need to use the -multi-volume (-M) option:

# tar -cMf /dev/fd0H1440 /usr/src
tar: Removing leading / from absolute path names in the archive
Prepare volume #2 for /dev/fd0H1440 and hit return:
#

Note that you should format the floppies before you begin the backup, or else use another window or virtual terminal and do it when tar  asks for a new floppy.

After you've made a backup, you should check that it is OK, using the -compare (-d) option:

# tar -compare -verbose -f /dev/ftape
usr/src/
usr/src/linux
usr/src/linux-1.2.10-includes/
....
#

Failing to check a backup means that you will not notice that your backups aren't working until after you've lost the original data.

An incremental backup can be done with tar  using the -newer (-N) option:

# tar -create -newer '8 Sep 1995' -file /dev/ftape /usr/src -verbose
tar: Removing leading / from absolute path names in the archive
usr/src/
usr/src/linux-1.2.10-includes/
usr/src/linux-1.2.10-includes/include/
usr/src/linux-1.2.10-includes/include/linux/
usr/src/linux-1.2.10-includes/include/linux/modules/
usr/src/linux-1.2.10-includes/include/asm-generic/
usr/src/linux-1.2.10-includes/include/asm-i386/
usr/src/linux-1.2.10-includes/include/asm-mips/
usr/src/linux-1.2.10-includes/include/asm-alpha/
usr/src/linux-1.2.10-includes/include/asm-m68k/
usr/src/linux-1.2.10-includes/include/asm-sparc/
usr/src/patch-1.2.11.gz
#

Unfortunately, tar  can't notice when a file's inode information has changed, for example, that it's permission bits have been changed, or when its name has been changed. This can be worked around using find  and comparing current filesystem state with lists of files that have been previously backed up. Scripts and programs for doing this can be found on Linux ftp sites.