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(tar.info)Full Dumps

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Using `tar' to Perform Full Dumps
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   Full dumps should only be made when no other people or programs are
modifying files in the filesystem.  If files are modified while `tar'
is making the backup, they may not be stored properly in the archive,
in which case you won't be able to restore them if you have to.  (Files
not being modified are written with no trouble, and do not corrupt the
entire archive.)

   You will want to use the `--label=ARCHIVE-LABEL' (`-V
ARCHIVE-LABEL') option to give the archive a volume label, so you can
tell what this archive is even if the label falls off the tape, or
anything like that.

   Unless the filesystem you are dumping is guaranteed to fit on one
volume, you will need to use the `--multi-volume' (`-M') option.  Make
sure you have enough tapes on hand to complete the backup.

   If you want to dump each filesystem separately you will need to use
the `--one-file-system' (`-l') option to prevent `tar' from crossing
filesystem boundaries when storing (sub)directories.

   The `--incremental' (`-G') option is not needed, since this is a
complete copy of everything in the filesystem, and a full restore from
this backup would only be done onto a completely empty disk.

   Unless you are in a hurry, and trust the `tar' program (and your
tapes), it is a good idea to use the `--verify' (`-W') option, to make
sure your files really made it onto the dump properly.  This will also
detect cases where the file was modified while (or just after) it was
being archived.  Not all media (notably cartridge tapes) are capable of
being verified, unfortunately.

   `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') take a
file name argument always.  If the file doesn't exist, run a level zero
dump, creating the file.  If the file exists, uses that file to see
what has changed.

   `--incremental' (`-G')

   `--incremental' (`-G') handle old GNU-format incremental backup.

   This option should only be used when creating an incremental backup
of a filesystem.  When the `--incremental' (`-G') option is used, `tar'
writes, at the beginning of the archive, an entry for each of the
directories that will be operated on.  The entry for a directory
includes a list of all the files in the directory at the time the dump
was done, and a flag for each file indicating whether the file is going
to be put in the archive.  This information is used when doing a
complete incremental restore.

   Note that this option causes `tar' to create a non-standard archive
that may not be readable by non-GNU versions of the `tar' program.

   The `--incremental' (`-G') option means the archive is an incremental
backup.  Its meaning depends on the command that it modifies.

   If the `--incremental' (`-G') option is used with `--list' (`-t'),
`tar' will list, for each directory in the archive, the list of files in
that directory at the time the archive was created.  This information
is put out in a format that is not easy for humans to read, but which
is unambiguous for a program: each file name is preceded by either a
`Y' if the file is present in the archive, an `N' if the file is not
included in the archive, or a `D' if the file is a directory (and is
included in the archive).  Each file name is terminated by a null
character.  The last file is followed by an additional null and a
newline to indicate the end of the data.

   If the `--incremental' (`-G') option is used with `--extract'
(`--get', `-x'), then when the entry for a directory is found, all
files that currently exist in that directory but are not listed in the
archive _are deleted from the directory_.

   This behavior is convenient when you are restoring a damaged file
system from a succession of incremental backups: it restores the entire
state of the file system to that which obtained when the backup was
made.  If you don't use `--incremental' (`-G'), the file system will
probably fill up with files that shouldn't exist any more.

   `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') handle new
GNU-format incremental backup.  This option handles new GNU-format
incremental backup.  It has much the same effect as `--incremental'
(`-G'), but also the time when the dump is done and the list of
directories dumped is written to the given FILE. When restoring, only
files newer than the saved time are restored, and the directory list is
used to speed up operations.

   `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') acts like
`--incremental' (`-G'), but when used in conjunction with `--create'
(`-c') will also cause `tar' to use the file FILE, which contains
information about the state of the filesystem at the time of the last
backup, to decide which files to include in the archive being created.
That file will then be updated by `tar'.  If the file FILE does not
exist when this option is specified, `tar' will create it, and include
all appropriate files in the archive.

   The file, which is archive independent, contains the date it was last
modified and a list of devices, inode numbers and directory names.
`tar' will archive files with newer mod dates or inode change times,
and directories with an unchanged inode number and device but a changed
directory name.  The file is updated after the files to be archived are
determined, but before the new archive is actually created.

   GNU `tar' actually writes the file twice: once before the data and
written, and once after.