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Archive format selection
-V name
--label=name
This option causes tar to write out a volume header at
the beginning of the archive. If `--multi-volume' (`-M') is used, each
volume of the archive will have a volume header of `name
Volume n', where n is 1 for the first volume, 2 for the
next, and so on.
-z
--gzip
--ungzip
gzip.
This option works on physical devices (tape drives, etc.) and remote
files as well as on normal files; data to or from such devices or
remote files is reblocked by another copy of the tar program
to enforce the specified (or default) block size. The default
compression parameters are used; if you need to override them, avoid
the `--gzip' (`-z') option and run gzip explicitly. (Or set the
`GZIP' environment variable.)
If the `--gzip' (`-z') option is given twice, or the
`--compress-blocks' option is used, tar will pad the archive
out to the next block boundary (
FIXME: pxref Blocking). This may be useful with some devices that require that all write operations be a multiple of a certain size.
The `--gzip' (`-z') option does not work with the `--multi-volume' (`-M') option, or with the `--update' (`-u'), `--append' (`-r'), `--concatenate' (`-A'), or `--delete' commands.
It is not exact to say that GNU tar is to work in concert
with gzip in a way similar to zip, say. Surely, it is
possible that tar and gzip be done with a single call,
like in:
tar cfz archive.tar.gz subdir
to save all of `subdir' into a gzip'ed archive. Later you
can do:
tar xfz archive.tar.gz
to explode and unpack.
The difference is that the whole archive is compressed. With
zip, archive members are archived individually. tar's
method yields better compression. On the other hand, one can view the
contents of a zip archive without having to decompress it. As
for the tar and gzip tandem, you need to decompress the
archive to see its contents. However, this may be done without needing
disk space, by using pipes internally:
tar tfz archive.tar.gz
About corrupted compressed archives: gzip'ed files have no
redundancy, for maximum compression. The adaptive nature of the
compression scheme means that the compression tables are implicitly
spread all over the archive. If you lose a few blocks, the dynamic
construction of the compression tables becomes unsychronized, and there
is little chance that you could recover later in the archive.
There are pending suggestions for having a per-volume or per-file
compression in GNU tar. This would allow for viewing the
contents without decompression, and for resynchronizing decompression at
every volume or file, in case of corrupted archives. Doing so, we might
loose some compressibility. But this would have make recovering easier.
So, there are pros and cons. We'll see!
-Z
--compress
--uncompress
compress. Otherwise like `--gzip' (`-z').
--use-compress-program=prog
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