This option is used to specify the file name of the archive tar
works on.
If the file name is ‘-’, tar reads the archive from standard
input (when listing or extracting), or writes it to standard output
(when creating). If the ‘-’ file name is given when updating an
archive, tar will read the original archive from its standard
input, and will write the entire new archive to its standard output.
If the file name contains a ‘:’, it is interpreted as
‘hostname:file name’. If the hostname contains an at
sign (‘@’), it is treated as ‘user@hostname:file name’. In
either case, tar will invoke the command rsh (or
remsh) to start up an /usr/libexec/rmt on the remote
machine. If you give an alternate login name, it will be given to the
rsh.
Naturally, the remote machine must have an executable
/usr/libexec/rmt. This program is free software from the
University of California, and a copy of the source code can be found
with the sources for tar; it's compiled and installed by default.
The exact path to this utility is determined when configuring the package.
It is prefix/libexec/rmt, where prefix stands for
your installation prefix. This location may also be overridden at
runtime by using rmt-command=command option (See —rmt-command, for detailed description of this option. See Remote Tape Server, for the description of rmt command).
If this option is not given, but the environment variable TAPE
is set, its value is used; otherwise, old versions of tar
used a default archive name (which was picked when tar was
compiled). The default is normally set up to be the first tape
drive or other transportable I/O medium on the system.
Starting with version 1.11.5, GNU tar uses
standard input and standard output as the default device, and I will
not try anymore supporting automatic device detection at installation
time. This was failing really in too many cases, it was hopeless.
This is now completely left to the installer to override standard
input and standard output for default device, if this seems
preferable. Further, I think most actual usages of
tar are done with pipes or disks, not really tapes,
cartridges or diskettes.
Some users think that using standard input and output is running
after trouble. This could lead to a nasty surprise on your screen if
you forget to specify an output file name—especially if you are going
through a network or terminal server capable of buffering large amounts
of output. We had so many bug reports in that area of configuring
default tapes automatically, and so many contradicting requests, that
we finally consider the problem to be portably intractable. We could
of course use something like ‘/dev/tape’ as a default, but this
is also running after various kind of trouble, going from hung
processes to accidental destruction of real tapes. After having seen
all this mess, using standard input and output as a default really
sounds like the only clean choice left, and a very useful one too.
GNU tar reads and writes archive in records, I
suspect this is the main reason why block devices are preferred over
character devices. Most probably, block devices are more efficient
too. The installer could also check for ‘DEFTAPE’ in
<sys/mtio.h>.
--force-local
Archive file is local even if it contains a colon.
--rsh-command=command
Use remote command instead of rsh. This option exists
so that people who use something other than the standard rsh
(e.g., a Kerberized rsh) can access a remote device.
When this command is not used, the shell command found when
the tar program was installed is used instead. This is
the first found of /usr/ucb/rsh, /usr/bin/remsh,
/usr/bin/rsh, /usr/bsd/rsh or /usr/bin/nsh.
The installer may have overridden this by defining the environment
variable RSHat installation time.
-[0-7][lmh]
Specify drive and density.
-M
--multi-volume
Create/list/extract multi-volume archive.
This option causes tar to write a multi-volume archive—one
that may be larger than will fit on the medium used to hold it.
See Multi-Volume Archives.
-L num
--tape-length=num
Change tape after writing num x 1024 bytes.
This option might be useful when your tape drivers do not properly
detect end of physical tapes. By being slightly conservative on the
maximum tape length, you might avoid the problem entirely.
-F file
--info-script=file
--new-volume-script=file
Execute file at end of each tape. This implies
--multi-volume (-M). See info-script, for a detailed
description of this option.
Published under the terms of the GNU General Public License
