tar: Device
1
1 9.1 Device Selection and Switching
1 ==================================
1
1 _(This message will disappear, once this node revised.)_
1
1 '-f [HOSTNAME:]FILE'
1 '--file=[HOSTNAME:]FILE'
1 Use archive file or device FILE on HOSTNAME.
1
1 This option is used to specify the file name of the archive 'tar'
1 works on.
1
1 If the file name is '-', 'tar' reads the archive from standard input
1 (when listing or extracting), or writes it to standard output (when
1 creating). If the '-' file name is given when updating an archive,
1 'tar' will read the original archive from its standard input, and will
1 write the entire new archive to its standard output.
1
1 If the file name contains a ':', it is interpreted as 'hostname:file
1 name'. If the HOSTNAME contains an "at" sign ('@'), it is treated as
1 'user@hostname:file name'. In either case, 'tar' will invoke the
1 command 'rsh' (or 'remsh') to start up an '/usr/libexec/rmt' on the
1 remote machine. If you give an alternate login name, it will be given
1 to the 'rsh'. Naturally, the remote machine must have an executable
1 '/usr/libexec/rmt'. This program is free software from the University
1 of California, and a copy of the source code can be found with the
1 sources for 'tar'; it's compiled and installed by default. The exact
1 path to this utility is determined when configuring the package. It is
1 'PREFIX/libexec/rmt', where PREFIX stands for your installation prefix.
1 This location may also be overridden at runtime by using the
1 '--rmt-command=COMMAND' option (⇒--rmt-command Option Summary, for
1 detailed description of this option. ⇒Remote Tape Server, for
1 the description of 'rmt' command).
1
1 If this option is not given, but the environment variable 'TAPE' is
1 set, its value is used; otherwise, old versions of 'tar' used a default
1 archive name (which was picked when 'tar' was compiled). The default is
1 normally set up to be the "first" tape drive or other transportable I/O
1 medium on the system.
1
1 Starting with version 1.11.5, GNU 'tar' uses standard input and
1 standard output as the default device, and I will not try anymore
1 supporting automatic device detection at installation time. This was
1 failing really in too many cases, it was hopeless. This is now
1 completely left to the installer to override standard input and standard
1 output for default device, if this seems preferable. Further, I think
1 _most_ actual usages of 'tar' are done with pipes or disks, not really
1 tapes, cartridges or diskettes.
1
1 Some users think that using standard input and output is running
1 after trouble. This could lead to a nasty surprise on your screen if
1 you forget to specify an output file name--especially if you are going
1 through a network or terminal server capable of buffering large amounts
1 of output. We had so many bug reports in that area of configuring
1 default tapes automatically, and so many contradicting requests, that we
1 finally consider the problem to be portably intractable. We could of
1 course use something like '/dev/tape' as a default, but this is _also_
1 running after various kind of trouble, going from hung processes to
1 accidental destruction of real tapes. After having seen all this mess,
1 using standard input and output as a default really sounds like the only
1 clean choice left, and a very useful one too.
1
1 GNU 'tar' reads and writes archive in records, I suspect this is the
1 main reason why block devices are preferred over character devices.
1 Most probably, block devices are more efficient too. The installer
1 could also check for 'DEFTAPE' in '<sys/mtio.h>'.
1
1 '--force-local'
1 Archive file is local even if it contains a colon.
1
1 '--rsh-command=COMMAND'
1 Use remote COMMAND instead of 'rsh'. This option exists so that
1 people who use something other than the standard 'rsh' (e.g., a
1 Kerberized 'rsh') can access a remote device.
1
1 When this command is not used, the shell command found when the
1 'tar' program was installed is used instead. This is the first
1 found of '/usr/ucb/rsh', '/usr/bin/remsh', '/usr/bin/rsh',
1 '/usr/bsd/rsh' or '/usr/bin/nsh'. The installer may have
1 overridden this by defining the environment variable 'RSH' _at
1 installation time_.
1
1 '-[0-7][lmh]'
1 Specify drive and density.
1
1 '-M'
1 '--multi-volume'
1 Create/list/extract multi-volume archive.
1
1 This option causes 'tar' to write a "multi-volume" archive--one
1 that may be larger than will fit on the medium used to hold it.
1 ⇒Multi-Volume Archives.
1
1 '-L NUM'
1 '--tape-length=SIZE[SUF]'
1 Change tape after writing SIZE units of data. Unless SUF is given,
1 SIZE is treated as kilobytes, i.e. 'SIZE x 1024' bytes. The
1 following suffixes alter this behavior:
1
1 Suffix Units Byte Equivalent
1 -------------------------------------------------------------
1 b Blocks SIZE x 512
1 B Kilobytes SIZE x 1024
1 c Bytes SIZE
1 G Gigabytes SIZE x 1024^3
1 K Kilobytes SIZE x 1024
1 k Kilobytes SIZE x 1024
1 M Megabytes SIZE x 1024^2
1 P Petabytes SIZE x 1024^5
1 T Terabytes SIZE x 1024^4
1 w Words SIZE x 2
1
1 Table 9.1: Size Suffixes
1
1 This option might be useful when your tape drivers do not properly
1 detect end of physical tapes. By being slightly conservative on
1 the maximum tape length, you might avoid the problem entirely.
1
1 '-F COMMAND'
1 '--info-script=COMMAND'
1 '--new-volume-script=COMMAND'
1 Execute COMMAND at end of each tape. This implies '--multi-volume'
1 ('-M'). ⇒info-script, for a detailed description of this
1 option.
1