(tar.info.gz) Device

Info Catalog (tar.info.gz) Media (tar.info.gz) Remote Tape Server
 
 9.1 Device Selection and Switching
 ==================================
 
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 '-f [HOSTNAME:]FILE'
 '--file=[HOSTNAME:]FILE'
      Use archive file or device FILE on HOSTNAME.
 
    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 the
 '--rmt-command=COMMAND' option ( --rmt-command Option Summary, for
 detailed description of this option.   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 'RSH' _at
      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.
       Multi-Volume Archives.
 
 '-L NUM'
 '--tape-length=SIZE[SUF]'
      Change tape after writing SIZE units of data.  Unless SUF is given,
      SIZE is treated as kilobytes, i.e.  'SIZE x 1024' bytes.  The
      following suffixes alter this behavior:
 
      Suffix         Units                  Byte Equivalent
      -------------------------------------------------------------
      b              Blocks                 SIZE x 512
      B              Kilobytes              SIZE x 1024
      c              Bytes                  SIZE
      G              Gigabytes              SIZE x 1024^3
      K              Kilobytes              SIZE x 1024
      k              Kilobytes              SIZE x 1024
      M              Megabytes              SIZE x 1024^2
      P              Petabytes              SIZE x 1024^5
      T              Terabytes              SIZE x 1024^4
      w              Words                  SIZE x 2
 
      Table 9.1: Size Suffixes
 
      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').   info-script, for a detailed description of this
      option.
 
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