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RMT(8)                          GNU TAR Manual                          RMT(8)



NAME
       rmt - remote magnetic tape server

SYNOPSIS
       rmt

DESCRIPTION
       Rmt  provides  remote  access to files and devices for tar(1), cpio(1),
       and similar backup utilities.  It is normally called by running  rsh(1)
       or  ssh(1)  to  the  remote machine, optionally using a different login
       name if one is supplied.

       The calling program communicates with rmt by sending  requests  on  its
       standard input and reading replies from the standard output.  A request
       consists of a request letter followed by an argument (if required)  and
       a  newline character.  Additional data, if any, are sent after the new-
       line.  On success, rmt returns

           Anumber\n

       where number is an ASCII  representation  of  a  decimal  return  code.
       Additional  data are returned after this line.  On error, the following
       response is returned:

           Eerrno\nerror-message\n

       where errno is one of the system error codes, as described in errno(3),
       and  error-message  is  a  one-line  human-readable  description of the
       error, as printed by perror(3).

       Available commands and possible responses are discussed  in  detail  in
       the subsequent section.

COMMANDS
       Odevice\nflags\n
              Opens  the device with given flags. If a device had already been
              opened, it is closed before opening the new one.

              Arguments

              device The name of the device to open.

              flags  Flags for open(2): a decimal number,  or  any  valid  O_*
                     constant from fcntl.h (the initial O_ may be omitted), or
                     a bitwise or (using |) of any number of these, e.g.:
                         576
                         64|512
                         CREAT|TRUNC
                     In addition, a combined form is also allowed, i.e. a dec-
                     imal  mode  followed  by its symbolic representation.  In
                     this case the symbolic representation  is  given  prefer-
                     ence.

              Reply
                     A0\n on success.

              Extensions
                     BSD version allows only decimal number as flags.

       C[device]\n
              Close the currently open device.

              Arguments
                     Any arguments are silently ignored.

              Reply
                     A0\n on success.

       Lwhence\noffset\n
              Performs an lseek(2) on the currently open device with the spec-
              ified parameters.

              Arguments

                     whence Where to measure offset from. Valid values are:

                             0, SET, SEEK_SET   seek from the file beginning
                             1, CUR, SEEK_CUR   seek from the current location
                             2, END, SEEK_END   seek from the file end

              Reply
                     Aoffset\n on success. The offset is  the  new  offset  in
                     file.

              Extensions
                     BSD version allows only 0,1,2 as whence.

       Rcount\n
              Read count bytes of data from the current device.

              Arguments

                     count  number of bytes to read.

              Reply
                     On success:

                         Ardcount\n

                     followed by rdcount bytes of data read from the device.

       Wcount\n
              Writes data onto the current device.  The command is followed by
              count bytes of input data.

              Arguments

                     count  Number of bytes to write.

              Reply
                     On success: Awrcount\n, where wrcount is  the  number  of
                     bytes actually written.

       Iopcode\ncount\n
              Perform   a   MTIOCOP   ioctl(2)   command  with  the  specified
              paramedters.

              Arguments

                     opcode MTIOCOP operation code.

                     count  mt_count.

              Reply
                     On success: A0\n.

       S\n    Returns the status of the currently  open  device,  as  obtained
              from a MTIOCGET ioctl(2) call.

              Arguments
                     None

              Reply
                     On success: Acount\n followed by count bytes of data.

SEE ALSO
       tar(1).

BUGS
       Using this utility as a general-purpose remote file access tool is dis-
       couraged.

BUG REPORTS
       Report bugs to <bug-tarATgnu.org>.

HISTORY
       The rmt command appeared in  4.2BSD.   The  GNU  rmt  is  written  from
       scratch, using the BSD specification.

COPYRIGHT
       Copyright (C) 2013 Free Software Foundation, Inc.
       License GPLv3+: GNU GPL version 3 or later
       <http://gnu.org/licenses/gpl.html>;
       This is free software: you are free  to  change  and  redistribute  it.
       There is NO WARRANTY, to the extent permitted by law.



RMT                            January 27, 2014                         RMT(8)