RMT(8)                  (March 24, 2018)                   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 charac-
          ter.  Additional data, if any, are sent after the newline.
          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.:

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                        576
                        64|512
                        CREAT|TRUNC
                    In addition, a combined form is also allowed, i.e.
                    a decimal mode followed by its symbolic represen-
                    tation.  In this case the symbolic representation
                    is given preference.

               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 specified 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.

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               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 num-
                    ber 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 discouraged.

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     BUG REPORTS
          Report bugs to <bug-tar@gnu.org>.

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

     COPYRIGHT
          Copyright c 2013, 2018 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  redis-
          tribute  it.   There is NO WARRANTY, to the extent permitted
          by law.

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