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RMT(8C)                                                                RMT(8C)

       rmt - remote magtape protocol module


       Rmt is a program used by the remote dump and restore programs in manip-
       ulating a magnetic tape drive  through  an  interprocess  communication
       connection.   Rmt  is normally started up with an rexec(3X) or rcmd(3X)

       The rmt program accepts requests specific to the manipulation  of  mag-
       netic tapes, performs the commands, then responds with a status indica-
       tion.  All responses are in ASCII and in one of two forms.   Successful
       commands have responses of


       where  number  is  an ASCII representation of a decimal number.  Unsuc-
       cessful commands are responded to with


       where error-number is one of the possible error  numbers  described  in
       intro(2) and error-message is the corresponding error string as printed
       from a call to perror(3).  The protocol is comprised of  the  following
       commands (a space is present between each token).

       O device mode  Open  the  specified  device  using  the indicated mode.
                      Device is a full pathname and mode is an ASCII represen-
                      tation  of  a  decimal  number  suitable  for passing to
                      open(2).  If a device had already  been  opened,  it  is
                      closed before a new open is performed.

       C device       Close  the  currently open device.  The device specified
                      is ignored.

       L whence offset
                      Perform an lseek(2) operation using the specified param-
                      eters.   The  response  value  is that returned from the
                      lseek call.

       W count        Write data onto the open device.  Rmt reads count  bytes
                      from the connection, aborting if a premature end-of-file
                      is encountered.  The response  value  is  that  returned
                      from the write(2) call.

       R count        Read count bytes of data from the open device.  If count
                      exceeds the size of the data buffer (10  kilobytes),  it
                      is truncated to the data buffer size.  Rmt then performs
                      the requested read(2) and responds with Acount-read\n if
                      the read was successful; otherwise an error in the stan-
                      dard format is returned.  If the  read  was  successful,
                      the data read is then sent.

       I operation count
                      Perform  a  MTIOCOP ioctl(2) command using the specified
                      parameters.  The parameters are interpreted as the ASCII
                      representations  of  the  decimal values to place in the
                      mt_op and mt_count fields of the structure used  in  the
                      ioctl  call.   The  return  value is the count parameter
                      when the operation is successful.

       S              Return the status of the open device, as obtained with a
                      MTIOCGET  ioctl  call.  If the operation was successful,
                      an ``ack'' is sent with the size of the  status  buffer,
                      then the status buffer is sent (in binary).

       Any other command causes rmt to exit.

       All responses are of the form described above.

       rcmd(3X), rexec(3X), mtio(4), rdump(8C), rrestore(8C)

       People  tempted  to use this for a remote file access protocol are dis-

4th Berkeley Distribution        4 March 1983                          RMT(8C)