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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(3N) or rcmd(3N)

       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

              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

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

                             Perform a  MTIOCOP  ioctl(2)  command  using  the
                             specified  parameters.  The parameters are inter-
                             preted as the ASCII representations of the  deci-
                             mal  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.

                             Perform an lseek(2V) operation using  the  speci-
                             fied  parameters.   The  response  value  is that
                             returned from the lseek call.

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

              Rcount         Read  count  bytes  of data from the open device.
                             rmt performs the requested read(2V) and  responds
                             with  Acount-read\n  if  the read was successful;
                             otherwise an error  in  the  standard  format  is
                             returned.   If  the read was successful, the data
                             read is then sent.

              Wcount         Write data onto the open device.  rmt reads count
                             bytes  from  the connection, aborting if a prema-
                             ture EOF is encountered.  The response  value  is
                             that returned from the write(2V) call.

       Any other command causes rmt to exit.

       All responses are of the form described above.

       intro(2),  ioctl(2),  lseek(2V),  open(2V),  read(2V),  write(2V), per-
       ror(3), rcmd(3N), rexec(3N), mtio(4), dump(8), restore(8)

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

                                  26 May 1988                          RMT(8C)