NAME

       rmt — remote magtape protocol module

SYNOPSIS

       rmt

DESCRIPTION

       Rmt  is  a  program  used  by  tar,  cpio, mt, and the remote dump and restore programs in manipulating a
       magnetic tape drive through an interprocess communication connection.  Rmt is normally started up with an
       rexec(3) or rcmd(3) call or the rsh(1) command.

       The rmt program accepts requests specific to the manipulation of magnetic tapes, performs  the  commands,
       then  responds with a status indication.  All responses are in ASCII and in one of two forms.  Successful
       commands have responses of:

             Anumber\n

       Number is an ASCII representation of a decimal number.  Unsuccessful commands are responded to with:

             Eerror-number\nerror-message\n

       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, which are sent as indicated - no spaces are supplied  between  the  command  and  its
       arguments, or between its arguments, and ‘\n’ indicates that a newline should be supplied:

       Odevice\nmode\n
               Open  the  specified  deviceusing  the  indicated  mode.Deviceis  a  full  pathname and modeis an
               ASCIIrepresentation 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.

       Cdevice\n
               Close the currently open device.  The devicespecified is ignored.

       Loffset\nwhence\n
               Perform  an  lseek(2)  operation  using  the  specified  parameters.   The response value is that
               returned from the lseek call.

       Wcount\n
               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.

       Rcount\n
               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 standard format
               is returned.  If the read was successful, the data read is then sent.

       Ioperation\ncount\n
               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.

DIAGNOSTICS

       All responses are of the form described above.

SEE ALSO

       tar(1), cpio(1), mt(1), rsh(1), rcmd(3), rexec(3), mtio(4), rdump(8), rrestore(8)

BUGS

       People should be discouraged from using this for a remote file access protocol.

HISTORY

       The rmt command appeared in 4.2BSD.

4.2 Berkeley Distribution                       December 11, 1993                                         RMT(8)