RMT(8)                                             System management commands                                             RMT(8)



NAME
       rmt - remote magtape protocol module

SYNOPSIS
       rmt

DESCRIPTION
       Rmt  is a program used by the remote dump(8), restore(8) or tar(1) 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.

       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 the following two forms.

       Successful commands have responses of:
              Anumber\n

       where number is an ASCII representation of a decimal number.

       Unsuccessful commands are responded to with:
              Eerror-number\nerror-message\n

       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, 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 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(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 device specified is ignored.

       Lwhence\noffset\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.

              By issuing the I-1\n0\n command, a client will specify that he is using the VERSION 1 protocol.

              For a VERSION 0 client, the operation parameter is the platform mt_op value (could be different if the client  and
              the rmt server are on two different platforms). For a VERSION 1 client, the operation parameter is standardized as
              below:

              0      Issue a MTWEOF command (write count end-of-file records).

              1      Issue a MTFSF command (forward space over count file marks).

              2      Issue a MTBSF command (backward space over count file marks).

              3      Issue a MTFSR command (forward space count inter-record gaps).

              4      Issue a MTBSR command (backward space count inter-record gaps).

              5      Issue a MTREW command (rewind).

              6      Issue a MTOFFL command (rewind and put the drive offline).

              7      Issue a MTNOP command (no operation, set status only).

       ioperation\ncount\n
              Perform an extended 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.  The  possible  operations
              are:

              0      Issue a MTCACHE command (switch cache on).

              1      Issue a MTNOCACHE command (switch cache off).

              2      Issue a MTRETEN command (retension the tape).

              3      Issue a MTERASE command (erase the entire tape).

              4      Issue a MTEOM command (position to end of media).

              5      Issue a MTNBSF command (backward space count files to BOF).

       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, which is non-portable
              between different platforms).

       ssub-command
              This  is  a  replacement  for the previous S command, portable across different platforms. If the open device is a
              magnetic tape, return members of the magnetic tape status structure, as obtained with a MTIOCGET  ioctl  call.  If
              the open device is not a magnetic tape, an error is returned. If the MTIOCGET operation was successful, the numer-
              ical value of the structure member is returned in decimal. The following sub commands are supported:

              T      return the content of the structure member mt_type which contains the type of the magnetic tape device.

              D      return the content of the structure member mt_dsreg which contains the "drive status register".

              E      return the content of the structure member mt_erreg which contains the  "error  register".  This  structure
                     member must be retrieved first because it is cleared after each MTIOCGET ioctl call.

              R      return the content of the structure member mt_resid which contains the residual count of the last I/O.

              F      return  the  content  of  the structure member mt_fileno which contains the file number of the current tape
                     position.

              B      return the content of the structure member mt_blkno which contains the block number  of  the  current  tape
                     position.

              f      return the content of the structure member mt_flags which contains MTF_ flags from the driver.

              b      return the content of the structure member mt_bf which contains the optimum blocking factor.

       Any other command causes rmt to exit.

DIAGNOSTICS
       All responses are of the form described above.

SEE ALSO
       rcmd(3), rexec(3), /usr/include/sys/mtio.h, rdump(8), rrestore(8)

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

AUTHOR
       The dump/restore backup suit was ported to Linux's Second Extended File System by Remy Card <cardATLinux.Org>. He main-
       tained the initial versions of dump (up and including 0.4b4, released in january 1997).

       Starting with 0.4b5, the new maintainer is Stelian Pop <stelianATpopies.net>.

AVAILABILITY
       The dump/restore backup suit is available from <http://dump.sourceforge.net>;

HISTORY
       The rmt command appeared in 4.2BSD.



BSD                                              version 0.4b43 of June 11, 2010                                          RMT(8)