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) pro-
       grams 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  mag-
       netic tapes, performs the commands, then responds with a status indica-
       tion.  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	 argu-
       ments, 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; oth-
	      erwise  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  parame-
	      ters.   The  parameters are interpreted as the ASCII representa-
	      tions 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  off-
		     line).

	      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	repre-
	      sentations  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 suc-
	      cessful. 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 MTI-
	      OCGET 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 numerical 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 MTI-
		     OCGET 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	 posi-
		     tion.

	      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 <card@Linux.EU.Org>. He maintained the initial ver-
       sions of dump (up and including 0.4b4, released in january 1997).

       Starting	   with	  0.4b5,   the	 new   maintainer   is	 Stelian   Pop
       <stelian@popies.net>.

AVAILABILITY
       The dump/restore backup suit  is	 available  from  <http://dump.source-
       forge.net>

HISTORY
       The rmt command appeared in 4.2BSD.



BSD			version 0.4b42 of June 18, 2009			RMT(8)