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RMT(8)				 GNU TAR Manual 			  RMT(8)

NAME
     rmt - remote magnetic tape server

SYNOPSIS
     rmt

DESCRIPTION
     Rmt  provides  remote  access to files and devices for tar(1), cpio(1), and
     similar backup utilities.	It is  normally  called  by  running  rsh(1)  or
     ssh(1)  to  the  remote machine, optionally using a different login name if
     one is supplied.

     The calling program communicates with rmt by sending requests on its  stan-
     dard  input  and  reading replies from the standard output.  A request con-
     sists of a request letter followed by an argument (if required) and a  new-
     line  character.	Additional data, if any, are sent after the newline.  On
     success, rmt returns

	 Anumber\n

     where number is an ASCII representation of a decimal  return  code.   Addi-
     tional data are returned after this line.	On error, the following response
     is returned:

	 Eerrno\nerror-message\n

     where errno is one of the system error codes, as described in errno(3), and
     error-message  is	a  one-line  human-readable description of the error, as
     printed by perror(3).

     Available commands and possible responses are discussed in  detail  in  the
     subsequent section.

COMMANDS
     Odevice\nflags\n
	    Opens  the	device	with  given  flags. If a device had already been
	    opened, it is closed before opening the new one.

	    Arguments

	    device
		   The name of the device to open.

	    flags  Flags for open(2): a decimal number, or any	valid  O_*  con-
		   stant from fcntl.h (the initial O_ may be omitted), or a bit-
		   wise or (using |) of any number of these, e.g.:
		       576
		       64|512
		       CREAT|TRUNC
		   In  addition, a combined form is also allowed, i.e. a decimal
		   mode followed by its symbolic representation.  In  this  case
		   the symbolic representation is given preference.

	    Reply
		   A0\n on success.

	    Extensions
		   BSD version allows only decimal number as flags.

     C[device]\n
	    Close the currently open device.

	    Arguments
		   Any arguments are silently ignored.

	    Reply
		   A0\n on success.

     Lwhence\noffset\n
	    Performs an lseek(2) on the currently open device with the specified
	    parameters.

	    Arguments

		   whence
			  Where to measure offset from. Valid values are:

			   0, SET, SEEK_SET   seek from the file beginning
			   1, CUR, SEEK_CUR   seek from the current location
			   2, END, SEEK_END   seek from the file end

	    Reply
		   Aoffset\n on success. The offset is the new offset in file.

	    Extensions
		   BSD version allows only 0,1,2 as whence.

     Rcount\n
	    Read count bytes of data from the current device.

	    Arguments

		   count  number of bytes to read.

	    Reply
		   On success:

		       Ardcount\n

		   followed by rdcount bytes of data read from the device.

     Wcount\n
	    Writes  data  onto	the  current device.  The command is followed by
	    count bytes of input data.

	    Arguments

		   count  Number of bytes to write.

	    Reply
		   On success: Awrcount\n, where wrcount is the number of  bytes
		   actually written.

     Iopcode\ncount\n
	    Perform a MTIOCOP ioctl(2) command with the specified paramedters.

	    Arguments

		   opcode
			  MTIOCOP operation code.

		   count  mt_count.

	    Reply
		   On success: A0\n.

     S\n    Returns  the status of the currently open device, as obtained from a
	    MTIOCGET ioctl(2) call.

	    Arguments
		   None

	    Reply
		   On success: Acount\n followed by count bytes of data.

SEE ALSO
     tar(1).

BUGS
     Using this utility as a general-purpose remote file access tool is discour-
     aged.

BUG REPORTS
     Report bugs to <bug-tar@gnu.org>.

HISTORY
     The rmt command appeared in 4.2BSD.  The GNU rmt is written  from	scratch,
     using the BSD specification.

COPYRIGHT
     Copyright (C) 2013, 2018 Free Software Foundation, Inc.
     License GPLv3+: GNU GPL version 3 or later <http://gnu.org/li-
     censes/gpl.html>
     This  is  free software: you are free to change and redistribute it.  There
     is NO WARRANTY, to the extent permitted by law.

RMT				 March 24, 2018 			  RMT(8)

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