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rmt(8)								       rmt(8)



NAME

  rmt -	Allows remote access to	magnetic tape devices

SYNOPSIS

  rmt [debug-output-file]

DESCRIPTION

  The rmt command is started as	a server process when requests from an rdump
  or rrestore call enter the system to operate a storage device	through	an
  interprocess communications connection. After	the remote programs have fin-
  ished, rmt exits and will be started again at	the next request.  The rmt
  command is normally invoked with an rexec or rcmd system call.

  This process performs	the commands described in the following	table and
  responds with	a status indication to tell a user the result of the com-
  manded process. When the rmt command is called with a	filename specified as
  the debug-output-file	parameter, all status responses	are passed to the
  debug-output-file in ASCII and in one	of two possible	formats.  Conse-
  quently, a system administrator can debug both software and hardware prob-
  lems associated with previously issued backup	commands to storage devices.

  Responses to successful commands are in the format:

       Anumber\n

  where	A identifies a normal response,	number is an integer that defines the
  number of the	response as an ASCII integer, and \n is	a newline in the C-
  language idiom.

  Responses to unsuccessful commands are in the	format:

       Eerror_number  error_message\n

  where	E identifies a response	to an error, error_number is one of the	pos-
  sible	error numbers values described in intro(2), error_message is the
  corresponding	error-message string, which is output in response to a call
  to perror(3),	and\n is a newline.

  Debug	information returned by	rmt is stored in the named debug-output-file
  file.	The rmt	command	is called from the rdump or rrestore process with no
  file argument	only when the debug-output-file	parameter is specified.	 To
  activate the debug option of rmt your	system administrator should rename
  the original rmt to rmt.ORG, for example, and	create a new shell executable
  rmt that calls rmt.ORG debug-output-file.






				     Note

       The rdump command starts	remote server /usr/sbin/rmt or /etc/rmt	on
       the client machine to access the	storage	medium.	Another	vendor's
       rdump command may fail because rmt is not located in /etc.  To avoid
       this problem, it	may be necessary to provide a symbolic link on the
       Tru64 UNIX machine pointing to /usr/sbin/rmt as shown in	the following
       example:

	    ln -s /usr/sbin/rmt	/etc/rmt

  All numerical	arguments of the following commands are	transferred as ASCII
  strings:

  O device option
      Opens the	device,	which must be a	full pathname. The option parameter
      is a option value	suitable for the open system call. When	the device is
      successfully opened, the response	is A0\n.

  C device
      Closes the current open device. When this	command	is successful, the
      response is A0\n.

  L offset whence
      Performs a seek operation. The offset and	whence parameters have the
      same significance	as the offset and whence parameters of the lseek sys-
      tem call.	When this command successfully completes, the response is
      An\n, where n has	the same value returned	by a normally successful
      lseek system call.

  W count
      Writes data to the device	(see the O command above). The rmt command
      reads count bytes	from the connection. This process is aborted when an
      EOF (End-of-File)	is detected before the number of characters specified
      by count is transferred. The response to this command is An\n, where n
      is the number of characters written.

  R count
      Reads count bytes	of data	from the open device.  When the	value of
      count exceeds the	size of	the data buffer	(10 kilobytes),	the number of
      characters read is truncated to the data buffer size. The	rmt command
      then does	the requested read operation. The response to this command is
      An\n, where n is the number of characters	read.

  I operation count
      Performs an ioctl	system call on the open	device.	The operation parame-
      ter is a value passed to the mt_op member	of a type mtop structure for
      an MTIOCTOP ioctl	(magnetic tape operation) command. Valid values	for
      the magnetic tape	operations are defined in the /usr/include/sys/mtio.h
      include file.  The count parameter is the	value to pass to the mt_count
      member of	the type mtop structure	and specifies the number of opera-
      tions performed on the tape drive. The response to this command is
      An\n, where n is the count.

  S   Returns the status of the	open device, which is obtained with a
      MTIOCGET ioctl system call. A successful response	to this	command	is
      An\n, where n is the size	of the status buffer, together with the	con-
      tents of the status buffer in binary.









FILES

  /usr/sbin/rmt
      Specifies	the command path

  /usr/include/errno.h
      Describes	the possible error numbers

  /usr/include/sys/mtio.h
      A	header file that defines magnetic tape operations

SEE ALSO

  Commands: rdump(8), rrestore(8)

  Functions: rcmd(3), rexec(3),	open(2), ioctl(2)