RMT(8)							    BSD System Manager's Manual 						    RMT(8)

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 interpro-
     cess 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 indica-
     tion.  All responses are in ASCII and in one of two forms.  Successful commands have responses of:

	   Anumber


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

	   Eerror-number
error-message


     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 '
' indicates that a newline should be supplied:

     Odevice
mode

	     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

	     Close the currently open device.  The devicespecified is ignored.

     Loffset
whence

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

     Wcount

	     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

	     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
 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
count

	     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					 4.2 Berkeley Distribution