RMT(8) BSD System Manager's Manual RMT(8)NAMErmt — remote magtape protocol module
SYNOPSISrmtDESCRIPTIONrmt is a program used by the remote dump and restore programs in manipu‐
lating a magnetic tape drive through an interprocess communication con‐
nection. 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 two forms. Successful commands
have responses of:
Anumber\n
Number is an ASCII representation of a decimal number. Unsuccessful com‐
mands are responded to with:
Eerror-number\nerror-message\n
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 comprises 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 new‐
line 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.
Loffset\nwhence\n
Perform an lseek(2) operation using the specified parameters.
The response value is that returned from the lseek(2) 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(2) 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(2) 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 ALSOrcmd(3), rexec(3), mtio(4), rdump(8), rrestore(8)HISTORY
The rmt command appeared in 4.2BSD.
BUGS
People should be discouraged from using this for a remote file access
protocol.
BSD June 1, 1994 BSD
