rmt - remote magtape protocol module
rmt is a program used by the remote dump and restore programs in manip-
ulating a magnetic tape drive through an interprocess communication
connection. rmt is normally started up with an rexec(3N) or rcmd(3N)
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 two forms. Successful
commands have responses of
where number is an ASCII representation of a decimal number. Unsuc-
cessful commands are responded to with
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
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
Cdevice Close the currently open device. The device
specified is ignored.
Perform a MTIOCOP ioctl(2) command using the
specified parameters. The parameters are inter-
preted as the ASCII representations of the deci-
mal 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.
Perform an lseek(2V) operation using the speci-
fied parameters. The response value is that
returned from the lseek call.
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(2V). If a device had already
been opened, it is closed before a new open is
Rcount Read count bytes of data from the open device.
rmt performs the requested read(2V) and responds
with Acount-read\n 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.
Wcount Write data onto the open device. rmt reads count
bytes from the connection, aborting if a prema-
ture EOF is encountered. The response value is
that returned from the write(2V) call.
Any other command causes rmt to exit.
All responses are of the form described above.
intro(2), ioctl(2), lseek(2V), open(2V), read(2V), write(2V), per-
ror(3), rcmd(3N), rexec(3N), mtio(4), dump(8), restore(8)
People tempted to use this for a remote file access protocol are dis-
26 May 1988 RMT(8C)