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(3X) or rcmd(3X)
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
commands (a space is present between each token).
O device mode Open the specified device using the indicated mode.
Device is a full pathname and mode is an ASCII represen-
tation 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.
C device Close the currently open device. The device specified
L whence offset
Perform an lseek(2) operation using the specified param-
eters. The response value is that returned from the
W count 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.
R count 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; otherwise an error in the stan-
dard format is returned. If the read was successful,
the data read is then sent.
I operation 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.
All responses are of the form described above.
rcmd(3X), rexec(3X), mtio(4), rdump(8C), rrestore(8C)
People tempted to use this for a remote file access protocol are dis-
4th Berkeley Distribution 4 March 1983 RMT(8C)