rmt is a program used by the remote dump and restore programs in manipulating a magnetic tape drive through an interprocess communication connection.
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 commands 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 newline 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; otherwise 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 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(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.