RMT(8) MachTen System Manager’s Manual RMT(8)

NAME
rmt - remote magtape protocol module

SYNOPSIS
rmt

DESCRIPTION
Rmt 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

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

Eerror-numbererror-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 ‘0 indicates that a
newline should be supplied:

Odevicemode
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
Close the currently open device. The device specified is ig-
nored.

Lwhenceoffset
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-readif 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.

Ioperationcount
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 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
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 2