RMT(8) GNU TAR Manual RMT(8)
NAME
rmt - remote magnetic tape server
SYNOPSIS
rmt
DESCRIPTION
Rmt provides remote access to files and devices for tar(1), cpio(1), and
similar backup utilities. It is normally called by running rsh(1) or
ssh(1) to the remote machine, optionally using a different login name if
one is supplied.
The calling program communicates with rmt by sending requests on its
standard input and reading replies from the standard output. A request
consists of a request letter followed by an argument (if required) and a
newline character. Additional data, if any, are sent after the newline.
On success, rmt returns
Anumber\n
where number is an ASCII representation of a decimal return code. Addi-
tional data are returned after this line. On error, the following re-
sponse is returned:
Eerrno\nerror-message\n
where errno is one of the system error codes, as described in errno(3),
and error-message is a one-line human-readable description of the error,
as printed by perror(3).
Available commands and possible responses are discussed in detail in the
subsequent section.
COMMANDS
Odevice\nflags\n
Opens the device with given flags. If a device had already been
opened, it is closed before opening the new one.
Arguments
device The name of the device to open.
flags Flags for open(2): a decimal number, or any valid O_* con-
stant from fcntl.h (the initial O_ may be omitted), or a
bitwise or (using |) of any number of these, e.g.:
576
64|512
CREAT|TRUNC
In addition, a combined form is also allowed, i.e. a deci-
mal mode followed by its symbolic representation. In this
case the symbolic representation is given preference.
Reply
A0\n on success.
Extensions
BSD version allows only decimal number as flags.
C[device]\n
Close the currently open device.
Arguments
Any arguments are silently ignored.
Reply
A0\n on success.
Lwhence\noffset\n
Performs an lseek(2) on the currently open device with the speci-
fied parameters.
Arguments
whence Where to measure offset from. Valid values are:
0, SET, SEEK_SET seek from the file beginning
1, CUR, SEEK_CUR seek from the current location
2, END, SEEK_END seek from the file end
Reply
Aoffset\n on success. The offset is the new offset in
file.
Extensions
BSD version allows only 0,1,2 as whence.
Rcount\n
Read count bytes of data from the current device.
Arguments
count number of bytes to read.
Reply
On success:
Ardcount\n
followed by rdcount bytes of data read from the device.
Wcount\n
Writes data onto the current device. The command is followed by
count bytes of input data.
Arguments
count Number of bytes to write.
Reply
On success: Awrcount\n, where wrcount is the number of
bytes actually written.
Iopcode\ncount\n
Perform a MTIOCOP ioctl(2) command with the specified para-
medters.
Arguments
opcode MTIOCOP operation code.
count mt_count.
Reply
On success: A0\n.
S\n Returns the status of the currently open device, as obtained from
a MTIOCGET ioctl(2) call.
Arguments
None
Reply
On success: Acount\n followed by count bytes of data.
SEE ALSO
tar(1).
BUGS
Using this utility as a general-purpose remote file access tool is dis-
couraged.
BUG REPORTS
Report bugs to <bug-tar@gnu.org>.
HISTORY
The rmt command appeared in 4.2BSD. The GNU rmt is written from
scratch, using the BSD specification.
COPYRIGHT
Copyright © 2013, 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/li-
censes/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
RMT March 24, 2018 RMT(8)
Generated by dwww version 1.16 on Tue Dec 16 04:39:14 CET 2025.