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rmt-tar

remote magnetic tape server

rmt

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. Additional data are returned after this line. On error, the following response 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.

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_* constant 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 decimal 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 specified 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 paramedters.
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.

tar(1).

Using this utility as a general-purpose remote file access tool is discouraged.

Report bugs to <bug-tar@gnu.org>.

The rmt command appeared in 4.2BSD. The GNU rmt is written from scratch, using the BSD specification.

Copyright © 2013 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

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