Manpages - rmt.8

rmt - 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

A*/number/\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:

E*/errno/\n*/error-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.

O*/device/\n*/flags/*\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

#+begin_quote 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.

L*/whence/\n*/offset/*\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

A*/offset/\n* on success. The offset is the new offset in file.

Extensions

BSD version allows only 0,1,2 as whence.

R*/count/\n*

Read count bytes of data from the current device.

Arguments

count

number of bytes to read.

Reply

On success:

A*/rdcount/\n*

followed by rdcount bytes of data read from the device.

W*/count/\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: A*/wrcount/\n*, where wrcount is the number of bytes actually written.

I*/opcode/\n*/count/*\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: A*/count/\n* followed by count bytes of data.

#+end_quote

*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, 2018 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.