---
name: "rmt"
section: "8"
platform: "linux"
package: "tar"
version: "1.35-5"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "openbsd"]
url: "https://new.carta.tech/rmt"
---

# rmt(8)

remote magnetic tape server

## NAME

rmt - remote magnetic tape server

## SYNOPSIS

**rmt**

## DESCRIPTION

**Rmt** provides remote access to files and devices for [**tar**(1)](/tar/1.md), [**cpio**(1)](/cpio/1.md), and similar backup utilities.  It is normally called by running [**rsh**(1)](/rsh/1.md) or [**ssh**(1)](/ssh/1.md) 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)](/errno/3.md), and *error-message* is a one-line human-readable description of the error, as printed by [**perror**(3)](/perror/3.md).

Available commands and possible responses are discussed in detail in the subsequent section.

## COMMANDS

- **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)](/open/2.md): 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.

  - **L***whence***\\n***offset***\\n**

    Performs an [**lseek**(2)](/lseek/2.md) 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)](/ioctl/2.md) 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)](/ioctl/2.md) call.

    - **Arguments**

      None

    - **Reply**

      On success: **A***count***\\n** followed by *count* bytes of data.

## SEE ALSO

[**tar**(1)](/tar/1.md).

## BUGS

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

## 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/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.