---
name: "mt-dds"
section: "1"
platform: "linux"
package: "dds2tar"
version: "2.5.2-7+b1"
release: "Debian 11 (Bullseye)"
platforms: ["linux"]
url: "https://new.carta.tech/mt-dds"
---

# mt-dds(1)

tool to control a dds device.

## NAME

mt-dds - tool to control a dds device.

## SYNOPSIS

**mt-dds** **comp-on**\|**comp-off**\|**comp-query**\|**comp-log**

**mt-dds** \< **tell**\|**label** \> \[ **-b  #** \]

## DESCRIPTION

**mt-dds** controls the compression mode of dds tape devices (DAT).

**mt-dds** may also report the current tape position in absolute records (relative to begin of tape) in a format that may be used later by  **[dds2tar(1)](/dds2tar/1.md)** to access tar archives that are not the first file on tape.

The default device is */dev/nst0*, which may be overridden with the environment variable **TAPE**, which in turn may be overridden with the **-f** *device* option. The device must be a character special file.

## OPTIONS

### DDS tape device control options

- **comp-on**

  Enable the hardware compression mode if supported by the device.

- **comp-off**

  Disable the compression mode, switch to normal mode.

- **comp-query**

  Print to stderr if compression mode currently is disabled  or enabled.  A  **0** means compression is disabled, a **1** means compression in enabled.

- **comp-log**

  Print to stdout four lines of information about transferred kilobytes  before and after hardware compression from and to the device since initialization.

### dds2tar service functions

- **tell**

  Print three lines with the  **current tape position**, a **block size** value (20 by default, may be overridden with  **-b** option) and a  **block length** value (blocksize\*512) to  *stdout*. If this output is redirected to a location file  *locfile*, this file may be used by  **[dds2tar(1)](/dds2tar/1.md)** to access archives on tape.

- **label**

  If the current tape position is the beginning of an archive and the archive is labeled, **mt-dds** writes the label to stdout and moves the tape back to the current position (or back over the filemark).

- **ts**

  If the current tape position is the beginning of an archive and the archive is labeled, **mt-dds** writes the timestamp in octal format to stdout and moves the tape back to the current position (or back over the filemark). If you are using only one computer, the timestamp can be used as a unique archive identifier.

- **-b** **#**

  Specify the block size  *#* value that is used as a default for the written value with the **mt-dds tell** command (see above). Also the internal buffer size is specified with this option which is used to read one block in order to get the block size of the current tape block. So specify the block size of the archive or a larger number.

### other options

- **-f** *device*

  Device of the tape archive (default is /dev/nst0). Must be a character special file connected to a dds tape device.

- **-V**,**--version**

  Print the version number of **mt-dds** to stderr and exit immediately.

- **--help**

  print some screens of online help with examples through a pager and exit immediately.

## EXAMPLES

**Example 1:** checking the compression mode of the default tape device

mt-dds comp-query

**Example 2:** Write the location information as **dds2tar** command line options to stdout.

mt-dds

## ENVIRONMENT

The environment variable **TAPE** overrides the default tape device /dev/nst0.

- PAGER

  The environment variable **PAGER** overrides the builtin pager command ("/bin/more") to display the output of the **--help** option.

## SEE ALSO

[dds2tar(1)](/dds2tar/1.md), [dds2index(1)](/dds2index/1.md), [mt(1)](/mt/1.md), [tar(1)](/tar/1.md)

## HISTORY

This program was created to use it in conjunction with dds2tar.

## AUTHOR

J"org Weule (weule@cs.uni-duesseldorf.de), Phone +49 211 751409. This software is available at ftp.uni-duesseldorf.de:/pub/unix/apollo