mt-dds < tell|label > [ -b # ]
DESCRIPTIONmt-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) 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.
DDS tape device control options
- Enable the hardware compression mode if supported by the device.
- Disable the compression mode, switch to normal mode.
- Print to stderr if compression mode currently is disabled or enabled. A 0 means compression is disabled, a 1 means compression in enabled.
- 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
- 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) to access archives on tape.
- 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).
- 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.
- -f device
- Device of the tape archive (default is /dev/nst0). Must be a character special file connected to a dds tape device.
- Print the version number of mt-dds to stderr and exit immediately.
- print some screens of online help with examples through a pager and exit immediately.
EXAMPLESExample 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.
ENVIRONMENTThe environment variable TAPE overrides the default tape device /dev/nst0.
- The environment variable PAGER overrides the builtin pager command ("/bin/more") to display the output of the --help option.