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MT (1) | General commands | Unix Manual Pages | :man


mt - magnetic tape manipulating program


See Also


mt [-f tapename] command [count]


The mt utility is used to give commands to a magnetic tape drive. By default mt performs the requested operation once. Operations may be performed multiple times by specifying count.

The available commands are listed below. Only as many characters as are required to uniquely identify a command need be specified.

weof Write count end-of-file marks at the current position on the tape.
smk Write count setmarks at the current position on the tape.
fsf Forward space count files.
fsr Forward space count records.
fss Forward space count setmarks.
bsf Backward space count files.
bsr Backward space count records.
bss Backward space count setmarks.
rdhpos Read Hardware block position. Some drives do not support this. The block number reported is specific for that hardware only. The count argument is ignored.
rdspos Read SCSI logical block position. Some drives do not support this. The count argument is ignored.
sethpos Set Hardware block position. Some drives do not support this. The count argument is interpreted as a hardware block to which to position the tape.
setspos Set SCSI logical block position. Some drives do not support this. The count argument is interpreted as a SCSI logical block to which to position the tape.
rewind Rewind the tape (Count is ignored).
offline, rewoffl
Rewind the tape and place the tape unit off-line (Count is ignored).
erase Erase the tape. A count of 0 disables long erase, which is on by default.
Re-tension the tape (one full wind forth and back, Count is ignored).
status Print status information about the tape unit. For SCSI magnetic tape devices, the current operating modes of density, blocksize, and whether compression is enabled is reported. The current state of the driver (what it thinks that it is doing with the device) is reported. If the driver knows the relative position from BOT (in terms of filemarks and records), it prints that. Note that this information is not definitive (only BOT, End of Recorded Media, and hardware or SCSI logical block position (if the drive supports such) are considered definitive tape positions).
errstat Print (and clear) error status information about this device. For every normal operation (e.g., a read or a write) and every control operation (e.g,, a rewind), the driver stores up the last command executed and it is associated status and any residual counts (if any). This command retrieves and prints this information. If possible, this also clears any latched error information.
Set the block size for the tape unit. Zero means variable-length blocks.
density Set the density for the tape unit. For the density codes, see below. The density value could be given either numerically, or as a string, corresponding to the "Reference" field. If the string is abbreviated, it will be resolved in the order shown in the table, and the first matching entry will be used. If the given string and the resulting canonical density name do not match exactly, an informational message is printed about what the given string has been taken for.
Fetch and print out the current EOT filemark model. The model states how many filemarks will be written at close if a tape was being written.
Set (from the count argument) and print out the current and EOT filemark model. Typically this will be 2 filemarks, but some devices (typically QIC cartridge drives) can only write 1 filemark. Currently you can only choose a value of 1 or 2.
eom Forward space to end of recorded medium (Count is ignored).
eod Forward space to end of data, identical to eom.
comp Set compression mode. There are currently several possible values for the compression mode:

off Turn compression off.
on Turn compression on.
none Same as off.
Same as on.
IDRC IBM Improved Data Recording Capability compression (0x10).
DCLZ DCLZ compression algorithm (0x20).

In addition to the above recognized compression keywords, the user can supply a numeric compression algorithm for the tape drive to use. In most cases, simply turning the compression 'on' will have the desired effect of enabling the default compression algorithm supported by the drive. If this is not the case (see the status display to see which compression algorithm is currently in use), the user can manually specify one of the supported compression keywords (above), or supply a numeric compression value.

If a tape name is not specified, and the environment variable TAPE does not exist; mt uses the device /dev/nsa0.

The mt utility returns a 0 exit status when the operation(s) were successful, 1 if the command was unrecognized, and 2 if an operation failed.

The following density table was taken from the 'Historical sequential access density codes' table (A-1) in Revision 11 of the SCSI-3 Stream Device Commands (SSC) working draft, dated November 11, 1997.

The different density codes are as follows:

"0x0 default for device

"0xE reserved for ECMA

Value Width Tracks Density Code Type Reference Note
mm in bpmm bpi
0x01 12.7 (0.5) 9 32(800) NRZI R X3.22-1983 2
0x02 12.7 (0.5) 9 63 (1,600) PE R X3.39-1986 2
0x03 12.7 (0.5) 9 246 (6,250) GCR R X3.54-1986 2
0x05 6.3 (0.25) 4/9 315 (8,000) GCR C X3.136-1986 1
0x06 12.7 (0.5) 9 126 (3,200) PE R X3.157-1987 2
0x07 6.3 (0.25) 4 252 (6,400) IMFM C X3.116-1986 1
0x08 3.81 (0.15) 4 315 (8,000) GCR CS X3.158-1987 1
0x09 12.7 (0.5) 18 1,491 (37,871) GCR C X3.180 2
0x0A 12.7 (0.5) 22 262 (6,667) MFM C X3B5/86-199 1
0x0B 6.3 (0.25) 4 63 (1,600) PE C X3.56-1986 1
0x0C 12.7 (0.5) 24 500 (12,690) GCR C HI-TC1 1,6
0x0D 12.7 (0.5) 24 999 (25,380) GCR C HI-TC2 1,6
0x0F 6.3 (0.25) 15 394 (10,000) GCR C QIC-120 1,6
0x10 6.3 (0.25) 18 394 (10,000) GCR C QIC-150 1,6
0x11 6.3 (0.25) 26 630 (16,000) GCR C QIC-320 1,6
0x12 6.3 (0.25) 30 2,034 (51,667) RLL C QIC-13501,6
0x13 3.81 (0.15) 1 2,400 (61,000) DDS CS X3B5/88-185A 5
0x14 8.0 (0.315) 1 1,703 (43,245) RLL CS X3.202-1991 5
0x15 8.0 (0.315) 1 1,789 (45,434) RLL CS ECMA TC17 5
0x16 12.7 (0.5) 48 394 (10,000) MFM C X3.193-1990 1
0x17 12.7 (0.5) 48 1,673 (42,500) MFM C X3B5/91-174 1
0x18 12.7 (0.5) 112 1,673 (42,500) MFM C X3B5/92-50 1
0x19 12.7 (0.5) 128 2,460 (62,500) RLL C DLTapeIII 6,7
0x1A 12.7 (0.5) 128 3,214 (81,633) RLL C DLTapeIV(20) 6,7
0x1B 12.7 (0.5) 208 3,383 (85,937) RLL C DLTapeIV(35) 6,7
0x1C 6.3 (0.25) 34 1,654 (42,000) MFM C QIC-385M1,6
0x1D 6.3 (0.25) 32 1,512 (38,400) GCR C QIC-410M1,6
0x1E 6.3 (0.25) 30 1,385 (36,000) GCR C QIC-1000C 1,6
0x1F 6.3 (0.25) 30 2,666 (67,733) RLL C QIC-2100C 1,6
0x20 6.3 (0.25) 144 2,666 (67,733) RLL C QIC-6GB(M) 1,6
0x21 6.3 (0.25) 144 2,666 (67,733) RLL C QIC-20GB(C) 1,6
0x22 6.3 (0.25) 42 1,600 (40,640) GCR C QIC-2GB(C) ?
0x23 6.3 (0.25) 38 2,666 (67,733) RLL C QIC-875M?
0x24 3.81 (0.15) 1 2,400 (61,000) CS DDS-2 5
0x25 3.81 (0.15) 1 3,816 (97,000) CS DDS-3 5
0x26 3.81 (0.15) 1 3,816 (97,000) CS DDS-4 5
0x27 8.0 (0.315) 1 3,056 (77,611) RLL CS Mammoth 5
0x28 12.7 (0.5) 36 1,491 (37,871) GCR C X3.224 1
0x29 12.7 (0.5)
0x2B 12.7 (0.5) 3? ?? C X3.267 5
0x41 12.7 (0.5) 208 3,868 (98,250) RLL C DLTapeIV(40) 6,7
0x48 12.7 (0.5) 448 5,236 (133,000) PRML C SDLTapeI(110) 6,8
0x49 12.7 (0.5) 448 7,598 (193,000) PRML C SDLTapeI(160) 6,8

Code DescriptionType Description
NRZI Non return to zero, change on ones R Reel-to-reel
GCRGroup code recording C Cartridge
PE Phase encodedCS Cassette
IMFM Inverted modified frequency modulation
MFMModified frequency modulation
DDSDAT data storage
RLLRun length limited
PRML Partial Response Maximum Likelihood

1. Serial recorded.
2. Parallel recorded.
3. Old format known as QIC-11.
5. Helical scan.
6. This is not an American National Standard. The reference is based on
an industry standard definition of the media format.
7. DLT recording: serially recorded track pairs (DLTapeIII and
DLTapeIV(20)), or track quads (DLTapeIV(35) and DLTapeIV(40)).
8. Super DLT (SDLT) recording: 56 serially recorded logical tracks with
8 physical tracks each.


If the following environment variable exists, it is utilized by mt.
TAPE The mt utility checks the TAPE environment variable if the argument tapename is not given.


/dev/*wt* QIC-02/QIC-36 magnetic tape interface
/dev/*sa[0-9]* SCSI magnetic tape interface


dd(1), ioctl(2), ast(4), mtio(4), sa(4), environ(7)



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