MT(1) BSD General Commands Manual MT(1)NAMEmt — magnetic tape manipulating program
SYNOPSISmt [-f tapename] command [count]
mt [-f tapename] command argument
DESCRIPTION
The mt utility is used to command a magnetic tape drive for operations
other than reading or writing data.
The -f option's tapename overrides the TAPE environment variable
described below.
The available commands are listed below. Only as many characters as are
required to uniquely identify a command need be specified.
The following commands optionally take a count, which defaults to 1.
weof Write count end-of-file (EOF) marks at the current position.
smk Write count setmarks at the current position (DDS drives only).
fsf Forward space count files.
fsr Forward space count records.
fss Forward space count setmarks (DDS drives only).
bsf Backward space count files.
bsr Backward space count records.
bss Backward space count setmarks (DDS drives only).
erase Erase the tape using a long (often very long) method. With a
count of 0, it will erase the tape using a quick method. Opera‐
tion is not guaranteed if the tape is not at its beginning. The
tape will be at its beginning upon completion.
The following commands ignore count.
rdhpos Read the hardware block position. The block number reported
is specific for that hardware only. With drive data com‐
pression especially, this position may have more to do with
the amount of data sent to the drive than the amount of data
written to tape. Some drives do not support this.
rdspos Read the SCSI logical block position. This typically is
greater than the hardware position by the number of end-of-
file marks. Some drives do not support this.
rewind Rewind the tape.
offline, rewoffl
Rewind the tape and place the drive off line. Some drives
are never off line.
retension Re-tension the tape. This winds the tape from the current
position to the end and then to the beginning. This some‐
times improves subsequent reading and writing, particularly
for streaming drives. Some drives do not support this.
status Output status information about the drive. For SCSI mag‐
netic 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 outputs that. Note that this information is
not definitive (only BOT, End of Recorded Media, and hard‐
ware or SCSI logical block position (if the drive supports
such) are considered definitive tape positions).
errstat Output (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 associ‐
ated status and any residual counts (if any). This command
retrieves and outputs this information. If possible, this
also clears any latched error information.
geteotmodel Output the current EOT filemark model. The model states how
many filemarks will be written at close if a tape was being
written.
eod, eom Wind the tape to the end of the recorded data, typically
after an EOF mark where another file may be written.
The following commands require an argument.
sethpos Set the hardware block position. The argument is a hardware
block number to which to position the tape. Some drives do
not support this.
setspos Set the SCSI logical block position. The argument is a SCSI
logical block number to which to position the tape. Some
drives do not support this.
blocksize Set the block size for the drive. The argument is the num‐
ber of bytes per block, except 0 commands the drive to use
variable-length blocks.
seteotmodel Set the EOT filemark model to argument and output the old
and new models. Typically this will be 2 filemarks, but
some devices (typically QIC cartridge drives) can only write
1 filemark. You may only choose a value of 1 or 2.
comp Set the drive's compression mode. The non-numeric values of
argument are:
off Turn compression off.
on Turn compression on.
none Same as off.
enable Same as on.
IDRC IBM Improved Data Recording Capability compres‐
sion (0x10).
DCLZ DCLZ compression algorithm (0x20).
In addition to the above recognized compression keywords,
the user can supply a numeric compression algorithm for the
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 compres‐
sion algorithm is currently in use), the user can manually
specify one of the supported compression keywords (above),
or supply a numeric compression value from the drive's spec‐
ifications.
density Set the density for the drive. 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 den‐
sity name do not match exactly, an informational message is
output about what the given string has been taken for.
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 density codes are:
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-1350 1,6
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-385M 1,6
0x1D 6.3 (0.25) 32 1,512 (38,400) GCR C QIC-410M 1,6
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)
0x2A
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 Description Type Description
---- -------------------------------------- ---- -----------
NRZI Non return to zero, change on ones R Reel-to-reel
GCR Group code recording C Cartridge
PE Phase encoded CS Cassette
IMFM Inverted modified frequency modulation
MFM Modified frequency modulation
DDS DAT data storage
RLL Run length limited
PRML Partial Response Maximum Likelihood
NOTES
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.
ENVIRONMENT
TAPE This is the pathname of the tape drive. The default (if the vari‐
able is unset, but not if it is null) is /dev/nsa0. It may be
overridden with the -f option.
FILES
/dev/*wt* QIC-02/QIC-36 magnetic tape interface
/dev/*sa[0-9]* SCSI magnetic tape interface
DIAGNOSTICS
The exit status will be 0 when the drive operations were successful, 2
when the drive operations were unsuccessful, and 1 for other problems
like an unrecognized command or a missing drive device.
COMPATIBILITY
Some undocumented commands support old software.
SEE ALSOdd(1), ioctl(2), ast(4), mtio(4), sa(4), environ(7)HISTORY
The mt command appeared in 4.3BSD.
Extensions regarding the st(4) driver appeared in 386BSD 0.1 as a sepa‐
rate st command, and have been merged into the mt command in FreeBSD 2.1.
The former eof command that used to be a synonym for weof has been aban‐
doned in FreeBSD 2.1 since it was often confused with eom, which is
fairly dangerous.
BUGS
The utility cannot be interrupted or killed during a long erase (which
can be longer than an hour), and it is easy to forget that the default
erase is long.
Hardware block numbers do not always correspond to blocks on the tape
when the drive uses internal compression.
Erasure is not guaranteed if the tape is not at its beginning.
Tape-related documentation is poor, here and elsewhere.
BSD January 20, 2008 BSD
