MT(1)							    BSD General Commands Manual 						     MT(1)

NAME

     mt -- magnetic tape manipulating program

SYNOPSIS

     mt [-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.  Operation 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 compression
		  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 sometimes
		  improves subsequent reading and writing, particularly for streaming drives.  Some drives do not support this.

     status	  Output status information about the drive.  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 outputs 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	  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 associated status and any residual
		  counts (if any).  This command retrieves and outputs this information.  If possible, this also clears any latched error informa-
		  tion.

     geteotmodel  Output the current EOT filemark model.  The model states how many filemarks will be written at close if a tape was being writ-
		  ten.

     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 number 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 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 drive to
		  use.	In most cases, simply turning the compression 'on' will have the desired effect of enabling the default compression algo-
		  rithm 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
		  from the drive's specifications.

     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 density 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 variable is unset, but not if it is null) is /dev/nsa0.  It may be over-
	   ridden 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 ALSO

     dd(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 separate 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 abandoned 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