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MT(1)			FreeBSD	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.  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
		  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	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 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 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.

FreeBSD	10.1		       January 20, 2008			  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | ENVIRONMENT | FILES | DIAGNOSTICS | COMPATIBILITY | SEE ALSO | HISTORY | BUGS

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