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DD(1)			FreeBSD	General	Commands Manual			 DD(1)

NAME
     dd	-- convert and copy a file

SYNOPSIS
     dd	[operands ...]

DESCRIPTION
     The dd utility copies the standard	input to the standard output.  Input
     data is read and written in 512-byte blocks.  If input reads are short,
     input from	multiple reads are aggregated to form the output block.	 When
     finished, dd displays the number of complete and partial input and	output
     blocks and	truncated input	records	to the standard	error output.

     The following operands are	available:

     bs=n     Set both input and output	block size to n	bytes, superseding the
	      ibs and obs operands.  If	no conversion values other than
	      noerror, notrunc or sync are specified, then each	input block is
	      copied to	the output as a	single block without any aggregation
	      of short blocks.

     cbs=n    Set the conversion record	size to	n bytes.  The conversion
	      record size is required by the record oriented conversion	val-
	      ues.

     count=n  Copy only	n input	blocks.

     files=n  Copy n input files before	terminating.  This operand is only
	      applicable when the input	device is a tape.

     fillchar=c
	      When padding a block in conversion mode or due to	use of noerror
	      and sync modes, fill with	the specified ASCII character, rather
	      than using a space or NUL.

     ibs=n    Set the input block size to n bytes instead of the default 512.

     if=file  Read input from file instead of the standard input.

     iseek=n  Seek on the input	file n blocks.	This is	synonymous with
	      skip=n.

     obs=n    Set the output block size	to n bytes instead of the default 512.

     of=file  Write output to file instead of the standard output.  Any	regu-
	      lar output file is truncated unless the notrunc conversion value
	      is specified.  If	an initial portion of the output file is
	      seeked past (see the oseek operand), the output file is trun-
	      cated at that point.

     oseek=n  Seek on the output file n	blocks.	 This is synonymous with
	      seek=n.

     seek=n   Seek n blocks from the beginning of the output before copying.
	      On non-tape devices, an lseek(2) operation is used.  Otherwise,
	      existing blocks are read and the data discarded.	If the user
	      does not have read permission for	the tape, it is	positioned
	      using the	tape ioctl(2) function calls.  If the seek operation
	      is past the end of file, space from the current end of file to
	      the specified offset is filled with blocks of NUL	bytes.

     skip=n   Skip n blocks from the beginning of the input before copying.
	      On input which supports seeks, an	lseek(2) operation is used.
	      Otherwise, input data is read and	discarded.  For	pipes, the
	      correct number of	bytes is read.	For all	other devices, the
	      correct number of	blocks is read without distinguishing between
	      a	partial	or complete block being	read.

     conv=value[,value ...]
	      Where value is one of the	symbols	from the following list.

	      ascii, oldascii
		       The same	as the unblock value except that characters
		       are translated from EBCDIC to ASCII before the records
		       are converted.  (These values imply unblock if the op-
		       erand cbs is also specified.)  There are	two conversion
		       maps for	ASCII.	The value ascii	specifies the recom-
		       mended one which	is compatible with AT&T	System V UNIX.
		       The value oldascii specifies the	one used in historic
		       AT&T UNIX and pre-4.3BSD-Reno systems.

	      block    Treats the input	as a sequence of newline or end-of-
		       file terminated variable	length records independent of
		       input and output	block boundaries.  Any trailing	new-
		       line character is discarded.  Each input	record is con-
		       verted to a fixed length	output record where the	length
		       is specified by the cbs operand.	 Input records shorter
		       than the	conversion record size are padded with spaces.
		       Input records longer than the conversion	record size
		       are truncated.  The number of truncated input records,
		       if any, are reported to the standard error output at
		       the completion of the copy.

	      ebcdic, ibm, oldebcdic, oldibm
		       The same	as the block value except that characters are
		       translated from ASCII to	EBCDIC after the records are
		       converted.  (These values imply block if	the operand
		       cbs is also specified.)	There are four conversion maps
		       for EBCDIC.  The	value ebcdic specifies the recommended
		       one which is compatible with AT&T System	V UNIX.	 The
		       value ibm is a slightly different mapping, which	is
		       compatible with the AT&T	System V UNIX ibm value.  The
		       values oldebcdic	and oldibm are maps used in historic
		       AT&T UNIX and pre-4.3BSD-Reno systems.

	      lcase    Transform uppercase characters into lowercase charac-
		       ters.

	      pareven, parnone,	parodd,	parset
		       Output data with	the specified parity.  The parity bit
		       on input	is stripped unless EBCDIC to ASCII conversions
		       is also specified.

	      noerror  Do not stop processing on an input error.  When an
		       input error occurs, a diagnostic	message	followed by
		       the current input and output block counts will be writ-
		       ten to the standard error output	in the same format as
		       the standard completion message.	 If the	sync conver-
		       sion is also specified, any missing input data will be
		       replaced	with NUL bytes (or with	spaces if a block ori-
		       ented conversion	value was specified) and processed as
		       a normal	input buffer.  If the fillchar option is spec-
		       ified, the fill character provided on the command line
		       will override the automatic selection of	the fill char-
		       acter.  If the sync conversion is not specified,	the
		       input block is omitted from the output.	On input files
		       which are not tapes or pipes, the file offset will be
		       positioned past the block in which the error occurred
		       using lseek(2).

	      notrunc  Do not truncate the output file.	 This will preserve
		       any blocks in the output	file not explicitly written by
		       dd.  The	notrunc	value is not supported for tapes.

	      osync    Pad the final output block to the full output block
		       size.  If the input file	is not a multiple of the out-
		       put block size after conversion,	this conversion	forces
		       the final output	block to be the	same size as preceding
		       blocks for use on devices that require regularly	sized
		       blocks to be written.  This option is incompatible with
		       use of the bs=n block size specification.

	      sparse   If one or more output blocks would consist solely of
		       NUL bytes, try to seek the output file by the required
		       space instead of	filling	them with NULs,	resulting in a
		       sparse file.

	      swab     Swap every pair of input	bytes.	If an input buffer has
		       an odd number of	bytes, the last	byte will be ignored
		       during swapping.

	      sync     Pad every input block to	the input buffer size.	Spaces
		       are used	for pad	bytes if a block oriented conversion
		       value is	specified, otherwise NUL bytes are used.

	      ucase    Transform lowercase characters into uppercase charac-
		       ters.

	      unblock  Treats the input	as a sequence of fixed length records
		       independent of input and	output block boundaries.  The
		       length of the input records is specified	by the cbs op-
		       erand.  Any trailing space characters are discarded and
		       a newline character is appended.

     Where sizes are specified,	a decimal, octal, or hexadecimal number	of
     bytes is expected.	 If the	number ends with a ``b'', ``k'', ``m'',	``g'',
     or	``w'', the number is multiplied	by 512,	1024 (1K), 1048576 (1M),
     1073741824	(1G) or	the number of bytes in an integer, respectively.  Two
     or	more numbers may be separated by an ``x'' to indicate a	product.

     When finished, dd displays	the number of complete and partial input and
     output blocks, truncated input records and	odd-length byte-swapping
     blocks to the standard error output.  A partial input block is one	where
     less than the input block size was	read.  A partial output	block is one
     where less	than the output	block size was written.	 Partial output	blocks
     to	tape devices are considered fatal errors.  Otherwise, the rest of the
     block will	be written.  Partial output blocks to character	devices	will
     produce a warning message.	 A truncated input block is one	where a	vari-
     able length record	oriented conversion value was specified	and the	input
     line was too long to fit in the conversion	record or was not newline ter-
     minated.

     Normally, data resulting from input or conversion or both are aggregated
     into output blocks	of the specified size.	After the end of input is
     reached, any remaining output is written as a block.  This	means that the
     final output block	may be shorter than the	output block size.

     If	dd receives a SIGINFO (see the status argument for stty(1)) signal,
     the current input and output block	counts will be written to the standard
     error output in the same format as	the standard completion	message.  If
     dd	receives a SIGINT signal, the current input and	output block counts
     will be written to	the standard error output in the same format as	the
     standard completion message and dd	will exit.

EXIT STATUS
     The dd utility exits 0 on success,	and >0 if an error occurs.

EXAMPLES
     Check that	a disk drive contains no bad blocks:

	   dd if=/dev/ad0 of=/dev/null bs=1m

     Do	a refresh of a disk drive, in order to prevent presently recoverable
     read errors from progressing into unrecoverable read errors:

	   dd if=/dev/ad0 of=/dev/ad0 bs=1m

     Remove parity bit from a file:

	   dd if=file conv=parnone of=file.txt

     Check for (even) parity errors on a file:

	   dd if=file conv=pareven | cmp -x - file

SEE ALSO
     cp(1), mt(1), tr(1), geom(4)

STANDARDS
     The dd utility is expected	to be a	superset of the	IEEE Std 1003.2
     (``POSIX.2'') standard.  The files	operand	and the	ascii, ebcdic, ibm,
     oldascii, oldebcdic and oldibm values are extensions to the POSIX stan-
     dard.

BUGS
     Protection	mechanisms in the geom(4) subsystem might prevent the super-
     user from writing blocks to a disk.  Instructions for temporarily dis-
     abling these protection mechanisms	can be found in	the geom(4) manpage.

FreeBSD	9.3			August 15, 2004			   FreeBSD 9.3

NAME | SYNOPSIS | DESCRIPTION | EXIT STATUS | EXAMPLES | SEE ALSO | STANDARDS | BUGS

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