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dd(1)									 dd(1)

       dd - copy and convert data

       dd [option = value...]

       The  command  copies an input file to an output file with any requested
       conversions.  The command is especially suited to I/O on the raw physi‐
       cal  devices  because it allows reading and writing in arbitrary record

       After completion, reports the number of whole  and  partial  input  and
       output blocks.

       The  utility  supports  EOT  handling  which allows the use of multiple
       media.  When writing, the utility prompts for the next volume  when  it
       encounters the end of the current volume.  When reading multivolume ar‐
       chives, the utility requires that the user specify the number  of  vol‐
       umes in the tape set.

       This  utility supports the TA90 style sequential stacker loader device.
       The device ejects a cartridge when it is taken off line.	 This  utility
       performs the device ejection on behalf of the user when it encounters a
       multivolume boundary during write or read  operations  involving	 tape.
       The  device  then automatically loads the next available tape (if there
       is one).	 The utility then attempts to access this tape before  prompt‐
       ing the user for a manual reload operation.

       Where  sizes (n) are given for an option, the number may end with k for
       kilobytes (1024 bytes), b for blocks (512 bytes), or  w	for  words  (2
       bytes).	Also, two numbers may be separated by the character x to indi‐
       cate a product.

       mv=n		   The number of tapes in a multivolume tape set.

       if=name		   Input  file	name.	The  standard  input  is   the

       of=name		   Output  file	 name.	 The  standard	output	is the

       ibs=n		   Input block size,  n	 bytes.	 The  default  is  512
			   bytes.   Some  devices  do not support greater than
			   65,535 bytes.

       obs=n		   Output block size, n bytes.	 The  default  is  512
			   bytes.   Some  devices  do not support greater than
			   65,535 bytes.

       bs=n		   Set both input and output block size	 to  n	bytes,
			   superseding ibs and obs.  Also, if bs is specified,
			   the copy is more efficient, since no blocking  con‐
			   version is necessary.

       cbs=n		   Conversion  buffer  size,  n	 bytes.	  Use  only if
			   ascii, unblock, ebcdic, ibm, or block conversion is
			   specified.  For ascii and unblock, n characters are
			   placed into the conversion  buffer,	any  specified
			   character  mapping  is  done,  trailing  blanks are
			   trimmed and new line added before sending the  line
			   to  the output.  For ebcdic, ibm, or block, charac‐
			   ters are  read  into	 the  conversion  buffer,  and
			   blanks  added  to  make  an output record of size n

       skip=n		   Skip n input records before starting to copy.

       files=n		   Copy n input files before terminating.  This option
			   is useful only when the input is a magnetic tape or
			   similar device.

       seek=n		   Seek n records from beginning of output file before

       rbuf=n		   Use	n  buffers  for reading from those raw devices
			   that support n-buffered I/O.	 (See Reference	 Pages
			   Section  4:	Special	 Files to check whether a spe‐
			   cific device supports n-buffered I/O.)  All n reads
			   are	started and each read must complete before the
			   data can be used.  This allows an n-buffered	 read-
			   ahead on supported raw devices.

			   A  default  of  eight  read buffers are used if the
			   read device supports n-buffered I/O and  the	 write
			   device does not.

			   The	rbuf  option  cannot  be  used	with  the wbuf

       wbuf=n		   Use n buffers for writing from  those  raw  devices
			   that	 support n-buffered I/O.  (See Reference Pages
			   Section 4: Special Files to check  whether  a  spe‐
			   cific  device supports n-buffered I/O.)  Each write
			   is started but not known to be complete until all n
			   buffers have been used.  (This allows an n-buffered
			   write-behind on supported raw devices).

			   A default of eight write buffers are	 used  if  the
			   write device supports n-buffered I/O.

			   The	wbuf  option  cannot  be  used	with  the rbuf

       count=n		   Copy only n input records.

       conv=ascii	   Convert EBCDIC to ASCII.

       conv=ebcdic	   Convert ASCII to EBCDIC.

       conv=ibm		   Slightly different map  of  ASCII  to  EBCDIC  (see

       conv=block	   Convert variable length records to fixed length.

       conv=unblock	   Convert fixed length records to variable length.

       conv=lcase	   Map alphabetics to lowercase.

       conv=ucase	   Map alphabetics to uppercase.

       conv=loader	   Permits  the	 program  to treat the tape drive as a
			   sequential loader device even though it is not rep‐
			   resented as such in the system driver tables.

       conv=swab	   Swap every pair of bytes.

       conv=noerror	   Do not stop processing on an error.

       conv=sync	   Pad every input record to ibs.

       conv=nomulti	   Disable multiple tape volumes.

       conv=sparse	   Create a sparse output file.

       conv=... , ...	   Include several arguments for the conv option, sep‐
			   arated by commas (see example below).

       The ASCII/EBCDIC conversion tables are  taken  from  the	 256-character
       standard in the Communications of the ACM, November, 1968.

       The ibm conversion corresponds to certain IBM print train conventions.

       One  must specify ``conv=noerror,sync'' when copying raw disks with bad
       sectors to ensure that stays synchronized.

       Do not specify a block size greater than 65535  bytes  when  performing
       device I/O with the TK50 device.	 This device gives an I/O error when a
       size greater than 65535 is given.  If you attempt to give a block  size
       larger than 65535 on other devices and the device returns an I/O error,
       try using the maximum size of 65535 bytes.

       Also, the buffering scheme employed by the VAX and device drivers  lim‐
       its the block size to 16 Kbytes.

       Furthermore,  when writing to tapes, do not use an odd block size value
       when specifying the blocking factor.  This  can	result	in  characters
       being dropped on every second block written to the tape.

       We  recommend that users label their tapes to include the values speci‐
       fied in the obs or bs options of the command.  This ensures the ability
       to  correctly  specify the tape blocksize in the ibs or bs options used
       to read the tape at a later date.  The  command	does  not  attempt  to
       autosize	 the  tape.   Thus,  if	 the  user accidentally uses a smaller
       blocksize when reading the tape, the command would  appear  to  succeed
       (reporting  no  errors),	 but  the effect would be to truncate the tape
       records on output.

       Using a blocking factor other than the default may lead to higher  per‐
       formance.  However, you must select a value that is compatible with the
       hardware limitations of the source and destination machines.

       The following example shows how to read	an  EBCDIC  tape  blocked  ten
       80-byte EBCDIC card images per record into the ASCII file x:
       dd if=/dev/rmt0h of=x ibs=800 cbs=80 conv=ascii,lcase

       Note  the use of raw magtape.  As noted in the Description, the command
       is especially suited to I/O on the  raw	physical  devices  because  it
       allows reading and writing in arbitrary record sizes.

       f+p records in(out): numbers of full and partial records read(written)

See Also
       cp(1), tr(1), nbuf(4)


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