dd
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 | This is the JargonFile (V4.00) entry for dd - Next: DDT, Prev: day mode |
| :dd: /dee-dee/ /vt./ [[[Unix]]: from IBM JCL] Equivalent to cat or BLT. Originally the name of a Unix copy command with special options suitable for block-oriented devices; it was often used in heavy-handed system maintenance, as in "Lets dd the root partition onto a tape, then use the boot PROM to load it back on to a new disk". The Unix dd(1) was designed with a weird, distinctly non-Unixy keyword option syntax reminiscent of IBM System/360 JCL (which had an elaborate DD Dataset Definition specification for I/O devices); though the command filled a need, the interface design was clearly a prank. The jargon usage is now very rare outside Unix sites and now nearly obsolete even there, as dd(1) has been deprecated for a long time (though it has no exact replacement). The term has been displaced by BLT or simple English copy. | |
| * (text is auto-included via JargonExtension by mutante using jargon with VERSION 4.0.0, 24 JUL 1996 - JargonFile by Eric S. Raymond is in the public domain) | |
| Table of contents |
NAME
dd - convert and copy a fileSYNOPSIS
dd [OPERAND]...dd OPTION
DESCRIPTION
Copy a file, converting and formatting according to the operands.
- bs=BYTES
- force ibs=BYTES and obs=BYTES
- cbs=BYTES
- convert BYTES bytes at a time
- conv=CONVS
- convert the file as per the comma separated symbol list
- count=BLOCKS
- copy only BLOCKS input blocks
- ibs=BYTES
- read BYTES bytes at a time
- if=FILE
- read from FILE instead of stdin
- iflag=FLAGS
- read as per the comma separated symbol list
- obs=BYTES
- write BYTES bytes at a time
- of=FILE
- write to FILE instead of stdout
- oflag=FLAGS
- write as per the comma separated symbol list
- seek=BLOCKS
- skip BLOCKS obs-sized blocks at start of output
- skip=BLOCKS
- skip BLOCKS ibs-sized blocks at start of input
- status=noxfer
- suppress transfer statistics
BLOCKS and BYTES may be followed by the following multiplicative suffixes: xM M, c 1, w 2, b 512, kB 1000, K 1024, MB 1000*1000, M 1024*1024, GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E, Z, Y.
Each CONV symbol may be:
- ascii
- from EBCDIC to ASCII
- ebcdic
- from ASCII to EBCDIC
- ibm
- from ASCII to alternate EBCDIC
- block
- pad newline-terminated records with spaces to cbs-size
- unblock
- replace trailing spaces in cbs-size records with newline
- lcase
- change upper case to lower case
- nocreat
- do not create the output file
- excl
- fail if the output file already exists
- notrunc
- do not truncate the output file
- ucase
- change lower case to upper case
- swab
- swap every pair of input bytes
- noerror
- continue after read errors
- sync
- pad every input block with NULs to ibs-size; when used
- with block or unblock, pad with spaces rather than NULs
- fdatasync physically write output file data before finishing fsync likewise, but also write metadata
Each FLAG symbol may be:
- append
- append mode (makes sense only for output)
- direct
- use direct I/O for data
- dsync
- use synchronized I/O for data
- sync
- likewise, but also for metadata
- nonblock
- use non-blocking I/O
- nofollow
- do not follow symlinks
- noctty
- do not assign controlling terminal from file
Sending a USR1 signal to a running `dd' process makes it print I/O statistics to standard error and then resume copying.
- $ dd if=/dev/zero of=/dev/null& pid=$!
$ kill -USR1 $pid; sleep 1; kill $pid - 18335302+0 records in 18335302+0 records out 9387674624 bytes (9.4 GB) copied, 34.6279 seconds, 271 MB/s
Options are:
- --help
- display this help and exit
- --version
- output version information and exit
AUTHOR
Written by Paul Rubin, David MacKenzie, and Stuart Kemp.REPORTING BUGS
Report bugs to <bug-coreutils@gnu.org>.COPYRIGHT
Copyright © 2006 Free Software Foundation, Inc.This is free software. You may redistribute copies of it under the terms of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>. There is NO WARRANTY, to the extent permitted by law.
SEE ALSO
The full documentation for dd is maintained as a Texinfo manual. If the info and dd programs are properly installed at your site, the command- info dd
should give you access to the complete manual.
Index
Updated Time:: 15:19:05 GMT, November 23, 2008
