DD

NAME
SYNOPSIS
DESCRIPTION
AUTHOR
REPORTING BUGS
COPYRIGHT
SEE ALSO

NAME

dd − convert and copy a file

SYNOPSIS

dd [OPERAND]...
dd OPTION

DESCRIPTION

Copy a file, converting and formatting according to the operands.

bs=BYTES

read and write BYTES bytes at a time (also see ibs=,obs=)

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 (default: 512)

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 (default: 512)

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: c =1, w =2, b =512, kB =1000, K =1024, MB =1000*1000, M =1024*1024, xM =M 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; conv=notrunc suggested)
	direct	use direct I/O for data

directory

fail unless a directory

	dsync		use synchronized I/O for data
	sync		likewise, but also for metadata

fullblock

accumulate full blocks of input (iflag only)

nonblock

use non−blocking I/O

noatime

do not update access time

noctty

do not assign controlling terminal from file

nofollow

do not follow symlinks

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 dd bugs to bug−coreutils@gnu.org
GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
General help using GNU software: <http://www.gnu.org/gethelp/>
Report dd translation bugs to <http://translationproject.org/team/>

COPYRIGHT

Copyright © 2010 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.