> Linux Man Page: "dd"


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dd - convert and copy a file


dd [OPERAND]...


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

force ibs=BYTES and obs=BYTES

convert BYTES bytes at a time

convert the file as per the comma separated symbol list

copy only BLOCKS input blocks

read BYTES bytes at a time

read from FILE instead of stdin

read as per the comma separated symbol list

write BYTES bytes at a time

write to FILE instead of stdout

write as per the comma separated symbol list

skip BLOCKS obs-sized blocks at start of output

skip BLOCKS ibs-sized blocks at start of input

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

from ASCII to alternate EBCDIC

block pad newline-terminated records with spaces to cbs-size

replace trailing spaces in cbs-size records with newline

lcase change upper case to lower case

do not create the output file

fail if the output file already exists

do not truncate the output file

ucase change lower case to upper case

swap every pair of input bytes

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

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 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

output version information and exit


Written by Paul Rubin, David MacKenzie, and Stuart Kemp.

Reporting Bugs

Report bugs to <>.


Copyright © 2007 Free Software Foundation, Inc. This is free software. You may redistribute copies of it under the terms of the GNU General Public License <>. 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.

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use open software!