dd - convert and copy a file




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

bs=BYTES read and write up to BYTES bytes at a time

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 up to 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

ucase change lower case to upper case

swab swap every pair of input bytes

sync pad every input block with NULs to ibs-size; when used with block or unblock, pad with spaces rather than NULs

excl fail if the output file already exists

nocreat do not create the output file

notrunc do not truncate the output file

noerror continue after read errors

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

nocache discard cached data

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.


Report dd bugs to
GNU coreutils home page: <> General help using GNU software: <> Report dd translation bugs to <>


Copyright (C) 2011 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.


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 coreutils 'dd invocation'

should give you access to the complete manual.