DD
Section: User Commands (1)
Updated: February 2026
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NAME
dd - convert and copy a file
SYNOPSIS
dd
[
,OPERAND/]...
dd
,OPTION/
DESCRIPTION
Copy a file, converting and formatting according to the operands.
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddbs'bs=BYTESX'tty: link'
-
read and write up to BYTES bytes at a time (default: 512);
overrides ibs and obs
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddcbs'cbs=BYTESX'tty: link'
-
convert BYTES bytes at a time
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddconv'conv=CONVSX'tty: link'
-
convert the file as per the comma separated symbol list
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddcount'count=NX'tty: link'
-
copy only N input blocks
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddibs'ibs=BYTESX'tty: link'
-
read up to BYTES bytes at a time (default: 512)
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddif'if=FILEX'tty: link'
-
read from FILE instead of standard input
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddiflag'iflag=FLAGSX'tty: link'
-
read as per the comma separated symbol list
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddobs'obs=BYTESX'tty: link'
-
write BYTES bytes at a time (default: 512)
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddof'of=FILEX'tty: link'
-
write to FILE instead of standard output
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddoflag'oflag=FLAGSX'tty: link'
-
write as per the comma separated symbol list
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddseek'seek=NX'tty: link'
-
(or oseek=N) skip N obs sized output blocks
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddskip'skip=NX'tty: link'
-
(or iseek=N) skip N ibs sized input blocks
- X'tty: link https://www.gnu.org/software/coreutils/manual/coreutils.html#ddstatus'status=LEVELX'tty: link'
-
The LEVEL of information to print to standard error;
'none' suppresses everything but error messages,
'noxfer' suppresses the final transfer statistics,
'progress' shows periodic transfer statistics
N 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, R, Q.
Binary prefixes can be used, too: KiB=K, MiB=M, and so on.
If N ends in 'B', it counts bytes not blocks.
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
- sparse
-
try to seek rather than write all-NUL output blocks
- 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
-
Request to drop cache. See also oflag=sync
- 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.
Options are:
- X'tty: link https://www.gnu.org/software/coreutils/dd#d-help'--helpX'tty: link'
-
display this help and exit
- X'tty: link https://www.gnu.org/software/coreutils/dd#d-version'--versionX'tty: link'
-
output version information and exit
AUTHOR
Written by Paul Rubin, David MacKenzie, and Stuart Kemp.
REPORTING BUGS
Report bugs to:
bug-coreutils@gnu.org
Report Gentoo bugs to: https://bugs.gentoo.org/
GNU coreutils home page: <https://www.gnu.org/software/coreutils/>
General help using GNU software: <https://www.gnu.org/gethelp/>
Report any translation bugs to <https://translationproject.org/team/>
SEE ALSO
Full documentation <
https://www.gnu.org/software/coreutils/dd>
or available locally via: info aq(coreutils) dd invocationaq
Packaged by Gentoo (9.10 (p0))
Copyright © 2026 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://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.
Index
- NAME
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- SYNOPSIS
-
- DESCRIPTION
-
- AUTHOR
-
- REPORTING BUGS
-
- SEE ALSO
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