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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/>
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