dd(1) User Commands dd(1)
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 up to BYTES bytes at a time (default: 512);
overrides ibs and obs
cbs=BYTES
convert BYTES bytes at a time
conv=CONVS
convert the file as per the comma separated symbol list
count=N
copy only N input blocks
ibs=BYTES
read up to BYTES bytes at a time (default: 512)
if=FILE
read from FILE instead of standard input
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 standard output
oflag=FLAGS
write as per the comma separated symbol list
seek=N (or oseek=N) skip N obs sized output blocks
skip=N (or iseek=N) skip N ibs sized input blocks
status=LEVEL
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)
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
noctty do not assign controlling terminal from file
nofollow
do not follow symlinks
Sending a INFO signal to a running 'dd' process makes it print I/O
statistics to standard error and then resume copying.
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 bugs to: bug-coreutils@gnu.org
GNU coreutils home page: <https://www.gnu.org/software/coreutils/">https://www.gnu.org/software/coreutils/>
General help using GNU software: <https://www.gnu.org/gethelp/">https://www.gnu.org/gethelp/>
Report any translation bugs to <https://translationproject.org/team/">https://translationproject.org/team/>
COPYRIGHT
Copyright © 2026 Free Software Foundation, Inc. License GPLv3+: GNU
GPL version 3 or later <https://gnu.org/licenses/gpl.html">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.
SEE ALSO
Full documentation <https://www.gnu.org/software/coreutils/dd">https://www.gnu.org/software/coreutils/dd>
or available locally via: info '(coreutils) dd invocation'
GNU coreutils 9.10 March 2026 dd(1)
coreutils 9.10 - Generated Thu Apr 2 07:30:02 CDT 2026