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DD(1) User Commands DD(1)


dd - convert and copy a file


dd [OPERAND]...


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

read and write up to BYTES bytes at a time (default: 512); overrides ibs and obs
convert BYTES bytes at a time
convert the file as per the comma separated symbol list
copy only N input blocks
read up to BYTES bytes at a time (default: 512)
read from FILE instead of stdin
read as per the comma separated symbol list
write BYTES bytes at a time (default: 512)
write to FILE instead of stdout
write as per the comma separated symbol list
(or oseek=N) skip N obs-sized output blocks
(or iseek=N) skip N ibs-sized input blocks
The LEVEL of information to print to stderr; '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:

from ASCII to alternate EBCDIC
pad newline-terminated records with spaces to cbs-size
replace trailing spaces in cbs-size records with newline
change upper case to lower case
change lower case to upper case
try to seek rather than write all-NUL output blocks
swap every pair of input bytes
pad every input block with NULs to ibs-size; when used with block or unblock, pad with spaces rather than NULs
fail if the output file already exists
do not create the output file
do not truncate the output file
continue after read errors
physically write output file data before finishing
likewise, but also write metadata

Each FLAG symbol may be:

append mode (makes sense only for output; conv=notrunc suggested)
use direct I/O for data
fail unless a directory
use synchronized I/O for data
likewise, but also for metadata
accumulate full blocks of input (iflag only)
use non-blocking I/O
do not update access time
Request to drop cache. See also oflag=sync
do not assign controlling terminal from file
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:

display this help and exit
output version information and exit


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


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Copyright © 2023 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.


Full documentation <>
or available locally via: info '(coreutils) dd invocation'

March 2024 GNU coreutils 9.4