DD

Section: User Commands (1)
Updated: March 2021
Page Index

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 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=N: skip N obs-sized blocks at start of output
skip=N: skip N ibs-sized blocks at start of input
status=LEVEL: 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. Binary prefixes can be used, too: KiB=K, MiB=M, and so on.

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
count_bytes: treat 'count=N' as a byte count (iflag only)
skip_bytes: treat 'skip=N' as a byte count (iflag only)
seek_bytes: treat 'seek=N' as a byte count (oflag only)

Sending a USR1 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

GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Report any translation bugs to <https://translationproject.org/team/>

COPYRIGHT

Copyright © 2020 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.

DD