DD

Section: User Commands (1)
Updated: December 2009
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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.

bs=BYTES: read and write BYTES bytes at a time (also see ibs=,obs=)
cbs=BYTES: convert BYTES bytes at a time
conv=CONVS: convert the file as per the comma separated symbol list
count=BLOCKS: copy only BLOCKS input blocks
ibs=BYTES: read 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=BLOCKS: skip BLOCKS obs-sized blocks at start of output
skip=BLOCKS: skip BLOCKS ibs-sized blocks at start of input
status=noxfer: suppress transfer statistics

BLOCKS 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.

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
nocreat: do not create the output file
excl: fail if the output file already exists
notrunc: do not truncate the output file
ucase: change lower case to upper case
swab: swap every pair of input bytes
noerror: continue after read errors
sync: pad every input block with NULs to ibs-size; when used with block or unblock, pad with spaces rather than NULs
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
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.

: $ dd if=/dev/zero of=/dev/null& pid=$!
$ kill -USR1 $pid; sleep 1; kill $pid
: 18335302+0 records in 18335302+0 records out 9387674624 bytes (9.4 GB) copied, 34.6279 seconds, 271 MB/s

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 dd bugs to bug-coreutils@gnu.org
GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
General help using GNU software: <http://www.gnu.org/gethelp/>

COPYRIGHT

Copyright © 2009 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://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.