DD

Section: User Commands (1)
Updated: March 2007
Index Return to Main Contents
 

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
force ibs=BYTES and obs=BYTES
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
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
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: xM M, c 1, w 2, b 512, kB 1000, K 1024, MB 1000*1000, M 1024*1024, 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)
direct
use direct I/O for data
dsync
use synchronized I/O for data
sync
likewise, but also for metadata
nonblock
use non-blocking I/O
nofollow
do not follow symlinks
noctty
do not assign controlling terminal from file

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 bugs to <bug-coreutils@gnu.org>.  

COPYRIGHT

Copyright © 2006 Free Software Foundation, Inc.
This is free software. You may redistribute copies of it under the terms of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>. There is NO WARRANTY, to the extent permitted by law.  

SEE ALSO

The full documentation for dd is maintained as a Texinfo manual. If the info and dd programs are properly installed at your site, the command
info dd

should give you access to the complete manual.


 

Index

NAME
SYNOPSIS
DESCRIPTION
AUTHOR
REPORTING BUGS
COPYRIGHT
SEE ALSO

linux.jgfs.net manual pages