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DD

Section: User Commands (1)
Updated: July 2014
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
read and write up to BYTES bytes at a time
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=WHICH
WHICH info to suppress outputting to stderr; 'noxfer' suppresses transfer stats, 'none' suppresses all

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.

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 the output for NUL input 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
discard cached data
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.

$ 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

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

AUTHOR

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

COPYRIGHT

Copyright © 2014 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.  

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 coreutils aqdd invocationaq

should give you access to the complete manual.


 

Index

NAME
SYNOPSIS
DESCRIPTION
AUTHOR
COPYRIGHT
SEE ALSO


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