dd Man page

DD(1) User Commands DD(1)

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=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 statis‐
tics

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 sug‐
gested)

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 sta‐
tistics 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:
Report dd translation bugs to

COPRYRIGHT

Copyright © 2016 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.

SEE ALSO

Full documentation at:
or available locally via: info ‘(coreutils) dd invocation’

GNU coreutils 8.25 February 2016 DD(1)