dd(1) — Linux manual pages

Linux manual pages	Section 1: General Commands

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

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/>

Report dd translation bugs to <http://translationproject.org/team/>

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