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 (default: 512); overrides ibs and obs

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 standard input

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 standard output

oflag=FLAGS
    write as per the comma separated symbol list

seek=N
    (or oseek=N) skip N obs-sized output blocks

skip=N
    (or iseek=N) skip N ibs-sized input blocks

status=LEVEL
    The LEVEL of information to print to standard error; 'none' suppresses everything but error messages, 'noxfer' suppresses the final transfer statistics, 'progress' shows periodic transfer statistics

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, R, Q. Binary prefixes can be used, too: KiB=K, MiB=M, and so on. If N ends in 'B', it counts bytes not blocks.

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 all-NUL output 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

nocache
    Request to drop cache. See also oflag=sync

noctty
    do not assign controlling terminal from file

nofollow
    do not follow symlinks

Sending a INFO signal to a running 'dd' process makes it print I/O statistics 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
Report bugs to: bug-coreutils@gnu.org
GNU coreutils home page: <https://www.gnu.org/software/coreutils/>
General help using GNU software: <https://www.gnu.org/gethelp/>
Report any translation bugs to <https://translationproject.org/team/>

COPYRIGHT
Copyright © 2025 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://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
Full documentation <https://www.gnu.org/software/coreutils/dd>
or available locally via: info '(coreutils) dd invocation'