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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 (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' sup- presses 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 statis- tics 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 (C) 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' GNU coreutils 9.9 November 2025 DD(1)
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