DD(1)

📦
version 9.12 · 28 versions
, in arch rolling

💖 DD(1) — convert and copy a file, bestie edition 🦋

okay so you asked about dd and I am SO glad you did, because this little command is lowkey the main character of Unix. it's from GNU coreutils, it's a whole manual page, and we're gonna go through every single bit of it together. no skipping, no skimming, periodt. 💅

✨ NAME ✨

dd — convert and copy a file 🎀

🌸 SYNOPSIS 🌸

dd [OPERAND]...
dd OPTION

💜 DESCRIPTION 💜

So the whole vibe is: copy a file, converting and formatting according to the operands. That's it. That's the assignment. But bestie, the operands are where the drama lives, so let's go.

  • bs=BYTES — read and write up to BYTES bytes at a time (default: 512); this one overrides ibs and obs, she does not share the spotlight 💅
  • 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

okay now the numbers, because N and BYTES are not just gonna take any old digits, they want the cute suffixes too:

N and BYTES may be followed by these 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, bestie: KiB=K, MiB=M, and so on. And here's the plot twist — if N ends in 'B', it counts bytes not blocks. iykyk. 🧚

🎀 CONV symbols, one by one 🎀

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

🌈 FLAG symbols, also one by one 🌈

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 — request to drop cache. See also oflag=sync
  • noctty — do not assign controlling terminal from file
  • nofollow — do not follow symlinks

Sending a USR1 signal to a running 'dd' process makes it print I/O statistics to standard error and then resume copying. yes bestie, you can just poke her mid-copy and she'll tell you how it's going. iconic behavior honestly. 🫶

⭐ Options are: ⭐

  • --help — display this help and exit
  • --version — output version information and exit

👑 AUTHOR 👑

Written by Paul Rubin, David MacKenzie, and Stuart Kemp. legends, all three. 🎀

🙈 REPORTING BUGS 🙈

Found a bug? Tell the girlies:

Copyright © 2026 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. fr fr, not even a little one. 😭

🌟 SEE ALSO 🌟

and that's the whole page, bestie! 🦋✨ this was GNU coreutils version 9.12, dated September 2026 — go forth and copy responsibly, mwah 💖💅🍓

📦 where this page comes from