man > dd

DD(1) – User Commands

📛 NAME

dd – convert and copy a file

🚀 Quick Reference

Use Case	Command	Description
💾 Backup a disk	dd if=/dev/sda of=/backup/disk.img bs=4M	Reads from source disk and writes to image file
💿 Create bootable USB	dd if=ubuntu.iso of=/dev/sdb bs=1M status=progress	Writes ISO image directly to USB device
🔄 Clone disk	dd if=/dev/sda of=/dev/sdb bs=64K conv=noerror,sync	Copies entire disk, continuing on read errors
🔠 Convert to uppercase	dd if=input.txt of=output.txt conv=ucase	Converts file contents to uppercase
📁 Create zero-filled file	dd if=/dev/zero of=file bs=1M count=10	Creates a 10 MB file filled with zeros
⚡ Benchmark write speed	dd if=/dev/zero of=test bs=1M count=100 oflag=direct	Measures write performance with direct I/O

🔧 SYNOPSIS

dd [OPERAND]...

dd OPTION

📖 DESCRIPTION

Copy a file, converting and formatting according to the operands.

📐 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 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 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. Binary prefixes can be used, too: KiB=K, MiB=M, and so on.

🔄 Conversion Symbols

• 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

🚩 Flags

• 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
• 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.

⚙️ Options

• --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: https://www.gnu.org/software/coreutils/
Report any translation bugs to https://translationproject.org/team/

📄 COPYRIGHT

Copyright © 2020 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'