Dd (Unix)

dd is shell command for reading, writing and converting file data. Originally developed for Unix, it has been implemented on many other environments including Unix-like operating systems, Windows, Plan 9 and Inferno.^[1]

The command can be used for many purposes. For relatively simple copying operations, it tends to be slower than domain-specific alternatives, but it excels at overwriting or truncating a file at any point or seeking in a file.^[2]

The command supports reading and writing files, and if a driver is available to support file-like access, the command can access devices too. Such access is typically supported on Unix-based systems that provide file-like access to devices (such as storage) and special device files (such as /dev/zero and /dev/random). Therefore, the command can be used for tasks such as backing up the boot sector of a drive, and obtaining random data.

The command can also support converting data while copying; including byte order swapping and converting between ASCII and EBCDIC text encodings.^[3]

dd is sometimes humorously called "Disk Destroyer", due to its drive-erasing capabilities involving typos.^[4]