Dd (Unix)

dd (Data(set) Definition) is a shellcommand for reading, writing and converting filedata. Originally developed for Unix, it has been implemented on many other environments including Unix-likeoperating systems, Windows, Plan 9 and Inferno.

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.

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.

dd is sometimes humorously called "Disk Destroyer", due to its disk-erasing capabilities involving typos.