dd — the Unix raw data copying tool — has been cheerfully obliterating disks since Version 5 Unix in 1974. Its syntax is unique among Unix commands: not dd source destination like any sane tool, but dd if=source of=destination bs=blocksize — a relic of IBM Job Control Language that crept into Unix for reasons now lost to history. The result is a command where transposing if and of doesn’t produce an error; it simply writes your destination disk to your source disk, atomically destroying whatever was there. Sysadmins have taken to calling it “disk destroyer,” and the Unix community has produced more cautionary tales about mistyped dd commands than about almost any other single tool. It remains, nonetheless, irreplaceable.
