The version of unix running on hewlett-packard workstations.

HP-UX conforms to x/open's Portability Guide Issue 4 (xpg4), Federal Information Processing Specification (FIPS) 151.1, posix 1003.1, POSIX 1003.2, at&t's System V Interface Definition 2 (svid 2). HP-UX incorporates selected features from the University of California at Berkeley Software Distribution 4.3 (4.3bsd).

It is known by some as "hp-sux".