OpenBSD was forked from NetBSD which is derived from 4.3BSD-Reno, and like all BSD, ultimately derives from Research UNIX. The original Berkley Software Distrib

OpenBSD was forked from NetBSD which is derived from 4.3BSD-Reno, and like all BSD, ultimately derives from Research UNIX. The original Berkley Software Distributions all referred to themselves as Unix and upon logging in a user would see a "Welcome to BSD Unix" text banner. Linux derives from Minix which, beyond using a BSD userland, is otherwise unsourced from and unrelated to BSD and UNIX. GNU is a recursive acronym that literally means "GNU's Not Unix!"