To the person that said linux is not unix-based: Not sure what you're thinking, but linux is definitely of the unix family. Linus Torvalds consulted "The Design of the Unix Operating System" by Maurice J Bach while writing the early linux kernel, and any seasoned unix user that logs into a linux box immediately says, "Hey, this is unix".
Legally, linux can't be called "UNIX (TM)" thus the cute recursive motto "gnu's not unix" but neither can bsd legally be called "UNIX (TM)".
Clearly, however, both linux and bsd are "unix", technically speaking. »