Unix versus Linux

It's not as weird as you think. Linux (more accuratly, GNU on the Linux kernel) is one of the few UNIX-like operating systems completely written from scratch.

Solaris, BSD, and many other UNIX-variants, were based on the original (the only) UNIX by AT&T. It was a process of evolution. Parts of the UNIX kernel were taken, altered, extended, mutilated, and what not to eventually become something different.

Linus Torvalds started Linux with nothing more than a bare editor screen. Every bit of the Linux kernel was written specifically for the Linux kernel, although almost everything was designed to be compatible with the original UNIX and emulate much of its features.

So it's more like saying "A dog or an Aibo".

Linux is not -- it is written from scratch. As such, there are some areas where Linux has made some real innovations, and some areas where Linux would have done better to have followed BSD's lead (i.e. networking).

This is why you occasionally have snobbery from OpenBSD and FreeBSD fanatics who will claim that they are the "true" Unix and Linux is an upstart invader. It is precisely this attitude which led to Linux's dominance, as the BSD development team wasn't willing to accept pieces of code mailed in from any 13 year old unknown hacker on the net.

Another reason is that Unix™ is a registered trademark of The Open Group, which is, to use their own words, "an international vendor and technology-neutral, not-for-profit consortium." Unix™ is defined by them as an operating system which they have certified as hewing to the Unix 98™ standard. As I doubt that Linus Torvalds or anyone else has bothered seeking such certification, it's actually illegal to refer to Linux as Unix™. However, for all practical purposes, you need not give a shit.