Linux and Unix

This might seem like a stupid question but whats the difference between Linux and Unix.

Hmmmm... that's kind of a hard question. This is a bit of an oversimplification, but here goes.....

There really is no one "Unix." Unix really refers not to one operating system, but rather to a broad family of operating systems descended from the original AT&T Unix developed in 1969. They all share certain common attributes and are all descended from a common code base, but the Unix family tree is quite diverse. Examples of true Unix include IRIX, AIX, HP-UX, Solaris, SCO Unix, and many others.

Linux is not Unix in the sense that it is not directly descended from the Unix family and doesn't share a common code base with them. It was written from scratch in 1991 to look like Unix and act like Unix, but it isn't Unix. It doesn't have the pedigree of Unix, basically. It's kind of like the adopted child of the family. :D

Linux is properly referred to as a Unix-like operating system, although you will often see them grouped together under the abbreviation *nix. As a practical matter, Linux is a Unix in the sense that if it looks like a duck, walks like a duck, and quacks like a duck, it's a duck. It's really a technical distinction as far as the average user is concerned.

The biggest difference that the average user will see is that Linux is free and open-source, while the Unixes, with the exception of the BSDs, are very expensive and proprietary.

If you have the stomach for it, you can see the family tree at http://www.ehlis.com/adam/solaris/history.html

All the gory details of Unix history are at http://www.dei.isep.ipp.pt/docs/unix.html.

Thanks.