Note: GNU is one of those recursive acronyms that computer scientists love; it stands for GNU's Not Unix. The GNU Project is an effort sponsored by the Free Software Foundation to provide freely available Unix software. See http://www.gnu.org for related information.

Linux was written totally from scratch without using any of the original AT&T UNIX code. (Throughout this site, UNIX refers to the original trademarked UNIX project invented by AT&T. The term Unix is used here as a generic term for other variants of the operating system.)

Because of that (and because the author is a nice guy), Linux is free. You can obtain the source code, modify, sell or give away the software so long as you provide full source code and don't impose any restrictions on what others do with it. Here's a site with good information about where to buy or download Linux: http://www.linux.org/dist/download_info.html