First, you'll need to understand the history. Most Unix people know the story of Kenneth Thompson and Dennis Ritchie and how they started Unix around the time that we first traveled to the moon. They were trying to get some game-type software ported to a different platform and came up with Unix, a pun on an operating system called Multics.
Evenutally, AT&T took over the rights. Then, the old System V versus Berkeley wars occurred, and Novell entered the mix, interestingly enough. Finally, today the license is owned by Caldera, who purchased SCO Unix a while ago. (You may want to read SearchEnterpriseLinux.com's articles on SCO's lawsuit against IBM. It's very interesting.)
Linux's evolution comes from a different species. In 1991, Linus Torvalds began writing a kernel, which he named "Linux." The kernel itself is a freely modifiable one. In the beginning, it was placed under the General Public License (GPL) umbrella, making it possible to distribute and use Linux free of charge. Developers have access to all the source code and are able to integrate new functions very easily and eliminate programming bugs quickly. Also, new drivers can be developed much more quickly than in the Unix arena.
The bottom line: Linux is not Unix because it was not derived itself from the original System V code. Instead, it was derived from scratch essentially, but it contains Unix-like features and commands.
The many Linux variants out there, including Red-Hat and Caldera all build on the Linux kernel while offering various other utilities that they claim make their own variant a better one.
Regarding features and functionality, though Linux itself is becoming much more scalable and reliable, it is generally not widely used in the corporate world (yet) as much for enterprise wide mission critical database applications. Linux got to where it is today by being the platform of choice for the Internet (Web and e-mail servers). It has received a lot of support recently from the big database vendors, such as IBM (DB2 & Informix) and Oracle. These big vendors' customers frequently want to migrate from Unix to Linux because of flexibility and cost issues.
Linux is also starting to make waves as a desktop alternative to Windows. That's something the Unix kings (IBM, SUN, HP) could never really accomplish, mostly because of their own competitiveness with each other. As an OS, Linux probably has as many similarities and differences to Unix as any Unix variant has to another. An AIX administrator cannot succeed at a high level after being exposed to Solaris for only a few days. He or she will know some stuff, though. Pretty much, you can expect the same here with respect to Linux. So, I would recommend a Linux course for Unix adminstrators to Unix people to get up to speed. A general introductoryLinux course will probably be too boring for you. Here's one such course.
This was first published in May 2003