|Well, I'm no guru so I could easily be wrong....but in my limited experience, while very similar, they are not "the same" any more than Windows is the same as OS/2 or Mac's OS/X.|
As I understand it, UNIX was developed at Berkley, or maybe just one version of it.....but Linux, was developed by Linus Torvaldson (not sure of the exact spelling) and while based on UNIX, was different enough to be classified as a separate OS.
Every linux flavor I've examined installs the GUI by default. Whereas with the two flavors of UNIX I've examined (Open/FreeBSD) that's not the case.
Linux is more of a "desktop" distro whereas the two UNIX versions I mentioned are more of a "server" distro. Prime example is OpenBSD. Our security guy uses it as our firewall/routers. We have dual, teamed, redundant servers setup running Open and pf. I doubt you could do that with any linux distro "out of the box" as easily as it can be done with OpenBSD.
You know, I recall a time back in the early 90's when Mac included "DOS" on their PC's so you could run DOS app's. That didn't make them DOS based PC's any more than being able to run a UNIX app on a linux box makes Linux into UNIX.
Anyhow, I may be talking out my a** for all I know.........I'm still pretty green on either............I've only just begun getting into *nix the last year or so. But this is how I've understood what I've been taught, and what I've learned on my own. That is to say, that, while they are very similar in many many ways, they are still different OS's.
Feel free to correct me if I'm wrong. I won't take it as an insult and I'm always open to learning something new.