I'm a Unix beginner but I want to change that. I'm already familiar with Ubuntu, a bit with some other distros for linux, windows and a little bit with mac. So the first thing I did was searching how to install unix and found something called FreeBSD. Is that the only free unix? So where can I start?
closed as not a real question by derobert, vonbrand, jasonwryan, Gilles, rahmu Apr 10 '13 at 12:40
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There isn't a single Unix, the vendors made sure of that in the '80s. The closest thing to a modern Unix that is freely available would be Solaris, e.g. as in Illumnos. From an early fork in the Unix lineage come the various BSD systems.
For all intents and purposes, a Linux distribution (like Ubuntu) is (a form of) Unix. It can't call itself that, there are usage restrictions on the name, but Linux (the kernel) provides (most of) the interface to the kernel expected in such a system, and a motley collection of software (much provided by the GNU project, but there are many other contributors) provides a very good approximation to what the relevant standards (notably POSIX) specify. A Linux distribution like Ubuntu combines the kernel and userland into a working system. Just stick to Ubuntu (or whatever other Linux distribution floats your boat, or one of the BSDs), and learn how to use that well.
Although they can't call a GNU/Linux-system "Unix", it's close enough for most purposes. The important difference is that it cost lots of money to be certified as "Unix".
Short history lesson: When UNIX was invented in a lab at AT&T, they were not allowed to sell it commercially, so they gave it away to several schools - including Berkley and Stanford. These schools used this to make their own version of UNIX - BSD at Berkley and SUN (yes that SUN) at Stanford. Later AT&T's UNIX went commercial, and to avoid problems, BSD and SUN rewrote their code. Other companies - like IBM (with AIX), HP (with HP-UX) and Microsoft - also made their own Unix-versions. These were all collectively known as Unix or plural Unices.
For BSD funding for the project ended, and they released the source-code of their final version to the public. This lead to project like FreeBSD, OpenBSD and NetBSD - as well as other, like DragonflyBSD.
SUN's Unix became known as "Solaris", and they eventually released an open-source version called OpenSolaris. When this ended, a fork was made by the Illumnos-project called OpenIndiana (a good alternative to Solaris). You can actually download Solaris, but upgrades and support will be limited if you don't fork-out lots of $$$ for support.
Other interesting project are Haiku and Minix, but they're as much "clones" and not "real Unix" as Linux.
While it's fun to try *BSD and Solaris (especially Solaris have some rather cool features), I recommend sticking to Linux. Linux is in high demand. Try submerging yourself in the details; learn the system and look at the config-files (and not just use GUI-tools and automatic). Try the distros Slackware, Gentoo or LinuxFromScratch, if Ubuntu isn't challenging enough and you really want to know how linux works from the ground up.
The thing is that for daily use, there are very little difference between Linux (with it's various distros) and "real" Unices like Solaris and *BSD. If you start looking at administrating the system and administration tools, there may be lots differences - but these variations are almost as great between various "Real Unix"-systmes (e.g. between Solaris, HP-UX and AIX), as they are between "Real Unix"-systems and Linux-distros... actually, when it comes to administration and package-handling, there are quite a lot of differences between different Linux-distros too. Remember that most Unix-users (in large companies and such) only run applications (e.g. spreadsheets and editors) and do simple file-manipulation, while a few experts administer the system to keep it healthy. It's only when you install Unix/Linux "at home" for personal use; you must take on the double-role of being not only a "normal" user, but also being an administrator.
So if you know how to use the shell, normal commands and applications under Linux; then you know how to do it under any "Real Unix" system too - the commands are (more or less) the same... And when it comes to system administration, you must in any case learn to use the tools for whatever particular Unix-system or Linux-distro you actually end-up administrating, because these tools varies too much between systems anyway. Of course, that doesn't prevent you from learning how to be a good administrator on one system, and applying the lessons on another - even if you may have to use a completely different set of admin-commands to do it.