There is a Linux web site that "tracks" the progress of Linux distributions called Distrowatch.
And although the statistics shown at Distrowatch may be "questionable" (as even the webmaster of the web site has said), it's worth having a look at the popularity of the "major" distributions over the last several years.
Linux Commands Training Tips: Understanding the changing "world" of distributions will help you to realize that it's much better to focus on leaving the Linux commands that are common to ALL distributions is much better than learning anything that is specific to just a single version – such as learn the GUI utility programs that work in just a single version.
Distrowatch Statistics for Some of the Major Linux Distributions the Last Several Years:
According to Distrowatch, Mandriva Linux (formerly Mandrake) was # 1 for 2002, 2003 and 2004. And Ubuntu was # 1 for 2005, 2006, 2007 and 2008!
In addition to this, Mandrake Linux (recently renamed to "Mandriva") was # 1 for 2002, 2003, 2004 and # 2 (as Mandriva) in 2005, but has not been in the top three since!
Notice how easily and quickly Linux distributions – even extremely popular distributions – fall out of popularity!
Red Hat Linux was # 2 for 2002 and 2003, but has not appeared in the top three since 2003!
Again, it's important to note that even one of the most popular Linux distros, Red Hat Linux, has gone down dramatically in popularity!
And Gentoo was # 3 in 2002, but has not appeared in the top three since.
Here are the other Linux distribution names that have been # 2 or # 3 since 2002: Gentoo, Knoppix, Fedora, SUSE and openSUSE.
So, as you can see – Linux distributions come – and many soon go!
Linux Commands Training Tips: Mandrake (a minor Linux distribution) was quite popular for a while and was derived from Red Hat Linux (a major distribution) and is almost similar to Red Hat.
Knoppix Linux (a minor Linux distribution) is a "live" distribution that was derived from Debian (a major distribution) and is similar to this version.
Ubuntu Linux is free (in all senses of the word) and has become extremely popular as both a desktop system and server system.