*nix tip of the day: what Linux version am I using?

How to tell the Linux distro version you are using? Since Linux is not exactly the whole ecosystem of computer programs that you are using on your desktop/server but rather the kernel that allocates the physical hardware resources for the computer programs that you are running, it would not be syntactically nor technically correct to name the version of your OS by the version of your OS kernel. Who is who? What we call it generically 'Linux' is in fact:

• a kernel (that project started by Linus Torvalds back in '90s and lately supported by a bunch of programmers) - an essential part of OS

• OS programs that run in top of the kernel and which, if are missing, the kernel is just a beautiful but useless piece of furniture.

So the OS is in fact this combination of GNU with Linux added, so called GNU/Linux. If I run the uname command I got the whole version info, like:

rpi-gentoo ~ # uname -a
Linux rpi-gentoo 3.6.11-cutdown+ #17 PREEMPT Mon Feb 18 14:27:02 CET 2013 armv6l ARMv6-compatible processor rev 7 (v6l) BCM2708 GNU/Linux

Also, the full and the correct name would be GNU/Linux. In order to answer the question "what Linux version am I using?" one should look over the version of its Linux distribution. And that piece of information comes from a file that is located on your /etc folder and which might be called: redhat-release, SuSE-release, debian_version, arch-release, gentoo-release, slackware-version, mandriva-release, etc. So basically to tell what version is your Linux distribution one should run this command:

rpi-gentoo ~ # cat /etc/*-release /etc/*/-version 2>/dev/null
Gentoo Base System release 2.1