Find: UNIX Operating System Release and Version Number

How do I find Unix version and release number using command line options? What version, release, and maintenance level of Unix is running on my system?

You can use the following commands to find out information about Unix operating systems.

uname Command

Type the following command:
$ uname -a
Sample outputs:

SunOS solaris 5.11 snv_151a i86pc i386 i86pc Solaris

This command works with Linux, BSD and other Unix like operating systems:
$ uname -a
Sample outputs:

Linux wks01 2.6.32-5-amd64 #1 SMP Tue Jun 14 09:42:28 UTC 2011 x86_64 GNU/Linux

IBM AIX Unix Specific Command

Type the following command
# oslevel -r