Know what version of Linux distro you are on...

This will help you to identify the operating system details, in case, you have got only Shell prompt in any Linux machine.
Here is the command which will let you know, what version and distribution of Linux you are on.

user@localhost:~$ cat /etc/*-release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=8.10 DISTRIB_CODENAME=interpid DISTRIB_DESCRIPTION="Ubuntu 8.10"

In case of BSD, the command given should be

user@localhost:~$ cat /etc/*version RHEL 5.4

Furthermore, if you want to know what is the kernel version and other system information details, this will be the command that will do the job.

user@localhost:~$ uname -a Linux localhost 2.6.31-20-generic #58-Ubuntu SMP Fri Mar 12 04:38:19 UTC 2010 x86_64 GNU/Linux

..............Done!!!