What version of CentOS am I running

When you are asked to deal with a server you have not installed, you need to know which version of Linux you are running on it.

If the case is a CentOS server, you may need to know which version of CentOS you are running.

First check out the version of Linux (Kernel you are running)

 uname -r

You should get something like this:

 2.6.18-308.8.2.el5.028stab101.1

Now to know the version of CentOS you are running. Enter this:

 cat /etc/redhat-release

You will get something like this:

 CentOS release 6.3 (Final)

Now you know the version of Linux (Kernel) and the version of CentOS you are running on your server.