How do I check what kernel version my server is running?

You can check what kernel version your server is running by typing the command below.

[root@localhost:~]# uname -a
Linux localhost.localdomain 2.6.9-42.0.2.ELsmp #1 SMP Wed Aug 23 00:17:26 CDT 2006 i686 athlon i386 GNU/Linux

The number you will looking for normally starts with a 2.6. In this case
localhost.localdomain is running a 2.6.9-42.0.2.ELsmp kernel at this time.