How do I find out the kernel version I am running?

Well there are multiple ways to find the kernel version

Open terminal and execute:

uname -r

It would display something like:

3.8.0-30-generic

You can get further information on the current kernel with

uname -a

It would display something like:

Linux saurav-P4I45Gx-PE 3.8.0-30-generic #44~precise1-Ubuntu SMP Fri Aug 23 17:33:45 UTC 2013 i686 i686 i386 GNU/Linux

Another way to know the kernel version is to open Synaptic Package Manager and search for linux image. You have to check for the installed Kernel version.

Another way to find version of installed kernels is to run this command:

dpkg -l | grep linux-image | grep ii

or for just the version strings:

dpkg -l | grep linux-image | grep ii | awk '{print $3}'

The latest kernel (the one with the highest version number) will boot by default, so if you have rebooted since the last kernel update, and you have not made adjustments to boot into a kernel other than the default, then you can be reasonably confident that the highest version number displayed will be the version of the running kernel, but you should use uname for more reliable information.

uname -a and uname -r will give you the information of the kernel used.

The official version of an Ubuntu kernel is found in the /proc/version_signature file (mainline kernels may lack this file, in which case uname -r is sufficient).

This file contains both the full Ubuntu version of the kernel and the mainline version on which it is based. The first field is always Ubuntu, the second field is the Ubuntu kernel version, and the final field is the upstream version:

$ cat /proc/version_signature
Ubuntu 2.6.35-6.9-generic 2.6.35-rc3

This and many questions just like it are answered in Ubuntu Kernel Team's wiki specifically the FAQ.