Fix: Ubuntu not able to use installed memory

To check how much memory ubuntu is able to use on your system, run the following command in a terminal:

free -m

For reference, I know that my PC has 4GB of physical memory installed and the result of the command above shows:

             total       used       free     shared    buffers     cached
Mem:          4012       1837       2175          0        451        722
-/+ buffers/cache:        662       3349
Swap:         9538          0       9538

If you have more than 3GB of physical memory installed and if you haven't specifically enabled PAE for your ubuntu desktop installation then I'm betting that the total Mem you'll be seeing is LESS than the actual physical memory installed in your machine. To fix this, you simply have to install a PAE enabled kernel. Run the following commands in a terminal:

sudo apt-get update

sudo apt-get install linux-server linux-headers-server linux-image-server

Reboot your system. To check if you have the correct kernel running and all your mem enabled:

uname -a

free -m

You should see an ubuntu server kernel running and the correct amount of memory is available for use. Did it work for you? You are welcome to post your comments/questions or better yet, link to this post, blog about it and tell all your friends who might find this post useful.