Fullscreen for Linux guest OS on VirtualBox

There is a common problem that happens while running Linux guest OS on VirtualBox3.1.6 using Mac OS. The problem is: the Linux guest OS is not full screened on PC. To solve this problem, you need to download guest-additions on VirtualBox website. Download the guest-additions given your version of VirtualBox from this link:

download.virtualbox.org/virtualbox

Install the iso file on the Linux guest OS and restart your guest OS after the installation. Once restarted, go to System->Preferences->Monitors. Change the monitor to 9:16. The guest screen now is full sized.