Virtualbox is a tool that provides to run multiple OS’s without rebooting your system. You can install any OS using virtualbox. Its a great tool to run another OS within another OS. For example, If you have installed Ubuntu 12.04 and you want to install Ubuntu 11.10. Then you have option that you can install that alongside Ubuntu 12.04. But with this step you have to reboot each time to switch between different OS’s.

But you can install Ubuntu 11.04 within Ubuntu 12.04 using Virtualbox.

Installation steps for Virtualbox:

• Step 1
  wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add –
• Step 2
  sudo sh -c ‘echo “deb http://download.virtualbox.org/virtualbox/debian precise contrib” >> /etc/apt/sources.list’
• Step 3
  sudo apt-get update && sudo apt-get install virtualbox-4.1

Now open dashboard and type virtualbox,

then open that. It looks like below: