Here is a guide that will show you how to install VirtualBox on Ubuntu 12.04. VirtualBox is a cross-platform virtualization application. What does that mean? For one thing, it installs on your existing Intel or AMD-based computers, whether they are running Windows, Mac, Linux or Solaris operating systems. Secondly, it extends the capabilities of your existing computer so that it can run multiple operating systems (inside multiple virtual machines) at the same time. Read more about VirtualBox.
To install VirtualBox on Ubuntu 12.04 open a terminal window (press Ctrl+Alt+T) and copy+paste the following line:
gksudo gedit /etc/apt/sources.list
When your sources.list is open copy+paste the following line:
deb http://download.virtualbox.org/virtualbox/debian precise contrib
When done save and exit the file.
Now you need to install the PGP key, to do this copy+paste the following line:
wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add -
When the GPG key is added you need to update your sources list with the following line:
sudo apt-get update
And to install virtualbox copy+paste the following line:
sudo apt-get install virtualbox-4.1
When VirtualBox is installed you need to install the guest additions copy+paste the following lines.
sudo apt-get install virtualbox-ose-guest-utils
You can install the guest additions after setting up a virtual machine. When a virtual machine is running click on Devices -> Install guest additions and follow the on screen instructions.
Now all there is to do is to download and install the VirtualBox 4.1.12 Oracle VM VirtualBox Extension Pack. Just click on the link to download it and when downloaded install it using VirtualBox.
Download VirtualBox 4.1.12 Extension Pack for All platforms
To start VirtualBox open press the SuperKey and type: virtualbox