VirtualBox is currently one of the most reliable x86 and AMD64/Intel64 virtualization software that combines a considerate number of features and performance. It allows to install various operating systems under Windows, Mac, Linux, and Solaris hosts.
If you want to install VirtualBox on Ubuntu 11.10 or any older versions of Ubuntu, then follow these instructions:
1. Open the terminal and run first this sequence of commands:
sudo add-apt-repository "deb http://download.virtualbox.org/virtualbox/debian oneiric contrib"
wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add -
sudo apt-get update
To start the installation of VirtualBox, run this command:
sudo apt-get install virtualbox
You can then start VirtualBox via the Unity Dash to start the installation of new operating systems under Ubuntu.