Installing VirtualBox and CentOS 7 on Ubuntu

VirtualBox is a fantastic (and free) open source project from Oracle which allows a user to run other boxes virtually on their current machine without having to create a dual-boot machine. There are other software that compete with VirtualBox, such as Parallels and VMWare. I won't compare and contrast the major three virtualization distributions as there are several sites that do that, written by people who have the comparative experience.

In Ubuntu: