Want to test a new Linux distro but you do not want to mess up with your existing installation? Want to test the latest and greatest linux kernel before it is released but do not have a spare computer to install it on? Yeah, Live CDs rock but an installed Linux is still better - so how do you do it without spending money on commercial virtualization solutions?

User Mode Linux (UML) to the rescue. Here's another guide on how to run multiple Linux operating systems on a host computer also running Linux and without spending a single cent on solutions like VMWare and Parallels.

UML allows you to create completely independent virtual machines that run isolated from each other, complete with their own Linux kernels. You could use UML to increase security by completely isolating server processes from each other and from the physical machine. Or you could use it to mimic other development or production environments, even giving users root access to the virtual machine. You could also use it to try out new software without having to worry about it wrecking your system.

I have tried Xen before and it works wonders provided that you have sufficient resources, i.e. RAM. With processors providing hardware virtualization and RAM becoming more affordable, guest OS performance will improve considerably.

Why not give it a try and see for yourself?