user-mode-linux

 User-Mode Linux is another virtualisation technique for running Virtual Machines under GNU/Linux. User-mode Linux enables multiple virtual Linux kernel-based operating systems to run as a normal application within a host Linux system.  The single processes are separated from each other, which makes it secure to run on the same machine.Disk storage for the User-Mode Linux is entirely contained inside a single file on your physical machine. Running buggy software or experimenting with new Linux kernels or distributions in the virtual machine would not damage your real computer or your main Linux setup.