"User-mode Linux (UML) is the port of Linux that runs inside Linux. This provides a virtual Linux machine running on the physical Linux host. This is interesting from a purely technical standpoint, since it demonstrates that the Linux system call interface is complete enough to be self-hosting. It is also very interesting from a practical point of view, as it lends itself to a surprisingly wide variety of applications.
"UML can run essentially anything that will run on the host (the exceptions mainly being things that deal directly with hardware). This means that a UML can do anything that a physical Linux machine can, with the advantage that UMLs can be created and destroyed as needed. The fact that a UML instance is virtual gives it capabilities which make even more applications possible.
"Many of these applications are common to any virtual machine technology which can boot a Linux kernel, while others are due to the unique design of UML..."
