What Is UML?

User Mode Linux (UML) is a virtual Linux machine that runs on Linux. Technically, UML is a port of Linux to Linux. Linux has been ported to many different processors, including the ubiquitous x86, Sun's SPARC, IBM and Motorola's PowerPC, DEC's (then Compaq's and HP's) Alpha, and a variety of others. UML is a port of Linux in exactly the same sense as these. The difference is that it is a port to the software interface defined by Linux rather than the hardware interface defined by the processor and the rest of the physical computer.

UML has manifold uses for system administrators, users, and developers. UML virtual machines are useful for test environments that can be set up quickly and thrown away when no longer needed, production environments that efficiently use the available hardware, development setups that can make it much more convenient to test software, plus a surprising number of other things.