Open Source Digest: User-mode Linux

“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…”

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