umlsim extends user-mode Linux (UML) with an event-driven simulation engine and other instrumentation needed for deterministically controlling the flow of time as seen by the UML kernel and applications running under it.

umlsim will be useful for a wide range of applications in research and kernel development, including simulations involving the networking code, regression tests, proof of race conditions, validation of configuration scripts, and also performance analysis.

This paper describes the design and implementation of umlsim, gives a brief overview of the scripting language, and shows a real-life usage example.

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