| Many system services can best be implemented within a virtual machine monitor (VMM) instead of a traditional operating system. Unfortunately, traditional VMMs have targeted a single application (time-sharing), and do not support the graceful incorporation of new system services.;This dissertation describes muDenali, a VMM that supports new services by making extensibility a first class goal. Using a technique called hardware interposition, muDenali allows service authors to modify the implementation of hardware components such as virtual disks. On top of this basic mechanism, muDenali supplies a user-mode interposition library, which exposes extensibility through a set of C-based interfaces.;To evaluate muDenali I have developed a range of virtual machine services, including migration and intrusion detection. The most significant new service, the Chronus tool, serves as a "debugger" for system administration errors. I provide evidence that muDenali substantially simplifies the development of such services. I also provide quantitative results demonstrating that the overhead of muDenali is tolerable in the majority of situations. |
