An Interview with Jeff Dike - The creator of User Mode Linux

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Jeff Dike is the creator and maintainer of User Mode Linux (UML) - a virtual machine which runs on Linux. In recent times, UML has gained a lot of significance after Linus Torvalds incorporated the UML patch into the official Linux kernel source tree. Now a days Jeff works full time for Intel devoting his time towards further development of UML. He has also authored a book titled "User Mode Linux" published by Prentice Hall. After reading through the book written by him on this subject and also running UML on my machine, I had the desire to ask him a few questions on UML and how it fared when compared with other virtualization technologies. And Jeff very kindly agreed to take time off from his important work schedule to give answers to my queries. Without further ado here are the questions I posed to Jeff Dike along with his replies.

Question: There are a lot of virtualization technologies like VMware, Xen and QEMU other than UML. What are the relative strengths of UML which would urge a person in choosing it over its counterparts ?

Jeff Dike: The reason varies according to the technology that you're comparing UML to. With qemu and other instruction emulators, the attraction is speed. These let you boot a kernel on a machine with a different architecture, i.e. a ppc kernel on an i386 host. When the architecture of the virtual machine is the same as the host, there are few reasons to take the overhead of instruction emulation, even if the emulator is optimized in this case to just virtualize instructions.

Full Interview.