Virtualization on the command line with KVM

Virtual machines are just practical. You can use virtual computers to test new distributions, start Windows or revive older operating systems. One of the most popular open source virtualization software tools goes by the somewhat unwieldy name "Kernel-based Virtual Machine" (KVM [1] for short). Although primarily driven by Red Hat, it's the preferred virtualization solution in almost all major distributions.

Division of Labor

KVM consists of several components (Figure 1). The base is the kernel module that ensures that the virtual machine can access the actual hardware efficiently without getting in the way. This kind of a manager is called a hypervisor [2] or virtual machine manager (VMM). As of version 2.6.20, the KVM module is a standard component of the Linux kernel, which makes it a part of every current distribution.

In the "old days," the module services loaded virtualization software and most distributions used QEMU [3]. The program is considerably older then KVM and would build a complete PC, inclusive of processors. Nowadays, QEMU can use the KVM module and, thus, the physical PC's vital hardware components. The result is a considerably faster execution of the operating systems and programs that QEMU launches.

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