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→Shared Kernel Virtualization
Shared kernel virtualization (also known as system level or operating system virtualization) takes advantage of the architectural design of Linux and UNIX based operating systems. In order to understand how shared kernel virtualization works it helps to first understand the two main components of Linux or UNIX operating systems. At the core of the operating system is the ''kernel''. The kernel handles all the interactions between the operating system and the physical hardware. The second key component is the ''root filesystem'' which contains all the libraries, files and utilities necessary for the operating system to function. Under shared kernel virtualization the virtual operating systems each have their own ''root filesystem'' but share the kernel of the host operating system. This structure is illustrated in the following architectural diagram:
[[Image:shared_kernel_diagram.jpg|center]]
Virtualization is made possible by the ability of the kernel to dynamically change the current root filesystem (a concept known as chroot) to a different root filesystem without having to reboot the entire system. In simple terms, shared kernel virtualization is an extension of this capability which allows multiple instances of an operating system to run on a single physical host. Perhaps the biggest single draw back of this form of virtualization is the fact that the guest operating systems must be compatible with the version of the kernel which is being shared. It is not, therefore, possible to run Windows as a guest on a Linux system using the shared kernel approach. Nor is it possible for a Linux guest system designed for the 2.6 version of the kernel to share a 2.4 version kernel.
