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Thursday, November 4, 2010

Linux HowTo: Virtualization Primer - VM, Xen, KVM

Virtualization    -    abstraction of computer resources to simulate a non-real env (via h/w, s/w or both).

-Some virtualization terms:
        -host os                 - the base host
        -guest os/vm         - the virtual machine
        -hypervisor            - also called virtual machine monitor (vmm)
                                     - the abstraction layer that emulates a virtual set of resources (eg cpu, ram, disk)
        -h/w emulation      - s/w is used to emulate cpu instruction set. so guest vm runs slower than a standalone. eg bochs
        -para virtualization    - s/w based where the guest vm kernel is modified to fit in the host env. speed comparable to a standalone. eg xen
        -full virtualization  - the vm is broken at the host cpu level. guest vm runs without any overhead or modification. eg kvm


-kvm  
        - kernel based vm
        - builtin linux kernel based, ie, it turns the linux kernel into a hypervisor.
        - since various linux distros are based on the common kernel, kvm is compatible to several distros.

-virt-install Command:
        -virt-install is a cmd line tool to create virtual machines.
        -you can install it in this way:
            # yum groupinstall    virtualization        or
            # yum install virt-install

-the virtual machine daemon is libvirtd.
 -eg:      # service libvirtd    start    |  stop    |  status

-To create a vm env:
            # virt-install    --prompt        [it prompts you for responses like vm name, ram, disk etc]

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