Howto: Linux and Windows virtualization with KVM and Qemu. In the wise words of Wikipedia, . Within this definition sits a whole variety of products - Sun's Virtual. Box, Parallels, Bochs, Xen, KVM, Qemu, various flavours of VMware and many others.

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And there's a great deal of jargon to confuse the unwary - emulation, full virtualisation, paravirtualisation, virtual appliance, hypervisor.. And not everyone agrees exactly what all these terms actually mean. We're going to deliberately sidestep the jargon and the hype to take a practical look at the virtualisation technologies in Ubuntu, in particular KVM and Qemu and the related userspace tools that create and manage virtual machines. Although the discussion centres on Ubuntu, the technology is applicable to all Linux distros.

Warning: if you're a little less experienced (or a little more time constrained!) you might find our other article, virtualisation made easy, a little easier to read. The diagram below is an attempt to show how some of the virtualisation components in Linux relate. The lower part of the diagram shows the underlying technologies.

On the left, Xen is a software layer that conceptually sits below the operating system. It's called a hypervisor, and it's the first thing that gets to run (after the bootloader) at boot time. Xen creates a single virtual machine (called Domain 0 or Dom 0 for short) that runs Linux. It's this domain that provides Xen with its virtualised resources. Additional user domains (Called Dom U) can later be created to run additional instances of Linux.

Although we won't discuss it further here, Xen is a stable, industrial- strength virtualisation solution. Canonical is using it, for example, to host the virtual Ubuntu machines that students use for hands- on work in their new server course. Some of the key pieces of the virtualisation jigsaw puzzle, and (approximately) how they fit together, with libvirt right in the middle. KVM (not the keyboard switcher)The middle component of the diagram shows KVM (it stands for Kernel Virtual Machine).

• A hypervisor or virtual machine monitor (VMM) is computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs.
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KVM provides full virtualisation and can run unmodified Linux or Windows images, but it requires CPU virtualisation extensions (Intel VT or AMD- V). It consists of a loadable kernel module (kvm. These kernel components are included in the mainline kernel as from version 2.

KVM is used in conjunction with Qemu to emulate other hardware such as the network card, hard disk, graphics adapter, and so on. It's this combination that we'll focus on here. On the right of the diagram we see Qemu functioning as a userspace, software- only emulation package. Current Affairs Updates Via Sms Opinie. It can be used standalone (that is, it does not require a special kernel module, or CPU virtualisation extensions, or a hypervisor layer) and is capable of running unmodified operating system images. Used standalone, Qemu is not the fastest emulation solution; however, it can be accelerated by using KVM, if it's present, or by the kqemu kernel module. The top part of the diagram shows a few of the userspace tools. Virsh is a command- line tool for management of virtual machines.

It can be used to start, shut down, pause, resume, suspend and restore virtual machines, and to list the currently running machines. It can arrange for VMs to start automatically when the host machine boots, or even to migrate VMs to a different host. Virt- viewer is a minimal tool for displaying the graphical console of a virtual machine. The console is accessed using the VNC protocol. Virt- manager is a desktop tool (written in Python) for managing virtual machines. It provides the ability to control the life cycle of existing machines (bootup/shutdown, pause/resume, suspend/restore), provision new virtual machines, manage virtual networks, access the graphical console of virtual machines and view performance statistics.

All of these tools are heavily dependent on libvirt, a C library for interfacing with the underlying virtual machines. Libvirt is the true hero of our story. It provides a stable, consistent API for machine management across a variety of virtualisation technologies. Currently it supports Xen, Qemu, KVM, User Mode Linux and Virtual. Box, among others. Libvirt uses XML- based config files under /etc/libvirt and /var/lib/libvirt to define the virtualised hardware. Libvirt is also used by the libvirtd daemon, used to mediate communication with the virtualisation system.

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Time for some action In this tutorial we'll build three KVM- based virtual machines. On the first we'll install Vista from standard installation media. On the second we'll install Red Hat Linux from an ISO image, and the third will install Ubuntu direct from the repositories. But first, this: KVM requires virtualisation support in your CPU.

That is, it requires Intel- VT or AMD- V processor extensions. To see if your processor supports one of these, run the command. Otherwise, it does - but you still need to make sure that virtualisation is enabled in the BIOS. Now that we've got this caveat out of the way we're going to use virt- manager to build a KVM/Qemu VM running Vista. To begin creating a new VM, right- click on the 'localhost' line in the virt- manager main window and select New from the menu. You'll be taken through a series of information- gathering screens, some of which are shown in the walkthrough, below. The result of this process is an XML file describing the VM's settings (/etc/libvirt/qemu/vista.

VM's filesystem. Virt- manager will automatically boot the newly created VM and begin installation of the operating system from the selected media. Step by step: Build a virtual Vista install. Choose the source: When you've started the virtual machine creation wizard you'll be asked to choose your installation source. In this case we're installing from a physical Vista DVD. Make virtual partitions: If you have an ISO image to install from, say so here. Otherwise, use the hosts's CD.

The virtual disk can be one of the host's physical partitions, or an image file within the host's filesystem. Allocate RAM: Specify the initial and maximum amount of memory to allocate to the VM, review your choices, then bask in the end product - Vista running within a Qemu/KVM virtual machine. You can also build VM images from the command line using virt- install. We built our second VM and installed Red Hat from an ISO image with the following command.

RHEL5 - -ram 1. 00. RHEL5. img,size=8 - -network network: default.

RHEL5. 2- x. 86. The system installed and rebooted uneventfully. For the third VM, and as an alternative to creating an empty virtual machine and then installing an OS into it, we used VMBuilder, a Python script that can construct a VM image from scratch by downloading all the pieces from the Ubuntu repositories on the fly. It's a rewrite of the shell script ubuntu- vm- builder, which was in Ubuntu 8.

LTS. Both were written by S. Here's an example. The only two essential parameters are the first two. Here, kvm specifies the hypervisor (ie the virtualisation technology that the image is intended to work with).

Supported values are esxi, xen, kvm, vmw. The second parameter, ubuntu specifies the distro you want to build; Ubuntu is currently the only one supported. The time taken to provision a VM in this way will depend heavily on the bandwidth between you and the repositories. If you're planning to install several similar VMs you should consider creating a proxy repository server. This can be as easy as choosing a machine on your network and installing the package apt- proxy. This will create a caching APT proxy that listens on port 9. You'll need to add a - -mirror option to your VMBuilder command line to direct it to the proxy, like this.

You won't see any speed improvement for the first VM you build, because the proxy will need to populate its cache from the back- end repositories, but subsequent builds should go much faster (on a simple test, the build time for the command shown above dropped from 4 minutes 3.