A host is a system on top of which virtual machines run. Let's see how to prepare a ubuntu server as a virtual machine host.

• Check whether the CPU supports the hardware virtualization:

  egrep '(vmx|svm)' --color=always /proc/cpuinfo
  

• Enable virtualization on the BIOS setup.
• Install KVM and vmbuilder:

  apt-get install ubuntu-virt-server python-vm-builder kvm-pxe
  

• Add the user as which we're currently logged in (root) to the group libvirtd:

  adduser `id -un` libvirtd
  adduser `id -un` kvm
  

• Check whether KVM has successfully been installed:

  virsh -c qemu:///system list
  

  It should display something like this:

  root@server1:~# virsh -c qemu:///system list
  Id Name                 State
  ----------------------------------
  
  root@server1:~#
  

Referencies:

• http://www.howtoforge.com/virtualization-with-kvm-on-ubuntu-11.10

The bridge interface on the host system allows the virtual machines to access the local network (LAN) directly and independently from the host machine, as if they were real machines.

• First install the bridge utils:

  apt-get install bridge-utils
  

• Then add a bridge interface br0 at /etc/network/interfaces

  auto lo
  iface lo inet loopback
  
  auto br0
  iface br0 inet static
  address 192.168.1.10
  netmask 255.255.255.0
  gateway 192.168.1.1
  bridge_ports eth0
  bridge_fd 9
  bridge_hello 2
  bridge_maxage 12
  bridge_stp off
  

• Finally restart the networking:

  sudo /etc/init.d/networking restart
  

Referencies:

• https://help.ubuntu.com/11.10/serverguide/C/network-configuration.html#bridging
• http://www.howtoforge.com/virtualization-with-kvm-on-ubuntu-11.10

• Create a directory for the virtual machine on /var/lib/libvirt/images/:

  cd /var/lib/libvirt/images/
  mkdir ns1
  cd ns1/
  

• We will use the vmbuilder tool to create VMs, which uses a template to create virtual machines. This template is located in the /etc/vmbuilder/libvirt/ directory and we make a copy of it:

  mkdir -p mytemplates/libvirt
  cp /etc/vmbuilder/libvirt/* mytemplates/libvirt/
  

• Define the partitions in the file vmbuilder.partition with a content like this:

  root 1000
  swap 500
  

• Create a script called boot.sh that will be executed when the VM is booted for the first time:

  # This script will run the first time the virtual machine boots
  # It is ran as root.
  
  # Expire the user account
  passwd -e citadmin
  
  # Install openssh-server
  apt-get update
  apt-get install -qqy --force-yes openssh-server
  

• Create the script install.sh with a content like this:

  #!/bin/bash
  
      # --mirror=http://192.168.1.249/apt-mirror/archive.ubuntu.com/ubuntu \
  vmbuilder kvm ubuntu --suite=oneiric --flavour=virtual --arch=amd64 \
      --iso=/data/iso/ubuntu-11.10-server-amd64.iso \
      -o --libvirt=qemu:///system \
      --ip=192.168.1.252 --gw=192.168.1.1 \
      --part=vmbuilder.partition --templates=mytemplates \
      --user=citadmin --name=CITAdmin --pass=CITAdmin \
      --addpkg=vim-nox --addpkg=acpid \
      --firstboot=/var/lib/libvirt/images/ns1/boot.sh \
      --mem=256 --hostname=ns1 --bridge=br0
  

• Run install.sh and do the installation. The disk images will be located in the ubuntu-kvm/ subdirectory of our VM directory

  ls -l /var/lib/libvirt/images/ns1/ubuntu-kvm/
  

• Move the created disk image to the directory /images/:

  mkdir -p /images/
  mv ubuntu-kvm/tmpRwPa27.qcow2 /images/ns1.qcow2
  

• Edit the file /etc/libvirt/qemu/ns1.xml and modify the path of the image, so that it looks like this:

  <disk type='file' device='disk'>
    <driver name='qemu' type='qcow2'/>
    <source file='/images/ns1.qcow2'/>
    <target dev='hda' bus='ide'/>
    <address type='drive' controller='0' bus='0' unit='0'/>
  </disk>
  

• Redefine the virtual machine:

  virsh define /etc/libvirt/qemu/ns1.xml
  

Whenever the configuration of a virtual machine changes, it should be redefined (which means updating the registry of virtual machines with the latest configurations):

virsh define /etc/libvirt/qemu/vm1.xml
virsh list --all
virsh start vm1

The program virt-manager is a desktop (GUI) application, based on libvirt, which can be used to manage virtual machines even on remote hosts (through ssh). Let's see how to install and use it.

• Install the virtualization packages:

  sudo apt-get install qemu-kvm libvirt-bin virt-manager bridge-utils
  

• Check that it is OK:

  kvm-ok
  sudo kvm-ok
  

• Manage local and remote virtual hosts:

  virsh -c qemu:///system list
  virsh -c qemu+ssh://admin@192.168.10.50/system list
  virt-manager -c qemu:///system 127.0.0.1
  virt-manager -c qemu+ssh://admin@192.168.10.50/system
  

Referencies:

• http://www.itworld.com/virtualization/216949/crash-course-virtualization-kvm-ubuntu-server?page=0,1

The format qcow2 has some advantages with respect to the raw format. For example it can be compressed, it can have snapshots, etc.

• Use qemu-img convert like this:

  cd /var/lib/libvirt/images/
  qemu-img convert -c -O qcow2 vm1.img vm1.qcow2
  

• Modify /etc/libvirt/qemu/vm1.xml like this:

  <disk type='file' device='disk'>
  <driver name='qemu' type='qcow2'/>
     <source file='/var/lib/libvirt/images/vm1.qcow2'/>
     <target dev='vda' bus='virtio'/>
     <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
  </disk>
  

A virtual machine built with VMWare can be converted to KVM.

• Install the neccessary packages:

  aptitude install virt-goodies qemu-kvm kvm \
  	 libvirt-bin ubuntu-vm-builder bridge-utils virt-top
  

• Convert the disk image from format vmdk to qcow2:

  qemu-img convert User-PC.vmdk -O qcow2 User-PC.qcow2
  

• Convert the vmx file to format xml:

  vmware2libvirt -f User-PC.vmx > User-PC.xml
  

• Change also the disk type and source file on User-PC.xml like this:

  <disk type='file' device='disk'>
  <driver name='qemu' type='qcow2'/>
     <source file='/images/User-PC.qcow2'/>
     <target dev='vda' bus='virtio'/>
     <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
  </disk>
  

• Add this xml file to the vm manager:

  virsh -c qemu:///system define User-PC.xml
  

• Start it:

  virsh start User-PC
  

Referencies:

• http://blog.mymediasystem.net/uncategorized/vmware-kvm-migration-guide/

Sometimes we need to access directly the disk of a virtual machine, without booting it. It can be done by mounting it on the host system, as in the following example.

modprobe nbd max_part=16
qemu-nbd -c /dev/nbd0 image.qcow2
partprobe /dev/nbd0
mount /dev/nbd0p1 /mnt/image

fdisk /dev/nbd0

vgscan
vgchange -ay zentyal

lvdisplay
mount /dev/zentyal/root /mnt/image
umount /mnt/image
vgchange -an zentyal
killall qemu-nbd

Reference: http://en.wikibooks.org/wiki/QEMU/Images