Virtualization With KVM On Ubuntu 12.04 LTS
Submitted by falko (Contact Author) (Forums) on Sun, 2012-06-03 19:36. :: KVM | Ubuntu | Virtualization
Virtualization With KVM On Ubuntu 12.04 LTS
This guide explains how you can install and use KVM for creating and running virtual machines on an Ubuntu 12.04 LTS server. I will show how to create image-based virtual machines and also virtual machines that use a logical volume (LVM). KVM is short for Kernel-based Virtual Machine and makes use of hardware virtualization, i.e., you need a CPU that supports hardware virtualization, e.g. Intel VT or AMD-V.
I do not issue any guarantee that this will work for you!
1 Preliminary Note
I'm using a machine with the hostname server1.example.com and the IP address 192.168.0.100 here as my KVM host.
Because we will run all the steps from this tutorial with root privileges, we can either prepend all commands in this tutorial with the string sudo, or we become root right now by typing
2 Installing KVM And vmbuilder
First check if your CPU supports hardware virtualization - if this is the case, the command
egrep '(vmx|svm)' --color=always /proc/cpuinfo
should display something, e.g. like this:
root@server1:~# egrep '(vmx|svm)' --color=always /proc/cpuinfo
If nothing is displayed, then your processor doesn't support hardware virtualization, and you must stop here.
To install KVM and vmbuilder (a script to create Ubuntu-based virtual machines), we run
apt-get install ubuntu-virt-server python-vm-builder kvm-ipxe
Afterwards we must add the user as which we're currently logged in (root) to the group libvirtd:
adduser `id -un` libvirtd
You need to log out and log back in for the new group memberships to take effect.
To check if KVM has successfully been installed, run
virsh -c qemu:///system list
It should display something like this:
root@server1:~# virsh -c qemu:///system list
If it displays an error instead, then something went wrong.
Next we need to set up a network bridge on our server so that our virtual machines can be accessed from other hosts as if they were physical systems in the network.
To do this, we install the package bridge-utils...
apt-get install bridge-utils
... and configure a bridge. Open /etc/network/interfaces:
Before the modification, my file looks as follows:
I change it so that it looks like this:
(Make sure you use the correct settings for your network!)
Restart the network...
... and run
It should now show the network bridge (br0):
Before we start our first virtual machine, I recommend to reboot the system:
If you don't do this, you might get an error like open /dev/kvm: Permission denied in the virtual machine logs in the /var/log/libvirt/qemu/ directory.
3 Creating An Image-Based VM
We can now create our first VM - an image-based VM (if you expect lots of traffic and many read- and write operations for that VM, use an LVM-based VM instead as shown in chapter 6 - image-based VMs are heavy on hard disk IO).
I want to create my virtual machines in the directory /var/lib/libvirt/images/ (they cannot be created in the /root directory because the libvirt-qemu user doesn't have read permissions in that directory).
We will create a new directory for each VM that we want to create, e.g. /var/lib/libvirt/images/vm1, /var/lib/libvirt/images/vm2, /var/lib/libvirt/images/vm3, and so on, because each VM will have a subdirectory called ubuntu-kvm, and obviously there can be just one such directory in /var/lib/libvirt/images/vm1, for example. If you try to create a second VM in /var/lib/libvirt/images/vm1, for example, you will get an error message saying ubuntu-kvm already exists (unless you run vmbuilder with the --dest=DESTDIR argument):
root@server1:/var/lib/libvirt/images/vm1# vmbuilder kvm ubuntu -c vm2.cfg
We will use the vmbuilder tool to create VMs. (You can learn more about vmbuilder here.) vmbuilder uses a template to create virtual machines - this template is located in the /etc/vmbuilder/libvirt/ directory. First we create a copy:
mkdir -p /var/lib/libvirt/images/vm1/mytemplates/libvirt
Now we come to the partitioning of our VM. We create a file called vmbuilder.partition...
... and define the desired partitions as follows:
This defines a root partition (/) with a size of 8000MB, a swap partition of 4000MB, and a /var partition of 20000MB. The --- line makes that the following partition (/var in this example) is on a separate disk image (i.e., this would create two disk images, one for root and swap and one for /var). Of course, you are free to define whatever partitions you like (as long as you also define root and swap), and of course, they can be in just one disk image - this is just an example.
I want to install openssh-server in the VM. To make sure that each VM gets a unique OpenSSH key, we cannot install openssh-server when we create the VM. Therefore we create a script called boot.sh that will be executed when the VM is booted for the first time. It will install openssh-server (with a unique key) and also force the user (I will use the default username administrator for my VMs together with the default password howtoforge) to change the password when he logs in for the first time:
Make sure you replace the username administrator with your default login name.
(You can find more about this here: https://help.ubuntu.com/community/JeOSVMBuilder#First%20boot)
(You can also define a "first login" script as described here: https://help.ubuntu.com/community/JeOSVMBuilder#First%20login)
Now take a look at
vmbuilder kvm ubuntu --help
to learn about the available options.
To create our first VM, vm1, we go to the VM directory...
... and run vmbuilder, e.g. as follows:
vmbuilder kvm ubuntu --suite=precise --flavour=virtual --arch=amd64 --mirror=http://de.archive.ubuntu.com/ubuntu -o --libvirt=qemu:///system --ip=192.168.0.101 --gw=192.168.0.1 --part=vmbuilder.partition --templates=mytemplates --user=administrator --name=Administrator --pass=howtoforge --addpkg=vim-nox --addpkg=unattended-upgrades --addpkg=acpid --firstboot=/var/lib/libvirt/images/vm1/boot.sh --mem=256 --hostname=vm1 --bridge=br0
Most of the options are self-explanatory. --part specifies the file with the partitioning details, relative to our working directory (that's why we had to go to our VM directory before running vmbuilder), --templates specifies the directory that holds the template file (again relative to our working directory), and --firstboot specifies the firstboot script. --libvirt=qemu:///system tells KVM to add this VM to the list of available virtual machines. --addpkg allows you to specify Ubuntu packages that you want to have installed during the VM creation (see above why you shouldn't add openssh-server to that list and use the firstboot script instead). --bridge sets up a bridged network; as we have created the bridge br0 in chapter 2, we specify that bridge here.
In the --mirror line, you can specify an official Ubuntu repository in --mirror, e.g. http://de.archive.ubuntu.com/ubuntu. If you leave out --mirror, then the default Ubuntu repository (http://archive.ubuntu.com/ubuntu) will be used.
If you specify an IP address in the --ip switch, make sure that you also specify the correct gateway IP using the --gw switch (otherwise vmbuilder will assume that it is the first valid address in the network which might not be correct). Usually the gateway IP is the same that you use in /etc/network/interfaces (see chapter 2).
The build process can take a few minutes.
Afterwards, you can find an XML configuration file for the VM in /etc/libvirt/qemu/ (=> /etc/libvirt/qemu/vm1.xml):
ls -l /etc/libvirt/qemu/
root@server1:/var/lib/libvirt/images/vm1# ls -l /etc/libvirt/qemu/
The disk images are located in the ubuntu-kvm/ subdirectory of our VM directory:
ls -l /var/lib/libvirt/images/vm1/ubuntu-kvm/
root@server1:/var/lib/libvirt/images/vm1# ls -l /var/lib/libvirt/images/vm1/ubuntu-kvm/