Virtualization With KVM On Ubuntu 11.04

Version 1.0
Author: Falko Timme
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This guide explains how you can install and use KVM for creating and running virtual machines on an Ubuntu 11.04 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 and the IP address 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

sudo su 


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:

[email protected]:~# egrep '(vmx|svm)' --color=always /proc/cpuinfo
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext
 fxsr_opt rdtscp lm 3dnowext 3dnow rep_good nopl pni cx16 lahf_lm cmp_legacy svm extapic cr8_legacy 3dnowprefetch
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext
 fxsr_opt rdtscp lm 3dnowext 3dnow rep_good nopl pni cx16 lahf_lm cmp_legacy svm extapic cr8_legacy 3dnowprefetch
[email protected]:~#

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-pxe

General type of mail configuration: <-- Internet Site
System mail name: <--

Afterwards we must add the user as which we're currently logged in (root) to the group libvirtd:

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

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:

[email protected]:~# virsh -c qemu:///system list
 Id Name                 State

[email protected]:~#

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:

vi /etc/network/interfaces

Before the modification, my file looks as follows:

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static

I change it so that it looks like this:

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet manual

auto br0
iface br0 inet static
        bridge_ports eth0
        bridge_fd 9
        bridge_hello 2
        bridge_maxage 12
        bridge_stp off

(Make sure you use the correct settings for your network!)

Restart the network...

/etc/init.d/networking restart

... and run


It should now show the network bridge (br0):

[email protected]:~# ifconfig
br0       Link encap:Ethernet  HWaddr 00:1e:90:f3:f0:02
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::21e:90ff:fef3:f002/64 Scope:Link
          RX packets:16 errors:0 dropped:0 overruns:0 frame:0
          TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1516 (1.5 KB)  TX bytes:1440 (1.4 KB)

eth0      Link encap:Ethernet  HWaddr 00:1e:90:f3:f0:02
          inet6 addr: fe80::21e:90ff:fef3:f002/64 Scope:Link
          RX packets:36765 errors:0 dropped:0 overruns:0 frame:0
          TX packets:19112 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:54148967 (54.1 MB)  TX bytes:1523729 (1.5 MB)
          Interrupt:41 Base address:0xa000

lo        Link encap:Local Loopback
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

virbr0    Link encap:Ethernet  HWaddr 66:86:28:f1:a1:62
          inet addr:  Bcast:  Mask:
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

[email protected]:~#

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):

[email protected]:/var/lib/libvirt/images/vm1# vmbuilder kvm ubuntu -c vm2.cfg
2009-05-07 16:32:44,185 INFO     Cleaning up
ubuntu-kvm already exists
[email protected]:/var/lib/libvirt/images/vm1#

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
cp /etc/vmbuilder/libvirt/* /var/lib/libvirt/images/vm1/mytemplates/libvirt/

Now we come to the partitioning of our VM. We create a file called vmbuilder.partition...

vi /var/lib/libvirt/images/vm1/vmbuilder.partition

... and define the desired partitions as follows:

root 8000
swap 4000
/var 20000

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 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:

vi /var/lib/libvirt/images/vm1/
# This script will run the first time the virtual machine boots
# It is ran as root.

# Expire the user account
passwd -e administrator

# Install openssh-server
apt-get update
apt-get install -qqy --force-yes openssh-server

Make sure you replace the username administrator with your default login name.

(You can find more about this here:

(You can also define a "first login" script as described here:

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...

cd /var/lib/libvirt/images/vm1/

... and run vmbuilder, e.g. as follows:

vmbuilder kvm ubuntu --suite=natty --flavour=virtual --arch=amd64 --mirror= -o --libvirt=qemu:///system --ip= --gw= --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/ --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. If you leave out --mirror, then the default Ubuntu repository ( 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/

[email protected]:/var/lib/libvirt/images/vm1# ls -l /etc/libvirt/qemu/
total 8
drwxr-xr-x 3 root root 4096 2011-05-05 14:45 networks
-rw------- 1 root root 1795 2011-05-05 15:10 vm1.xml
[email protected]:/var/lib/libvirt/images/vm1#

The disk images are located in the ubuntu-kvm/ subdirectory of our VM directory:

ls -l /var/lib/libvirt/images/vm1/ubuntu-kvm/

[email protected]:/var/lib/libvirt/images/vm1# ls -l /var/lib/libvirt/images/vm1/ubuntu-kvm/
total 430040
-rw-r--r-- 1 root root 139264000 2011-05-05 15:10 tmp4hUoB1.qcow2
-rw-r--r-- 1 root root 301334528 2011-05-05 15:09 tmp5nFrU2.qcow2
[email protected]:/var/lib/libvirt/images/vm1#

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10 Comment(s)

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By: Anonymous


By: Anonymous

Instead of confusing the users with all this code, why can't you design a simple step-by-step "install wizard" with all the commands embedded?

All I would have to do is just download the "Install Wizard"!!!

I truly can't understand why do I have to bother will all that code...

Even though I am a Linux Fan, sorry, but Windows world is just so simpler...

I truly will not bother playing around with Virtualization in Linux if I have to bother with so much code, and so many articles.


By: Anonymous

You must have a very simple job. One that robots will be doing sometimes soon.

By: Anonymous

you have got to be kidding me! Windows is so much easier??? Really!! LMAO!

By: Tim

The beauty of Linux is that it is not cookie cutter like Windows.  Even though it is tougher to configure (code), it gives a you a better feeling of accomplishment when you do find success. This leads to more trials and victories, you gain proficiency along the way. 

By: David N

To avoid this problem:

Traceback (most recent call last):
  File "/usr/bin/vmbuilder", line 24, in <module>
  File "/usr/lib/python2.7/dist-packages/VMBuilder/contrib/", line 222, in main
  File "/usr/lib/python2.7/dist-packages/VMBuilder/contrib/", line 399, in set_disk_layout
IndexError: list index out of range

make sure that your vmbuilder.partition file has the columns separated by spaces, not tabs.  I learned the hard way!

By: David W

Thank You so much!  

Spent a whole day trying to figure this one out!! 

By: tim999

If you get an error indicating there are not enough Loops and you are running Ubuntu with Grub2, then you can increase Loops with the following.

First see how many loops you have with this command
ls /dev/loop*

Then edit grub module 10_linux
gedit /etc/grub.d/10_linux

Inside 10_linux, find the line that looks simular to the line below
linux ${rel_dirname}/${basename} root=${linux_root_device_thisversion} ro ${args}

Make the lline look like this -
linux ${rel_dirname}/${basename} root=${linux_root_device_thisversion} ro ${args} max_loop=64

Save it, 10_linux

Remember to run the command below (to incorporate the change)

ReBoot your system and rerun this command you should see 64 loops
ls /dev/loop*


Can't figure this text editor out:

No text is entered until I hit the o key.

Can't remove carriage returns.

Arrow keys behave erratically, sometimes entering A, C, etc characters when pressed.  This is on a normal 110 key keyboard.

Can't save.

Found Ctrl-C <Enter> :quit <Enter>, but that doesn't save.

No commands help available within the vi text editing screen.

It would be nice if this guide explicitly stated how to edit (and SAVE) files using the vi command from terminal.

 I know I've gotten lazy using Windows, but even in DOS I never had these kinds of troubles.  Makes me wish for a GUI based Virtual Machine installer, since this is all just so the kid can run some PC based games.  QEMU Launcher won't even get past Launch, no error, just nothing happens...  (Don't even ask about Play On Linux / Wine)

By: Anonymous

Have you never used vi before?  Google the commands for vi.  Quick reference:

 To edit (insert new characters or delete, etc.) hit "i" then start editing.

 To save and quite, press "esc" once done editing.  Then press ":" and type "wq".  That will write and quit.