Feb 4, 2014

KVM with Virt-Manager as a virtualization tool for Linux

I have use several operating system (OS) level virtualization tools like VMware Workstation, VMware Player, Oracle VirtualBox, Microsoft VirtualPC and KVM for many years.

Overall VMware Workstation is the best tool for me. But to use that we need to purchase a license.  As an alternative to VMware Workstation we can use VMware player (a stripdown version of WMware Workstation) for free but only for non-commercial use. Also you can't run multiple guest operating systems concurrently using that.

As an alternative to VMware products most of linux people use Oracle VirtualBox. I had some issues when I try to NAT a virtual instance (guest OS) on Ubuntu 12.10 (host OS) machine. As a solution for this most blogs forums suggest to change the virtual network option into Bridge. But most networks (including my home wifi network) doesn't allow this option because we do MAC address filtering.

Obviously you can not install Microsoft VirtualPC on a Linux host (even with vine). Truly I haven't use Xen, so I can't give any opinions on that.

kernel-based virtual machine (KVM) is another tool that we can use to do OS level virtualization. I will explain how to install KVM and Virt-Manager the graphical user interface which can use to interact with KVM on Ubuntu (Check this to install KVM on CentOS).

Installing KVM and Virt-manager on Ubuntu


Update your repository list
sudo apt-get update
Install packages and dependencies
sudo apt-get install kvm virt-manager
After completing the installation you can search for "Virtual machine Manager" on the search of Ubuntu Unity. Give the sudo password in the popup window.

Or else you can use the following command to start the virt-manager GUI from the terminal.
sudo virt-manager
In the first attempt it will prompt the following user interface. Use the default settings and click on "connect".

KVM Virt-Manager add connection

Installing guest operating system in KVM


Open virt-manager by clicking on the icon from unity search or using command. Then click on the left most icon of the GUI as follows. It will open a wizard to create a new virtual machine.

Create new virtual machine


Give a proper name, that name will appear on the virt-manager virtual machine list.

There are several ways to install an operating system and this tool also support few of them too. Usually we use a boot-able CD/DVD to install an operating system to a new machine/laptop. Also we can directly give the ISO image of an operating system.  Therefore, I will go ahead with the "Local installation media" option and click on "Forward"


In this I'm going to give an Ubuntu 12.04 desktop ISO image. Select the "Use ISO image" option and click on "Browse".


It will open another window which will list down all the image files of your virtual machines. Click on the bottom "Browse Local" button and browse to the ISO image that you need to install. Give the OS type and version in relevant fields. Then continue the wizard.


You can download those ISO images from relevant websites other than Windows.

In this step you need to set the guest machines memory and CPU. As I'm going to install a Ubuntu Desktop with the user interface (UI), I'm going to give 1024 MB of RAM and a single CPU will work for this.


Now we need to set the disk space. It is enough to give 8-10GB of disk space for a virtual (guest) machine.

Specially, remove the default check on the "Allocate entire disk now" option. If you do so, KVM will not allocate full 10GB (or what you set) from your host machines hard disk. It will only use the real data capacity used in the installation and only when you add data to the guest system it will grow. So this save lot of disk space.


In the last step you will get a confirmation page.

Few best practices when using KVM

  • To run virtual machine manager you need sudo permission. So you can create an alias for this.
alias virt-manager='sudo virt-manager'
sudo visudo
  • Add the line with your username
username ALL= NOPASSWD: ALL
  • Try to use text only installations of operating systems. It will reduce resources (RAM/disk space) usage. Most server edition operating systems by default install the text only (run level 3) environment.
  • Use base images
Create some base operating system installations in the system. If you need a virtual machine you can get a clone of the base installation and use. In this figure I have create three base images (virtual machines)
a CentOS, RHEL and a Ubuntu.

Other three machines are clones of a Ubuntu base machine which I used to simulate a Ubuntu base network. After the simulation I can delete those virtual machines with used virtual hard disk (.img file).


Install your favorite commonly used tools like vim/emacs, tree, htop, telnet, git, subversion, oracle JDK, links, debug tools and custom scripts.

Install additional repositories like EPEL, RPMForge,  repos on RedHat base distributions. Puppet repositories on all distributions.

So how to clone a virtual machine? Right click on the virtual machine (should be on power off state) and select "Clone" option. It will give the following window. Give a proper name for that and continue it. It will take few minutes to copy and the time will depend on your base image size.


When you need delete a virtual machine, select and right click on that and select "Delete" option. It will prompt another window as follows. Select the "Delete associated storage files" option and it will enable the list of storages which you need to delete in order to save your disk space. Keep in mind not to delete any iso images if those appear on this list.