Chapter 6. Tool support for image creation

Oz is a command-line tool that automates the process of creating a virtual machine image file. Oz is a Python app that interacts with KVM to step through the process of installing a virtual machine. It uses a predefined set of kickstart (RedHat-based systems) and preseed files (Debian-based systems) for operating systems that it supports, and it call also be using to create Microsoft Windows images. On Fedora, install Oz with yum:

# yum install oz

	Note
	As of this writing, there are no Oz packages for Ubuntu, so you will need to either install from source or build your own .deb file.

A full treatment of Oz is beyond the scope of this doucment, but we will provide an example. You can find additional examples of Oz template files on github at rackerjoe/oz-image-build/templates. Here's how you would create a CentOS 6.4 image with Oz.

Create a template file (we'll call it centos64.tdl) with the following contents. The only entry you will need to change is the <rootpw> contents.

<template>
  <name>centos64</name>
  <os>
    <name>CentOS-6</name>
    <version>4</version>
    <arch>x86_64</arch>
    <install type='iso'>
      <iso>http://mirror.rackspace.com/CentOS/6/isos/x86_64/CentOS-6.4-x86_64-bin-DVD1.iso</iso>
    </install>
    <rootpw>CHANGE THIS TO YOUR ROOT PASSWORD</rootpw>
  </os>
  <description>CentOS 6.4 x86_64</description>
  <repositories>
    <repository name='epel-6'>
      <url>http://download.fedoraproject.org/pub/epel/6/$basearch</url>
      <signed>no</signed>
    </repository>
  </repositories>
  <packages>
    <package name='epel-release'/>
    <package name='cloud-utils'/>
    <package name='cloud-init'/>
  </packages>
  <commands>
    <command name='update'>
yum -y update
yum clean all
sed -i '/^HWADDR/d' /etc/sysconfig/network-scripts/ifcfg-eth0
echo -n > /etc/udev/rules.d/70-persistent-net.rules
echo -n > /lib/udev/rules.d/75-persistent-net-generator.rules
    </command>
  </commands>
</template>

This Oz template specifies where to download the Centos 6.4 install ISO. Oz will use the version information to identify which kickstart file to use. In this case, it will be rhel-6-jeos.ks. It adds EPEL as a repository and install the epel-release, cloud-utils, and cloud-init packages, as specified in the packages section of the file.

After Oz does the initial OS install using the kickstart file, it will customize the image by doing an update and removing any reference to the eth0 device that libvirt creates while Oz was doing the customizing, as specified in the command section of the XML file.

To run this, do, as root:

# oz-install -d3 -u centos64.tdl -w centos64-libvirt.xml

If you leave out the -u flag, or you want to edit the file to do additional customizations, you can use the oz-customize command, using the libvirt XML file that oz-install creates. For example:

# oz-customize -d3 centos64.tdl centos64-libvirt.xml

Oz will invoke libvirt to boot the image inside of KVM, then Oz will ssh into the instance and perform the customizations.

vmbuilder (Virtual Machine Builder) is another command-line tool that can be used to create virtual machine images for different hypervisors. The version of vmbuilder that ships with Ubuntu can only create Ubuntu virtual machine guests. The version of vmbuilder that ships with Debian can create Ubuntu and Debian virtual machine guests.

The Ubuntu 12.04 server guide has documentation on how to use vmbuilder to create an Ubuntu image.

BoxGrinder  is another tool for creating virtual machine images, which it calls appliances. BoxGrinder can create Fedora, Red Hat Enterprise Linux, or CentOS images. BoxGrinder is currently only supported on Fedora.

VeeWee is often used to build Vagrant boxes, but it can also be used to build KVM images.

imagefactory is a newer tool designed to automate the building, converting, and uploading images to different cloud providers. It uses Oz as its back-end and includes support for OpenStack-based clouds.