JeOS and vmbuilder


What is JeOS

Ubuntu JeOS (pronounced "Juice") is an efficient variant of the Ubuntu Server operating system, configured specifically for virtual appliances. No longer available as a CD-ROM ISO for download, but only as an option either:

  • While installing from the Server Edition ISO (pressing F4 on the first screen will allow you to pick "Minimal installation", which is the package selection equivalent to JeOS).

  • Or to be built using Ubuntu's vmbuilder, which is described here.

JeOS is a specialized installation of Ubuntu Server Edition with a tuned kernel that only contains the base elements needed to run within a virtualized environment.

Ubuntu JeOS has been tuned to take advantage of key performance technologies in the latest virtualization products from VMware. This combination of reduced size and optimized performance ensures that Ubuntu JeOS Edition delivers a highly efficient use of server resources in large virtual deployments.

Without unnecessary drivers, and only the minimal required packages, ISVs can configure their supporting OS exactly as they require. They have the peace of mind that updates, whether for security or enhancement reasons, will be limited to the bare minimum of what is required in their specific environment. In turn, users deploying virtual appliances built on top of JeOS will have to go through fewer updates and therefore less maintenance than they would have had to with a standard full installation of a server.

What is vmbuilder

With vmbuilder, there is no need to download a JeOS ISO anymore. vmbuilder will fetch the various package and build a virtual machine tailored for our need in about a minute for us. Vmbuilder is a Script that automates the process of creating a ready to use Linux based VM. The currently supported hypervisors are KVM and Xen.

You can pass command line options to add extra packages, remove packages, choose which version of Ubuntu, which mirror etc. On recent hardware with plenty of RAM, tmpdir in /dev/shm or using a tmpfs, and a local mirror, you can bootstrap a VM in less than a minute.

First introduced as a shell script in Ubuntu 8.04LTS, ubuntu-vm-builder started with little emphasis as a hack to help developers test their new code in a virtual machine without having to restart from scratch each time. As a few Ubuntu administrators started to notice this script, a few of them went on improving it and adapting it for so many use case that Soren Hansen (the author of the script and Ubuntu virtualization specialist, not the golf player) decided to rewrite it from scratch for Intrepid as a python script with a few new design goals:

  • Develop it so that it can be reused by other distributions.

  • Use a plugin mechanisms for all virtualization interactions so that others can easily add logic for other virtualization environments.

  • Provide an easy to maintain web interface as an option to the command line interface.

But the general principles and commands remain the same.

Initial Setup

It is assumed that you have installed and configured libvirt and KVM locally on the machine you are using. For details on how to perform this, please refer to:

We also assume that you know how to use a text based text editor such as nano or vi. If you have not used any of them before, you can get an overview of the various text editors available by reading the PowerUsersTextEditors page. This tutorial has been done on KVM, but the general principle should remain on other virtualization technologies.

Install vmbuilder

The name of the package that we need to install is python-vm-builder. In a terminal prompt enter:

sudo apt-get install python-vm-builder

If you are running Hardy, you can still perform most of this using the older version of the package named ubuntu-vm-builder, there are only a few changes to the syntax of the tool.

Defining Your Virtual Machine

Defining a virtual machine with Ubuntu's vmbuilder is quite simple, but here are a few thing to consider:

  • If you plan on shipping a virtual appliance, do not assume that the end-user will know how to extend disk size to fit their need, so either plan for a large virtual disk to allow for your appliance to grow, or explain fairly well in your documentation how to allocate more space. It might actually be a good idea to store data on some separate external storage.

  • Given that RAM is much easier to allocate in a VM, RAM size should be set to whatever you think is a safe minimum for your appliance.

The vmbuilder command has 2 main parameters: the virtualization technology (hypervisor) and the targeted distribution. Optional parameters are quite numerous and can be found using the following command:

vmbuilder --help

Base Parameters

As this example is based on KVM and Ubuntu 9.10 (Karmic Koala), and we are likely to rebuild the same virtual machine multiple time, we'll invoke vmbuilder with the following first parameters:

sudo vmbuilder kvm ubuntu --suite karmic --flavour virtual --arch i386 -o --libvirt qemu:///system

The --suite defines the Ubuntu release, the --flavour specifies that we want to use the virtual kernel (that's the one used to build a JeOS image), the --arch tells that we want to use a 32 bit machine, the -o tells vmbuilder to overwrite the previous version of the VM and the --libvirt tells to inform the local virtualization environment to add the resulting VM to the list of available machines.


  • Because of the nature of operations performed by vmbuilder, it needs to have root privilege, hence the use of sudo.

  • If your virtual machine needs to use more than 3Gb of ram, you should build a 64 bit machine (--arch amd64).

  • Until Ubuntu 8.10, the virtual kernel was only built for 32 bit architecture, so if you want to define an amd64 machine on Hardy, you should use --flavour server instead.

JeOS Installation Parameters

Xarxes del JeOS
Assigning a fixed IP address

As a virtual appliance that may be deployed on various very different networks, it is very difficult to know what the actual network will look like. In order to simplify configuration, it is a good idea to take an approach similar to what network hardware vendors usually do, namely assigning an initial fixed IP address to the appliance in a private class network that you will provide in your documentation. An address in the range is usually a good choice.

To do this we'll use the following parameters:

  • --ip ADDRESS: IP address in dotted form (defaults to dhcp if not specified)

  • --mask VALUE: IP mask in dotted form (default:

  • --net VALUE: IP net address (default: X.X.X.0)

  • --bcast VALUE: IP broadcast (default: X.X.X.255)

  • --gw ADDRESS: Gateway address (default: X.X.X.1)

  • --dns ADDRESS: Name server address (default: X.X.X.1)

We assume for now that default values are good enough, so the resulting invocation becomes:

sudo vmbuilder kvm ubuntu --suite karmic --flavour virtual --arch i386 -o --libvirt qemu:///system --ip
Modifying the libvirt Template to use Bridging

Because our appliance will be likely to need to be accessed by remote hosts, we need to configure libvirt so that the appliance uses bridge networking. To do this we use vmbuilder template mechanism to modify the default one.

In our working directory we create the template hierarchy and copy the default template:

mkdir -p VMBuilder/plugins/libvirt/templates
cp /etc/vmbuilder/libvirt/* VMBuilder/plugins/libvirt/templates/

We can then edit VMBuilder/plugins/libvirt/templates/libvirtxml.tmpl to change:

          <interface type='network'>
            <source network='default'/>


          <interface type='bridge'>
            <source bridge='br0'/>

Partitioning of the virtual appliance will have to take into consideration what you are planning to do with is. Because most appliances want to have a separate storage for data, having a separate /var would make sense.

In order to do this vmbuilder provides us with --part:

--part PATH
  Allows to specify a partition table in partfile each  line  of  partfile  should  specify
  (root first):
      mountpoint size
  where  size  is  in megabytes. You can have up to 4 virtual disks, a new disk starts on a
  line with ’---’.  ie :
      root 1000
      /opt 1000
      swap 256
      /var 2000
      /log 1500

In our case we will define a text file name vmbuilder.partition which will contain the following:

root 8000
swap 4000
/var 20000

Note that as we are using virtual disk images, the actual sizes that we put here are maximum sizes for these volumes.

Our command line now looks like:

sudo vmbuilder kvm ubuntu --suite karmic --flavour virtual --arch i386 \ -o --libvirt qemu:///system --ip --part vmbuilder.partition

Using a "\" in a command will allow long command strings to wrap to the next line.

User and Password

Again setting up a virtual appliance, you will need to provide a default user and password that is generic so that you can include it in your documentation. We will see later on in this tutorial how we will provide some security by defining a script that will be run the first time a user actually logs in the appliance, that will, among other things, ask him to change his password. In this example I will use 'user' as my user name, and 'default' as the password.

To do this we use the following optional parameters:

  • --user USERNAME: Sets the name of the user to be added. Default: ubuntu.

  • --name FULLNAME: Sets the full name of the user to be added. Default: Ubuntu.

  • --pass PASSWORD: Sets the password for the user. Default: ubuntu.

Our resulting command line becomes:

sudo vmbuilder kvm ubuntu --suite intrepid --flavour virtual --arch i386 \ -o --libvirt qemu:///system --ip --part vmbuilder.partition \ --user user --name user --pass default

Installing Required Packages

In this example we will be installing a package (Limesurvey) that accesses a MySQL database and has a web interface. We will therefore require our OS to provide us with:

  • Apache

  • PHP

  • MySQL

  • Servidor OpenSSH

  • Limesurvey (as an example application that we have packaged)

This is done using vmbuilder by specifying the --addpkg command multiple times:

--addpkg PQT
  Instal·la el PQT a l'amfitrió (es pot especificar diverses vegades)

However, due to the way vmbuilder operates, packages that have to ask questions to the user during the post install phase are not supported and should instead be installed while interactivity can occur. This is the case of Limesurvey, which we will have to install later, once the user logs in.

Other packages that ask simple debconf question, such as mysql-server asking to set a password, the package can be installed immediately, but we will have to reconfigure it the first time the user logs in.

If some packages that we need to install are not in main, we need to enable the additional repositories using --comp and --ppa:

--components COMP1,COMP2,...,COMPN
           A comma separated list of distro components to include (e.g. main,universe). This defaults
           to "main"
--ppa=PPA  Add ppa belonging to PPA to the vm's sources.list.

Limesurvey not being part of the archive at the moment, we'll specify it's PPA (personal package archive) address so that it is added to the VM /etc/apt/source.list, so we add the following options to the command line:

--addpkg apache2 --addpkg apache2-mpm-prefork --addpkg apache2-utils --addpkg apache2.2-common \ --addpkg dbconfig-common --addpkg libapache2-mod-php5 --addpkg mysql-client --addpkg php5-cli \ --addpkg php5-gd --addpkg php5-ldap --addpkg php5-mysql --addpkg wwwconfig-common \ --addpkg mysql-server --ppa nijaba

Another convenient tool that we want to have on our appliance is OpenSSH, as it will allow our admins to access the appliance remotely. However, pushing in the wild an appliance with a pre-installed OpenSSH server is a big security risk as all these server will share the same secret key, making it very easy for hackers to target our appliance with all the tools they need to crack it open in a breeze. As for the user password, we will instead rely on a script that will install OpenSSH the first time a user logs in so that the key generated will be different for each appliance. For this we'll use a --firstboot script, as it does not need any user interaction.

Speed Considerations

Package Caching

When vmbuilder creates builds your system, it has to go fetch each one of the packages that composes it over the network to one of the official repositories, which, depending on your internet connection speed and the load of the mirror, can have a big impact on the actual build time. In order to reduce this, it is recommended to either have a local repository (which can be created using apt-mirror) or using a caching proxy such as apt-cache. The later option being much simpler to implement and requiring less disk space, it is the one we will pick in this tutorial. To install it, simply type:

sudo apt-get install apt-proxy

Once this is complete, your (empty) proxy is ready for use on http://mirroraddress:9999 and will find ubuntu repository under /ubuntu. For vmbuilder to use it, we'll have to use the --mirror option:

--mirror=URL  Use Ubuntu mirror at URL instead of the default, which
              is for official
              arches and

So we add to the command line:

--mirror http://mirroraddress:9999/ubuntu

The mirror address specified here will also be used in the /etc/apt/source.list of the newly created guest, so it is usefull to specify here an address that can be resolved by the guest or to plan on reseting this address later on, such as in a --firstboot script.

Install a Local Mirror

If we are in a larger environment, it may make sense to setup a local mirror of the Ubuntu repositories. The package apt-mirror provides you with a script that will handle the mirroring for you. You should plan on having about 20 gigabyte of free space per supported release and architecture.

By default, apt-mirror uses the configuration file in /etc/apt/mirror.list. As it is set up, it will replicate only the architecture of the local machine. If you would like to support other architectures on your mirror, simply duplicate the lines starting with “deb”, replacing the deb keyword by /deb-{arch} where arch can be i386, amd64, etc... For example, on an amd64 machine, to have the i386 archives as well, you will have:

deb karmic main restricted universe multiverse 
/deb-i386 karmic main restricted universe multiverse

deb karmic-updates main restricted universe multiverse 
/deb-i386 karmic-updates main restricted universe multiverse 

deb karmic-backports main restricted universe multiverse 
/deb-i386 karmic-backports main restricted universe multiverse 

deb karmic-security main restricted universe multiverse 
/deb-i386 karmic-security main restricted universe multiverse 

deb karmic main/debian-installer restricted/debian-installer universe/debian-installer multiverse/debian-installer 
/deb-i386 karmic main/debian-installer restricted/debian-installer universe/debian-installer multiverse/debian-installer 

Notice that the source packages are not mirrored as they are seldom used compared to the binaries and they do take a lot more space, but they can be easily added to the list.

Once the mirror has finished replicating (and this can be quite long), you need to configure Apache so that your mirror files (in /var/spool/apt-mirror if you did not change the default), are published by your Apache server. For more information on Apache see “HTTPD - Apache2 Web Server”.

Installing in a RAM Disk

As you can easily imagine, writing to RAM is a LOT faster than writing to disk. If you have some free memory, letting vmbuilder perform its operation in a RAMdisk will help a lot and the option --tmpfs will help you do just that:

--tmpfs OPTS  Use a tmpfs as the working directory, specifying its
              size or "-" to use tmpfs default (suid,dev,size=1G).

So adding --tmpfs - sounds like a very good idea if you have 1G of free ram.

Package the Application

Two option are available to us:

  • The recommended method to do so is to make a Debian package. Since this is outside of the scope of this tutorial, we will not perform this here and invite the reader to read the documentation on how to do this in the Ubuntu Packaging Guide. In this case it is also a good idea to setup a repository for your package so that updates can be conveniently pulled from it. See the Debian Administration article for a tutorial on this.

  • Manually install the application under /opt as recommended by the FHS guidelines.

In our case we'll use Limesurvey as example web application for which we wish to provide a virtual appliance. As noted before, we've made a version of the package available in a PPA (Personal Package Archive).

Finishing Install

First Boot

As we mentioned earlier, the first time the machine boots we'll need to install openssh-server so that the key generated for it is unique for each machine. To do this, we'll write a script called as follows:

# This script will run the first time the virtual machine boots
# It is ran as root.

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

And we add the --firstboot option to our command line.

First Login

Mysql and Limesurvey needing some user interaction during their setup, we'll set them up the first time a user logs in using a script named We'll also use this script to let the user specify:

  • His own password

  • Define the keyboard and other locale info he wants to use

So we'll define as follows:

# This script is ran the first time a user logs in

echo "Your appliance is about to be finished to be set up."
echo "In order to do it, we'll need to ask you a few questions,"
echo "starting by changing your user password."


#give the opportunity to change the keyboard
sudo dpkg-reconfigure console-setup

#configure the mysql server root password
sudo dpkg-reconfigure mysql-server-5.0

#install limesurvey
sudo apt-get install -qqy --force-yes limesurvey

echo "Your appliance is now configured.  To use it point your"
echo "browser to http://serverip/limesurvey/admin"

And we add the --firstlogin option to our command line.

Useful Additions

Configuració de les actualitzacions automàtiques

To have your system be configured to update itself on a regular basis, we will just install unattended-upgrades, so we add the following option to our command line:

--addpkg unattended-upgrades

As we have put our application package in a PPA, the process will update not only the system, but also the application each time we update the version in the PPA.

ACPI Event Handling

For your virtual machine to be able to handle restart and shutdown events it is being sent, it is a good idea to install the acpid package as well. To do this we just add the following option:

--addpkg acpid

Final Command

Here is the command with all the options discussed above:

sudo vmbuilder kvm ubuntu --suite intrepid --flavour virtual --arch i386 -o \ 
         --libvirt qemu:///system --ip --part vmbuilder.partition --user user \
         --name user --pass default --addpkg apache2 --addpkg apache2-mpm-prefork \ 
         --addpkg apache2-utils --addpkg apache2.2-common --addpkg dbconfig-common \ 
         --addpkg libapache2-mod-php5 --addpkg mysql-client --addpkg php5-cli \ 
         --addpkg php5-gd --addpkg php5-ldap --addpkg php5-mysql --addpkg wwwconfig-common \
         --addpkg mysql-server --addpkg unattended-upgrades --addpkg acpid --ppa nijaba \ 
         --mirror http://mirroraddress:9999/ubuntu --tmpfs - --firstboot \
         --firstlogin es


If you are interested in learning more, have questions or suggestions, please contact the Ubuntu Server Team at: