Create cloud image VMs with UVtool

With Ubuntu being one of the most popular operating systems on many cloud platforms, the availability of stable and secure cloud images has become very important. Since Ubuntu 12.04, the use of cloud images outside of a cloud infrastructure has been improved so that it is now possible to use those images to create a virtual machine without needing a complete installation.

Creating virtual machines using uvtool

Starting with Ubuntu 14.04 LTS, a tool called uvtool has greatly facilitated the creation of virtual machines (VMs) using cloud images. uvtool provides a simple mechanism for synchronising cloud images locally and using them to create new VMs in minutes.

Install uvtool packages

The following packages and their dependencies are required in order to use uvtool:

  • uvtool

  • uvtool-libvirt

To install uvtool, run:

sudo apt -y install uvtool

This will install uvtool’s main commands, uvt-simplestreams-libvirt and uvt-kvm.

Get the Ubuntu cloud image with uvt-simplestreams-libvirt

This is one of the major simplifications that uvtool provides. It knows where to find the cloud images so you only need one command to get a new cloud image. For instance, if you want to synchronise all cloud images for the amd64 architecture, the uvtool command would be:

uvt-simplestreams-libvirt --verbose sync arch=amd64

After all the images have been downloaded from the Internet, you will have a complete set of locally-stored cloud images. To see what has been downloaded, use the following command:

uvt-simplestreams-libvirt query

Which will provide you with a list like this:

release=bionic arch=amd64 label=daily (20191107)
release=focal arch=amd64 label=daily (20191029)
...

In the case where you want to synchronise only one specific cloud image, you need to use the release= and arch= filters to identify which image needs to be synchronised.

uvt-simplestreams-libvirt sync release=DISTRO-SHORT-CODENAME arch=amd64

Furthermore, you can provide an alternative URL to fetch images from. A common case is the daily image, which helps you get the very latest images, or if you need access to the not-yet-released development release of Ubuntu. As an example:

uvt-simplestreams-libvirt sync --source http://cloud-images.ubuntu.com/daily [... further options]

Create a valid SSH key

To connect to the virtual machine once it has been created, you must first have a valid SSH key available for the Ubuntu user. If your environment does not have an SSH key, you can create one using the ssh-keygen command, which will produce similar output to this:

Generating public/private rsa key pair.
Enter file in which to save the key (/home/ubuntu/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/ubuntu/.ssh/id_rsa.
Your public key has been saved in /home/ubuntu/.ssh/id_rsa.pub.
The key fingerprint is:
4d:ba:5d:57:c9:49:ef:b5:ab:71:14:56:6e:2b:ad:9b ubuntu@DISTRO-SHORT-CODENAMES
The key's randomart image is:
+--[ RSA 2048]----+
|               ..|
|              o.=|
|          .    **|
|         +    o+=|
|        S . ...=.|
|         o . .+ .|
|        . .  o o |
|              *  |
|             E   |
+-----------------+

Create the VM using uvt-kvm

To create a new virtual machine using uvtool, run the following in a terminal:

uvt-kvm create firsttest

This will create a VM named ‘firsttest’ using the current locally-available LTS cloud image. If you want to specify a release to be used to create the VM, you need to use the release= filter, and the short codename of the release, e.g. “jammy”:

uvt-kvm create secondtest release=DISTRO-SHORT-CODENAME

The uvt-kvm wait command can be used to wait until the creation of the VM has completed:

uvt-kvm wait secondttest

Connect to the running VM

Once the virtual machine creation is completed, you can connect to it using SSH:

uvt-kvm ssh secondtest

You can also connect to your VM using a regular SSH session using the IP address of the VM. The address can be queried using the following command:

$ uvt-kvm ip secondtest
192.168.122.199
$ ssh -i ~/.ssh/id_rsa [email protected]
[...]
To run a command as administrator (user "root"), use "sudo <command>".
See "man sudo_root" for details.

ubuntu@secondtest:~$

Get the list of running VMs

You can get the list of VMs running on your system with the uvt-kvm list command.

Destroy your VM

Once you are finished with your VM, you can destroy it with:

uvt-kvm destroy secondtest

Note: Unlike libvirt’s destroy or undefine actions, this will (by default) also remove the associated virtual storage files.

More uvt-kvm options

The following options can be used to change some of the characteristics of the VM that you are creating:

  • --memory : Amount of RAM in megabytes. Default: 512.

  • --disk : Size of the OS disk in gigabytes. Default: 8.

  • --cpu : Number of CPU cores. Default: 1.

Some other parameters will have an impact on the cloud-init configuration:

  • --password <password> : Allows logging into the VM using the Ubuntu account and this provided password.

  • --run-script-once <script_file> : Run script_file as root on the VM the first time it is booted, but never again.

  • --packages <package_list> : Install the comma-separated packages specified in package_list on first boot.

A complete description of all available modifiers is available in the uvt-kvm manpages.

Resources

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