KVM Virtualisation on Ubuntu 22.04

I have been setting up a computer at home to act as a host for virtual machines. The machine is a recycled 10-year-old desktop with 4 cores, 32GB RAM and a 220GB SSD.

Growing the default disk

lvdisplay
lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv
lvdisplay
df -h
resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv
df -h

Installing kvm and libvirt

Installing packages:

apt install qemu-kvm libvirt-bin virtinst bridge-utils cpu-checker 
apt install libvirt-daemon-system virtinst libvirt-clients bridge-utils cloud-utils

Setting up users and starting daemons

systemctl enable --now libvirtd
systemctl start libvirtd
systemctl status libvirtd
usermod -aG libvirt simon

Setting up Networking

I needed to put the instance on a static IP and then create a bridge so any VMs that were launched were on the same network as everything else at home.

I followed these articles

First remove the default networks created by KVM

~# virsh net-destroy default
Network default destroyed

~# virsh net-undefine default
Network default has been undefined

then run “ip add show” to check just the physical network is left

backup and edit file in /etc/netplan ( 00-installer-config.yaml in my case) that has config for the network

Config created by installer:

# This is the network config written by 'subiquity'
network:
ethernets:
enp2s0:
dhcp4: true
version: 2

Replacement config:

network:
  ethernets:
    enp2s0:
      dhcp4: false
      dhcp6: false
  bridges:
    br0:
      interfaces: [enp2s0]
      addresses: [192.168.1.27/24]
      routes:
        - to: default
          via: 192.168.1.254
      mtu: 1500
      nameservers:
        addresses: [122.56.237.1, 210.55.111.1]
      parameters:
        stp: true
        forward-delay: 4
      dhcp4: false
      dhcp6: false
  version: 2

Note: The format in the 20.04 doc is slightly out of date (for the default route). Corrected in my file and the following link.

I used yamllint to check the config and “netplan try” and “netplan apply” to update.

Now we can make KVM aware of this bridge. create a scratch XML file called host-bridge.xml and insert the following:

<network>
  <name>host-bridge</name>
  <forward mode="bridge"/>
  <bridge name="br0"/>
</network>

Use the following commands to make that our default bridge for VMs:

virsh net-define host-bridge.xml
virsh net-start host-bridge
virsh net-autostart host-bridge

And then list the networks to confirm it is set to autostart:

$ virsh net-list --all
 Name          State    Autostart   Persistent
------------------------------------------------
 host-bridge   active   yes         yes

Booting a Virtual Machine

Now I want to create a Virtual machine image that I can base others I create off. I followed this guide:

Create Ubuntu 22.04 KVM Guest from a Cloud Image

First I downloaded the jammy-server-cloudimg-amd64.img from cloud-images.ubuntu.com. Note this is the ones that doesn’t have “disk” in it’s name.

~# wget http://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64.img

Then I grew the disk image to 10GB and copied it to where libvirt could see it.

~# qemu-img resize jammy-server-cloudimg-amd64.img +8G

~# cp ubuntu-18.04-server-cloudimg-arm64.img /var/lib/libvirt/images/jammy2204.img

Now I need to configure the image, especially with a user and password so I can login. The way to do this is with cloud-init. This is a special file of commands to config a booting virtual machine. The weird thing with KVM is that the file is on a virtual cdrom attached to the virtual machine.

First create the config

#cloud-config
system_info:
  default_user:
    name: simon
    home: /home/simon

password: hunter2
chpasswd: { expire: False }
hostname: ubuntu-22-cloud-image

# configure sshd to allow users logging in using password
# rather than just keys
ssh_pwauth: True

and save as bootconfig.txt . Then convert it to an iso and copy that to the images folder

~# cloud-localds bootconf.iso bootconf.txt
~# cp bootconf.iso /var/lib/libvirt/images/
~# virsh pool-refresh default

Now I run the program virt-manager locally. This is a graphical program that connects from my desktop over ssh to the the KVM server.

I use virt manager to connect to the KVM server and create a new virtual machine

  • Machine Type should be “Ubuutu 22.04 LTS”
  • It should boot off the jammy2204.img disk
  • The bootconf.iso should be attached to the CDROM. But the machine does not need to boot off it.
  • Set networking to be “Virtual network ‘host-bridge’: Bridge Network”

Boot the machine and you should be able to login to the console using the user:password you created in the cloud-config. You can then change passwords, update packages and otherwise configure the instance to you liking. Once you have finished you can shutdown the machine.

To create a new VM you just need to clone the disk:

~# virsh vol-clone --pool default jammy2204.img newvm.img

and then create a new Virtual machine in virt-manager using the disk (no need for the iso since the disk has the correct passwords)

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