This is a short guide for setting up a Ubuntu VM template in Proxmox using CloudInit in a scriptable manor.

For this guide I have made a few assumptions:

• You want your VMs to boot via UEFI as opposed to BIOS
• Your Proxmox node's main storage is called local-zfs
• You want to use Ubuntu 22.04
• You have SSH keys stored in ~/.ssh/authorized_keys of your regular user's home folder

The first step is to download a cloud image for Ubuntu, then we'll resize this image

#wget -q https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64.img
#qemu-img resize jammy-server-cloudimg-amd64.img 32G

Notice that even though I'm resizing this image to be 32 gigabytes the file won't actually be 32 gigabytes in size, this is because the image is what's called a sparse file. The image starts out at around ~2GB but unless we resize the image now any cloned VMs won't have any storage. Feel free to change the 32G to 20, 80 or whatever you like.

The next step is to create a basic VM that we'll build upon:

#sudo qm create 8001 --name "ubuntu-2204-cloudinit-template" --ostype l26 \
    --memory 1024 \
    --agent 1 \
    --bios ovmf --machine q35 --efidisk0 local-zfs:0,pre-enrolled-keys=0 \
    --cpu host --socket 1 --cores 1 \
    --vga serial0 --serial0 socket  \
    --net0 virtio,bridge=vmbr0

Feel free to change the 8001 to whatever you like, so long as you replace the 8001 in subsequent commands to whatever you chose. The memory chosen doesn't really matter because this particular VM won't start, make sure to adjust the amount of RAM for cloned VMs. --agent enables the Qemu Guest Agent which is useful for all sorts of things like seeing the IP addresses of any interfaces. We'll set the CPU type to host (you almost always want this) with one socket and one core (remember to change the number of cores in cloned VMs). Next is the GPU, you can choose virtio instead of serial0 if you like but there's no need; serial gpu type does let you copy and paste which can be useful. Finally is the NIC, if you have a special bridge interface you want to choose change vmbr0 to whatever you like. If you want to use a VLAN tag add ,tag=## immediately after the bridge name (no spaces)

sudo qm importdisk 8001 jammy-server-cloudimg-amd64.img local-zfs
sudo qm set 8001 --scsihw virtio-scsi-pci --virtio0 local-zfs:vm-8001-disk-1,discard=on
sudo qm set 8001 --boot c --bootdisk virtio0
sudo qm set 8001 --ide2 local-zfs:cloudinit

The first command imports that image we downloaded earlier, if your disk storage is not local-zfs (for example local-lvm) then replace it with whatever you wish. Next command attaches the disk to the VM. If your disk storage is not on SSDs (which it should be) omit ,discard=on. The third command sets the boot order. Fourth adds the cloudinit pseudo-cdrom drive.

cat << EOF | sudo tee /var/lib/vz/snippets/vendor.yaml
#cloud-config
runcmd:
    - apt update
    - apt install -y qemu-guest-agent
    - systemctl start qemu-guest-agent
    - reboot
# Taken from https://forum.proxmox.com/threads/combining-custom-cloud-init-with-auto-generated.59008/page-3#post-428772
EOF

This file performs two purposes, the first rather obvious (installing qemu-guest-agent) the second not so much. For some reason CloudInit starts after networking and thus you can't SSH or even ping the VM by the name you give it. This package is only run once so after this reboot you'll be able to use the VM.

sudo qm set 8001 --cicustom "vendor=local:snippets/vendor.yaml"
sudo qm set 8001 --tags ubuntu-template,22.04,cloudinit
sudo qm set 8001 --ciuser untouchedwagons
sudo qm set 8001 --cipassword $(openssl passwd -6 $CLEARTEXT_PASSWORD)
sudo qm set 8001 --sshkeys ~/.ssh/authorized_keys
sudo qm set 8001 --ipconfig0 ip=dhcp

The first command tells CI to use the vendor file we specified earler. The second can be skipped but adds decorative tags that show up in the Proxmox Web-UI. Cloned VMs inherit all these tags. The third specifies the user to create. The fourth sets the password. The fifth imports SSH public keys so you can SSH in. Finally the virtio NIC is set to DHCP, this is supposed to be the default but manual specifying is necessary.

sudo qm template 8001

That's it! Your template is now ready to use. Clone this template as you wish (remember to adjust cores and RAM as needed) and start up the clone. After first boot Cloud-Init will kick in, create your user, install qemu-guest-agent and reboot. Once the reboot is complete you can SSH and use the VM however you like!

Thanks to ilude for telling me what command is needed to set the CI password.