Prepare the host and LXD

Phases 01 and 02: update the Ubuntu host, check it can run virtual machines, install LXD from the long-term-support track, and open the LXD web UI in your browser.

Phase 01 · Prepare the Ubuntu host (~15 min)

Confirm hardware virtualisation works.
Install LXD 5.21 LTS and hold it at that version.
Initialise LXD with a ZFS storage pool.

Host: update the system and check virtualisation

sudo apt update && sudo apt full-upgrade -y
sudo apt install -y cpu-checker nftables
kvm-ok
# Expected: "KVM acceleration can be used"

Host: install LXD 5.21 LTS and hold it

Install from the 5.21 LTS track (supported until June 2029), hold it so it cannot jump to a new version without you, and add yourself to the lxd group.

snap list lxd 2>/dev/null || sudo snap install lxd --channel=5.21/stable
sudo snap refresh lxd --channel=5.21/stable     # no-op if already on 5.21/stable
sudo snap refresh --hold lxd                    # stop automatic updates (undo: --unhold)
sudo usermod -aG lxd "$USER"
newgrp lxd          # or log out and back in
lxc version                                      # Client/Server version: 5.21.x LTS

Host: run the first-time setup

lxd init

Answer the questions like this:

Question	Answer	Why
Would you like to use LXD clustering?	no	One machine
Do you want to configure a new storage pool?	yes
Name of the new storage pool	default
Name of the storage backend	zfs	Instant snapshots, thin disks
Create a new ZFS pool?	yes
Use an existing empty block device?	no	Uses a file on your disk; simplest
Size in GiB of the new loop device	200	Sparse file: grows only as used. The lab used about 2 GiB; 100 is plenty if space is tight.
Connect to a MAAS server?	no
Create a new local network bridge?	no	You create the lab network yourself next
Configure LXD to use an existing bridge or host interface?	no
Would you like the LXD server to be available over the network?	yes	Needed for the web UI
Address to bind LXD to	`<HOST_LAN_IP>`	Only the host's LAN address, never the lab network
Port to bind LXD to	8443
Would you like stale cached images to be updated automatically?	yes
Print a YAML "lxd init" preseed?	no

Phase 02 · Open the LXD UI (~5 min)

LXD UI: open the address

From any browser on your local network, go to https://<HOST_LAN_IP>:8443. Accept the self-signed certificate warning (Advanced → Proceed).

LXD UI: create a certificate

Choose Create a new certificate and follow the wizard: Generate → copy the command it shows → run it on the host → Download .pfx → import it into your browser → restart the browser.

lxc config trust add --name lxd-ui
# newer LXD 6.x shows: lxc auth identity create tls/lxd-ui --group admins

LXD UI: log in

Reload the page and pick the certificate when asked. You should land on Instances.