Lxd

LXD Skill

Manage LXD containers on Ubuntu hosts — launch, configure users, network, storage, and snapshots.

When to Use

• User asks to create, start, stop, or manage LXD containers
• Setting up default users with sudo access on LXD containers
• Configuring LXD networking (bridges, NAT, DHCP)
• Managing storage pools (ZFS, dir, btrfs)
• Taking/restoring snapshots
• Any LXD/LXC CLI interaction

Preferred Approach: Helper Scripts

For common multi-step operations, reach for scripts in scripts/ first:

# Usage:
./scripts/setup-user.sh <container> <username> [ssh_public_key_file_or_url]

# Examples:
./scripts/setup-user.sh pi bernard
./scripts/setup-user.sh webapp deploy ~/.ssh/id_ed25519.pub

Scripts keep variables in scope, handle cleanup, and reduce the chance of typos or forgotten steps.

Core Patterns

Launch a Container

lxc launch ubuntu:24.04 <name>

Set Up a User (Correct Way)

Do NOT use @filepath with -c user.user-data= — LXD passes the literal string as cloud-init data.

Instead, either:

1. Manual setup (simplest, most reliable):

   lxc exec <container> -- bash -c '
     useradd -m -s /bin/bash <username>
     usermod -aG sudo <username>
     echo "<username> ALL=(ALL) NOPASSWD:ALL" > /etc/sudoers.d/<username>
     chmod 440 /etc/sudoers.d/<username>
   '
   

2. Cloud-init via config-set (after launch):

   lxc launch ubuntu:24.04 <name>
   lxc config set <name> user.user-data "$(cat cloud-init.yaml)"
   lxc exec <name> -- cloud-init clean --reboot
   

3. Use the helper script — scripts/setup-user.sh

Verify Setup

lxc exec <container> -- id <username>
lxc exec <container> -- sudo -n whoami   # should return "root"

SSH Access

ssh <username>@<container-ip>

Get the IP with: lxc list

Container Lifecycle

lxc start <container>
lxc stop <container> [-f]              # force kill
lxc restart <container>
lxc delete <container> [-f]
lxc exec <container> -- bash
lxc shell <container>                  # interactive shell

Snapshots

lxc snapshot <container> <tag>
lxc restore <container> <snapshot-name>
lxc delete <container>/<snapshot-name>

Networking

lxc network list
lxc network show lxdbr0
lxc config set <container> network.eth0.ipv4.address <static-ip>  # static IP

Storage

lxc storage list
lxc storage create <pool-name> zfs source=/dev/sdX
lxc storage attach <pool-name> <disk-device> <container> <mount-point>

Gotchas

Decision Rules

• Simple user setup? → Manual lxc exec one-liner or scripts/setup-user.sh
• Complex provisioning (packages, config files)? → Cloud-init YAML via lxc config set
• Need reproducibility? → Snapshot before changes, or use lxc copy
• Multi-host management? → Use LXD remote: lxc remote add <name> <host>

Reference: Common Images