Build on LXD

Snapcraft 3, the snap-building tool, is designed to use a combination of Multipass and bases to both simplify the build process and to confine the build environment within a virtual machine. This mostly removes the need to use LXD.

However, it’s still possible to use LXD if you’d prefer.

• If you are using bases and Snapcraft version 3.4+ you can request to use LXD with the --use-lxd argument:

  $ snapcraft --use-lxd
  

• If your snapcraft.yaml doesn’t use bases, you should continue using snapcraft cleanbuild.

See below for help on installing LXD, manually building snaps within an LXD environment and building without bases.

Install LXD

Recent non-desktop versions of Ubuntu install LXD by default - you can check whether it is installed with the following command:

$ lxd version
3.13

The easiest way to add LXD to your system is via its snap:

$ sudo snap install lxd

Now initialise LXD with the following command, accepting all the default options unless you have specific requirements:

$ sudo lxd init

Error: Failed to create network 'lxdbr0': Failed to automatically find an unused IPv4 subnet, manual configuration required

$ sudo lxc network create lxdbr0 ipv4.address=10.0.3.1/24 ipv4.nat=true

Would you like to create a new network bridge (yes/no) [default=yes]? no

Group permissions

If you want to build snaps as a non-root user, which is advised, then you need to add your user account to the lxd group:

$ sudo usermod -a -G lxd ${USER}

You now need to either restart your session, reboot your computer, or use newgrp to acquire the new group assignment:

$ newgrp lxd

Building with bases

Snapcraft with LXD operates in much the same way as snapcraft with a default Multipass environment. However, with LXD installed and configured, you need to manually add the --use-lxd argument to initiate the build within LXD:

$ snapcraft --use-lxd

Many of the snapcraft’s Multipass operations also work with LXD, including:

• --shell
• --shell-after
• --debug

Similarly, snapcraft’s lifecycle commands, pull, build, stage and prime, together with clean, can also use the --use-lxd option.

$ snapcraft clean --use-lxd
The LXD provider is offered as a technology preview for early adopters.
The command line interface, container names or lifecycle handling may change in upcoming releases.

Building without bases

To build your project using lxd run:

$ cd $HOME/my-snap-project
$ snapcraft cleanbuild

If the build fails, add the --debug option to the snapcraft command. This will drop you into a shell running within the LXD environment that just attempted to build your snap, allowing you to examine where the issue may be.

Building manually

These instructions are intended to be only a general guide. For further details on using LXD as a container environment, see the LXD Documentation.

First, create and run a new container based on Ubuntu 18.04 LTS (Bionic Beaver). Our example calls this container mysnapcraft:

$ lxc launch ubuntu:18.04 mysnapcraft

Copy your snap’s snapcraft.yaml to this new container:

$ lxc file push snap/snapcraft.yaml mysnapcraft/home/ubuntu/

Now open an interactive shell within your container and install snapcraft:

$ lxc exec mysnapcraft -- /bin/bash 
$ snap install snapcraft --classic

Finally, staying within the container, start the build by running snapcraft with the --destructive-mode argument. This forces snapcraft to build the snap directly within the current host (the mysnapcraft LXD container):

$ cd /home/ubuntu
$ snapcraft --destructive-mode

You can troubleshoot the build process just as you would on the native machine. The container is persistent and will remain until stopped and deleted.

With the build complete, you can copy your new snap to your native environment with the following command:

$ lxc file pull mysnapcraft/home/ubuntu/mysnap.snap .