Graphical setup of LXD (if needed on first run)

[marbetschar]

Right now Boxes expects LXD to be installed and initialized on the host system:

sudo apt install lxd
sudo lxd init            # use default values for everything

We should provide a graphical way to do so to improve the first run experience.

[toby63]

Just in case you didn't know, you can apply a configuration file to lxd init, via:
lxd init --preseed # Pre-seed mode, expects YAML config from stdin

Or use the auto flag for non-interactive configuration:
lxd init --auto
(you can also specify values for that, like [--storage-backend=dir])

from lxd init --help.