Comment 2 for bug 1393932

The issue is that there was a template container plus config generated by Juju 1.20 or earlier. This template container is used (when lxc-clone is true) to make container creattion fast. But the template config is out of date with 1.21, because it contains a bind mount to a tools directory that no longer exists in 1.21.

So, an upgrade to 1.21 should check for existing lxc templates and do something - whether that's warning the user and advising them to delete the template, or attempting to parse and fix the lxc config, I'm not sure.