print a helpful message if creating unpriv container with no idmap
This gives me:
ubuntu@c-t1:~$ lxc-create -t download -n u1
lxc_container: No mapping for container root
lxc_container: Error chowning /home/ubuntu/.local/share/lxc/u1/rootfs to container root
lxc_container: You must either run as root, or define uid mappings
lxc_container: To pass uid mappings to lxc-create, you could create
lxc_container: ~/.config/lxc/default.conf:
lxc_container: lxc.include = /etc/lxc/default.conf
lxc_container: lxc.id_map = u 0 100000 65536
lxc_container: lxc.id_map = g 0 100000 65536
lxc_container: Error creating backing store type (none) for u1
lxc_container: Error creating container u1
when I create a container without having an id mapping defined.