Where are the LXC container configuration files located?
Solution 1:
I guess you are talking about the 'old' LXC containers. In case you are running Ubuntu 16.04 or Ubuntu 16.10, everything is located in the /var/lib/lxd folder, also the commands changed.
To get a list of the available commands, execute lxc help --all and for deeper information lxc manpage. Here you can find additional useful information about the "newer" LXD system containers in Ubuntu :
Linux Containers - LXD
LXD doc / configuration
The LXD 2.0 Story series