/usr/share/lxc/config/plamo.userns.conf is in lxc-templates 3.0.0-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | # This derives from the global userns config
lxc.include = /usr/share/lxc/config/userns.conf
|