/usr/share/lxc/config/common.conf.d/00-lxcfs.conf is in lxcfs 2.0.0-0ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | lxc.hook.mount = /usr/share/lxcfs/lxc.mount.hook
lxc.hook.post-stop = /usr/share/lxcfs/lxc.reboot.hook
|