/usr/lib/x86_64-linux-gnu/lxc/README is in liblxc1 3.0.1-0ubuntu1~18.04.2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | This directory must exist, even though it may be empty.
It is used to temporary mount the rootfs of lxc in a private
mount namespace only visible by the processes running in the
container.
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