/etc/update-motd.d/97-overlayroot is in overlayroot 0.40ubuntu1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 | #!/bin/sh
(egrep "overlayroot|/media/root-ro|/media/root-rw" /proc/mounts 2>/dev/null | sort -r) || true
echo
|