== How to teach CRIU to dump them ==
By default CRIU doesn't dump such mountpoints, because there's no way CRIU will be able to restore it -- the root of these mounts is out of
the scope of what CRIU dumped. In the logs you would see the message like
34:/bar doesn't have a proper root mount
will mean, that the mountpoint /bar has inaccessible root.
To dump and restore them there's the <code>--external mnt[KEY]:VAL</code> option that sets up external mounts root mapping.
On dump, KEY is a mountpoint inside container and
correspoding VAL is a string that will be written into the image as mountpoint's root value.
On restore KEY is the value from the image (VAL from dump) and the VAL is the path on host that will be bind-mounted into container (to the mountpoint path from image).
For example, if we want to dump the task above we should call