Despite there being closed bugs about this in docker's bug tracker
(https://github.com/docker/docker/issues/5663)
it remains a problem to use ssh and cron in docker containers, because
pam_loginuid.so fails to work inside docker in the default
configuration.

Workaround is to make the /etc/pam.d/ lines for pam_loginuid.so
s/required/optional/.

I think this workaround is being applied to some of the standard docker
containers (perhaps inconsistently based on other reports like
https://github.com/docker/docker/pull/7873).
Which leaves it as a land-mine for anyone who builds their own custom
containers using Debian.

I don't think that Debian should need to be tweaked to be used in a
docker container, so I hope this can be really fixed somehow.