[kentonv]

Once inside the container, you need to mount a tmpfs at /tmp, and another one at /run (which /var/run usually links to).

E.g.:

    mount -t tmpfs -o size=256M tmpfs /tmp

(I'm not sure if/how you can make Docker do this automatically. I'd imagine there's a flag or something.)

[doomrobo]

You could use the CMD keyword in the Dockerfile to ensure that that's run every time the container is started