Based on docker-systemd, this is Docker image with Ubuntu running systemd init system inside a container.
15.04 vivid
15.10 wily
docker run -it --cap-add SYS_ADMIN -v /sys/fs/cgroup:/sys/fs/cgroup:ro dockerimages/systemd:15.04 systemd.unit=emergency.service
You need CAP_SYS_ADMIN capability (as in the example above --caps-add SYS_ADMIN) or you can just add --privileged.