I was naively expecting this command to run a bash shell in a running container :
docker run \"id of running container\" /bin/bash
it look
Keep an eye on this pull request: https://github.com/docker/docker/pull/7409
Which implements the forthcoming docker exec utility. When this is available it should be possible to e.g. start and stop the ssh service inside a running container.
There is also nsinit to do this: "nsinit provides a handy way to access a shell inside a running container's namespace", but it looks difficult to get running.
https://gist.github.com/ubergarm/ed42ebbea293350c30a6