As Jérôme Petazzoni mentioned in docker-user group:
Actually, you can SIGKILL the client, and reattach later. However, this will disrupt stdin (the container will see EOF on stdin, and if it cares about stdin, e.g. if it's a shell, it will exit). To recap: docker run -t -i → can be detached with ^P^Q and reattached with docker attach docker run -i → cannot be detached with ^P^Q; will disrupt stdin docker run → cannot be detached with ^P^Q; can SIGKILL client; can reattach with docker attach