When I run a basic Docker container (from within Google Cloud Shell) like so
docker pull debian
docker run -i -t debian:wheezy /bin/bash
and then type runlevel at the running container's shell prompt, the run level is unknown. Am I supposed to install (apt-get) particular packages in order to add support for run levels. If so, which ones, or what else could be wrong?
Docker is an application isolation tool, not an OS virtualization tool. Runlevels are at the OS level, the OS comes up, mounts directories, and starts services to achieve a runlevel. In a container, your application is launched, the end. You can assume the container is at a single user run level, since you're the only user accessing the environment, but it really shouldn't matter for installing applications.