(It wasn't clear from your comment if you were aware of this) Since last year (docker 1.11) docker itself no longer is a runtime, and uses runC as the default runtime (https://blog.docker.com/2016/04/docker-engine-1-11-runc/)

Additional OCI compliant runtimes can be configured on the daemon (https://docs.docker.com/engine/reference/commandline/dockerd...), and can be selected per container, using the "--runtime" option on "docker run" (https://docs.docker.com/engine/reference/commandline/run/#op...)