$ sudo docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
af8da3cff175        registry:2          "/entrypoint.sh /etc…"   17 minutes ago      Up 3 minutes        5000/tcp            registry

$ sudo docker exec -it registry /bin/sh
/ # ps
PID   USER     TIME  COMMAND
    1 root      0:00 registry serve /etc/docker/registry/config.yml
   14 root      0:00 /bin/sh
   20 root      0:00 ps
/ # netstat -ln
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 127.0.0.1:5000          0.0.0.0:*               LISTEN