Slackware notes
===============
Docker daemon starts and runs as root.
To use the Docker command-line interface (the 'docker' program)
as a non-root user, you must add yourself to the 'docker' group:
  # gpasswd -a <your_username> docker
... and then restart the Docker daemon:
  # /etc/rc.d/rc.docker restart  
You will have to logoff and login again if you added yourself to the group.