Starting vncserver using supervisord inside a Linux container
You can define to run a container with specific user's name (if existing) or UID without any existing user in the image/container.
Docker documentation: https://docs.docker.com/engine/reference/run/#user
USER
root (id = 0) is the default user within a container. The image developer can create additional users. Those users are accessible by name. When passing a numeric ID, the user does not have to exist in the container.
The developer can set a default user to run the first process with the Dockerfile USER instruction. When starting a container, the operator can override the USER instruction by passing the -u option.
-u="": Username or UIDNote: if you pass a numeric uid, it must be in the range of 0-2147483647.