docker中pull镜像，报错 pull access denied for ubantu, repository does not exist or may require 'docker login'

Error Description: refusing to ubantu, warehouse does not exist or need to be logged docker

1. First, try to register docker  

2. Before pulling mirroring, log docker, command: docker login 

3. Then execute docker image pull ubantu still being given, the warehouse does not exist or need to be logged docker.

4. docker seacher ubantu, find the version

5. docker image pull oumuv/ubantu