By default, if I issue command:
sudo docker pull ruby:2.2.1
it will pull from the docker.io offical site by default.
Pulling repository docker.io/library/ruby
How do I change it to my private registry. That means if I issue
sudo docker pull ruby:2.2.1
it will pull from my own private registry, the output is something like:
Pulling repository my_private.registry:port/library/ruby
UPDATE: Following your comment, it is not currently possible to change the default registry, see this issue for more info.
You should be able to do this, substituting the host and port to your own:
docker pull localhost:5000/registry-demo
If the server is remote/has auth you may need to log into the server with:
docker login https://<YOUR-DOMAIN>:8080
Then running:
docker pull <YOUR-DOMAIN>:8080/test-image