docker login command allows you to login to docker.com. You need to login to docker before you can upload your own images to docker hub. This is also needed if you need to pull down a private image.
root@ok:~# docker login Login with your Docker ID to push and pull images from Docker Hub. If you don't have a Docker ID, head over to https://hub.docker.com to create one. Username: serverok Password: Login Succeeded root@ok:~#
if you need to login to a different docker registery, for example your company docker registery, use
docker login IP_OR_HOST_OF_DOCKER_REGISTRY:PORT
To log off, use
docker logout
or
docker logout IP_OR_HOST_OF_DOCKER_REGISTRY:PORT