[root]# docker login --help
Usage:  docker login [OPTIONS] [SERVER]

Log in to a Docker registry.
If no server is specified, the default is defined by the daemon.

Options:
  -p, --password string   Password
      --password-stdin    Take the password from stdin
  -u, --username string   Username

[root]# docker login -u nanjustar
Password: 
WARNING! Your password will be stored unencrypted in /root/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store

Login Succeeded

[root@iZ2zehqn8uqylq6ei48mb2Z /]# docker push nanju/diy:latest
The push refers to repository [docker.io/nanju/diy]
An image does not exist locally with the tag: nanju/diy

[root@iZ2zehqn8uqylq6ei48mb2Z /]# docker tag f41341c036a3 nanju/diy:1.0