docker version

[root@cu-tmp-201 ~]# docker version
Client:
 Version:           18.09.6
 API version:       1.39
 Go version:        go1.10.8
 Git commit:        481bc77156
 Built:             Sat May  4 02:34:58 2019
 OS/Arch:           linux/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          18.09.6
  API version:      1.39 (minimum version 1.12)
  Go version:       go1.10.8
  Git commit:       481bc77
  Built:            Sat May  4 02:02:43 2019
  OS/Arch:          linux/amd64
  Experimental:     false

 

docker login

[root@cu-tmp-201 ~]# 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: qq
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@cu-tmp-201 ~]# cd .docker/
[root@cu-tmp-201 .docker]# ls -l
total 4
-rw------- 1 root root 169 May 19 09:19 config.json
[root@cu-tmp-201 .docker]# cat config.json
{
        "auths": {
                "https://index.docker.io/v1/": {
                        "auth": "Y29uZmlnLmpzb24="
                }
        },
        "HttpHeaders": {
                "User-Agent": "Docker-Client/18.09.6 (linux)"
        }
}