docker拉取MySQL镜像，提示无法连接Got permission denied while trying to connect to the Docker daemon socket at unix

报错内容：

Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.40/images/search?limit=25&term=mysql: dial unix /var/run/docker.sock: connect: permission denied

解决方法：