官方安装教程（centos) https://docs.docker.com/install/linux/docker-ce/centos/
macos 下运行 hello world出错：
$ docker run hello-world
Unable to find image 'hello-world:latest' locally
docker: Error response from daemon: Get https://registry-1.docker.io/v2/library/hello-world/manifests/latest: Service Unavailable.
See 'docker run --help'.
解决方式： 修改Daemon 的 dns设定
IIRC there were some cases where DNS resolution failed on Docker for Mac, depending on the DNS server that was configured on the host;
Can you try if it works if you set 8.8.8.8 as DNS server in the daemon configuration? You can set this by providing a JSON configuration in the preference panel (under daemon -> advanced), e.g;
{ "dns" : [ "8.8.8.8", "8.8.4.4" ]}
