如果你的docker pull或者docker search操作老报超时问题，按网上说的改daemon.json或改什么resove.conf，hosts，改了之后还是不行，不妨直接实施用阿里云的指定仓库拉取，拉取前需要先docker log in 阿里云的账户，亲测有效，搞了好几个小时
sudo docker pull registry.cn-hangzhou.aliyuncs.com/acs-sample/jenkins
附可能会报的问题：
Get "https://registry.cn-hangzhou.aliyuncs.com/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
Error response from daemon: Get "https://registry-1.docker.io/v2/": read tcp 10.42.71.121:56040->198.44.185.131:443
Error response from daemon: Get "https://registry-1.docker.io/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
另外还可以直接用这个https://github.com/DaoCloud/public-image-mirror pull就行，search还是不行