问题：

执行命令

$ docker run -it --rm -p 8888:8080 tomcat:8.5.32

报错

Unable to find image 'tomcat:8.5.32' locally
docker: 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).
See 'docker run --help'.

MAC解决问题

右键点击桌面顶栏的 docker 图标，选择 Preferences ，在 Daemon 标签（Docker 17.03 之前版本为 Advanced 标签）下的 Registry mirrors 列表中加入下面的镜像地址:

http://141e5461.m.daocloud.io

Linux

$ echo "DOCKER_OPTS=\"\$DOCKER_OPTS --registry-mirror=http://f2d6cb40.m.daocloud.io\"" | sudo tee -a /etc/default/docker
$ sudo service docker restart