参考：解决 Docker pull 出现的net/http: TLS handshake timeout 的一个办法
问题：
执行
$ sudo docker run hello-world
时出现：
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: net/http: TLS handshake timeout.
See 'docker run --help'.
原因：
不可描述。
解决办法：
使用国内的Docker仓库daocloud：
$ echo "DOCKER_OPTS="$DOCKER_OPTS --registry-mirror=http://f2d6cb40.m.daocloud.io"" | sudo tee -a /etc/default/docker
$ sudo service docker restart
解决问题：
root@ubuntu:/home/wasdns# sudo docker run hello-worldUnable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
78445dd45222: Pull complete
Digest: sha256:7820f4620e6cf3e795643fac2f6b09e7fd0a29e7e5c4eee6aac9ba0bedca158c
Status: Downloaded newer image for hello-world:latest
Hello from Docker!
This message shows that your installation appears to be working correctly.
To generate this message, Docker took the following steps:
1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
3. The Docker daemon created a new container from that image which runs the
executable that produces the output you are currently reading.
4. The Docker daemon streamed that output to the Docker client, which sent it
to your terminal.
To try something more ambitious, you can run an Ubuntu container with:
$ docker run -it ubuntu bash
Share images, automate workflows, and more with a free Docker ID:
https://cloud.docker.com/
For more examples and ideas, visit:
https://docs.docker.com/engine/userguide/
2017/2/16