ref:
https://docs.docker.com/engine/installation/linux/ubuntulinux/#/install-the-latest-version
ps: if you want to use proxy in bash, type
export http_proxy="http://username:password@IP:Port"
ref: http://blog.csdn.net/zxncvb/article/details/42774987
原文：http://www.cnblogs.com/pdev/p/6260257.html