对阿里云的机子也是无语了，无论用Debian 8还是Debian 9，总是出现Waiting for headers卡住不动的问题，解决办法：

删除阿里云自带了一些无用的安全源（ubuntu/debian系统）
rm -rf /root/.pip /root/.pydistutils.cfg /etc/apt/sources.list.d/sources-aliyun-0.list

然后把阿里云的官方源更换为163源，直接把下面所有的代码复制然后回车就行了

mv /etc/apt/sources.list /etc/apt/sources.list.bak && \
echo "deb http://mirrors.163.com/debian/ jessie main non-free contrib" >/etc/apt/sources.list && \
echo "deb http://mirrors.163.com/debian/ jessie-proposed-updates main non-free contrib" >>/etc/apt/sources.list && \
echo "deb-src http://mirrors.163.com/debian/ jessie main non-free contrib" >>/etc/apt/sources.list && \
echo "deb-src http://mirrors.163.com/debian/ jessie-proposed-updates main non-free contrib" >>/etc/apt/sources.list

问题解决。