安装certbot-auto就是被各种折腾
好不容易来到这一步：
Reading package lists... Done
Building dependency tree
Reading state information... Done
dialog is already the newest version.
gcc is already the newest version.
python is already the newest version.
python-dev is already the newest version.
ca-certificates is already the newest version.
libssl-dev is already the newest version.
augeas-lenses is already the newest version.
libaugeas0 is already the newest version.
libffi-dev is already the newest version.
python-virtualenv is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
Creating virtual environment...
Installing Python packages...
然后就是被卡住了，经过各种查找，一个比较靠谱的说法是：内存不够了！
会产生这种错误：
x86_64-linux-gnu-gcc: internal compiler error: Killed (program cc1)
于是， 我关闭了各种我能够控制的程序，然后根据大神的说明做如下处理：
sudo dd if=/dev/zero of=/swapfile bs=1024 count=524288
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
这种方法，下载原程序安装时通过，直接运行还在等待中。
终于成功了，安装过程中发现要做好几个问题：
1.你的内存要够用，否则，会出现 gcc报错；
2.pip的源，要换国内的，要用https的，否则会报警，也很烦；
3.先安装依赖，我是用源码安装的，python setup.py install，然后再./certbot-auto
4.出现Installing Python packages...后，可能要等很长时间，太长了就中断重新再来。
5.ubuntu版本低了就不好安装，最好16版本的，直接apt-get安装。