let’s Encrypt 证书之安装故障 Could not bind to IPv4 or IPv6.

Problem binding to port 80: Could not bind to IPv4 or IPv6.

则原因是 nginx 占用了80端口，输入 service nginx stop。然后再次执行证书安装命令，即可顺利安装。

安装完毕后，输入 service nginx start，重启 nginx 服务。