ubuntu18.04和centos/.7.1908镜像下载地址

阿里云官方镜像站：https://developer.aliyun.com/mirror/

ubuntu18.04：http://mirrors.aliyun.com/ubuntu-releases/18.04/

centos/.7.1908：http://mirrors.aliyun.com/centos/7.7.1908/isos/x86_64/