cd /etc/yum.repos.d/ ls mkdir repo_bak mv *.repo repo_bak/ 到网易和阿里开源镜像站点下载系统对应版本的repo文件（前提得有wget命令，yum install -y wget） wget http://mirrors.aliyun.com/repo/Centos-7.repo
wget http://mirrors.163.com/.help/CentOS7-Base-163.repo ls yum clean all #清除yum缓存 yum makecache #生成新的yum缓存 yum list|grep epel-release
yum install -y epel-release #安装epel源 ls #下载阿里开源镜像的epel源文件 wget -O /etc/yum.repos.d/epel-7.repo http://mirrors.aliyun.com/repo/epel-7.repo
yum clean all
yum makecache# yum list |grep pptpd #验证一下有没有这个包