配置epel源

cd /etc/yum.repos.d/
ls
mkdir repo_bak
mv *.repo repo_bak/
到網易和阿里開源鏡像站點下載系統對應版本的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緩存
yum makecache #生成新的yum緩存
yum list|grep epel-release
yum install -y epel-release #安裝epel源
ls
#下載阿里開源鏡像的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 #驗證一下有沒有這個包