yum repolist # 查看yum源列表
yum localinstall http://dl.fedoraproject.org/pub/epel/7/x86_64/Packages/e/epel-release-7-11.noarch.rpm -y
yum makecache # 将服务器上的软件包信息下载到本地缓存, 以提高搜索和安装软件的速度
yum repolist # 可以再次查看新加入的列表
yum install pptpd -y # 再次执行安装pptpd
------------------------------------或
yum install -y http://dl.fedoraproject.org/pub/epel/7/x86_64/Packages/e/epel-release-7-11.noarch.rpm