1、备份安装源
cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
2、添加安装源
3、清理缓存
yum clean all
4、重新生成缓存
yum makecache
cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
yum clean all
yum makecache