备份本地的yum源配置文件
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup下载对应版本repo文件, 放入/etc/yum.repos.d
以centos7为例
cd /etc/yum.repos.d/ && wget http://mirrors.163.com/.help/CentOS7-Base-163.repo
mv CentOS7-Base-163.repo CentOS-Base.repo生产缓存
yum clean all
yum makecache