1首先安装wget

2mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup 备份当前源

3使用wget 获取阿里yum源配置文件

        wget -O  /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo

        wget -O  /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

4 清空以前的yum 源缓存

        yum clean all

5 获取 阿里云的缓存

yum makecache