首先安装wget
    yum install wget -y
    将系统原始配置文件失效
    mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
    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.r
    epo
    wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.r
    epo
    清空以前yum源的缓存
    yum clean all
    获取阿里云的缓存
    yum makecache