下载阿里云的repo文件
centos 6:
wget http://mirrors.aliyun.com/repo/Centos-6.repo
centos 7:
wget http://mirrors.aliyun.com/repo/Centos-7.repo
cd /etc/yum.repos.d
备份旧的源
cp CentOS-Base.repo CentOS-Base.repo_2015-06-11
覆盖旧的源文件
mv Centos-6.repo CentOS-Base.repo
生成缓存
yum makecache
完工
