1、备份源
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
2、下载新的 CentOS-Base.repo 到 /etc/yum.repos.d/
wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
3、非阿里云ECS用户会出现 Couldn‘t resolve host ‘mirrors.cloud.aliyuncs.com‘ 信息，不影响使用，可以修改配置
sed -i -e ‘/mirrors.cloud.aliyuncs.com/d‘ -e ‘/mirrors.aliyuncs.com/d‘ /etc/yum.repos.d/CentOS-Base.repo
4、生成缓存
yum makecache
5、查看当前源
yum repolist