1、备份
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
或者
curl -o /etc/yum.repos.d/CentOS-base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
3、运行 yum makecache 生成缓存
