1.备份本地yum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 http://mirrors.aliyun.com/repo/Centos-7.repo
3.生存缓存：
yum clean all
yum makecache
4.查看yum源：
yum repolist
原文：https://www.cnblogs.com/itwlp/p/10575217.html