【From】 https://www.cnblogs.com/lpbottle/p/7875400.html

1. 备份原来的yum源

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

2. 下载阿里云的CentOS-Base.repo 到/etc/yum.repos.d/

curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

3. 清理缓存

sudo yum clean all

4. 生成新的缓存

sudo yum makecache