备份默认源文件

进入yum.repos.d文件夹

cd /etc/yum.repos.d/

mv CentOS-Base.repo CentOS-Base.repo.backup

下载yum源

网易源

wget http://mirrors.163.com/.help/CentOS7-Base-163.repo

阿里源

wget http://mirrors.aliyun.com/repo/Centos-7.repo

更新yum

生成缓存

yum makecache