背景
执行yum install xxx 时，报错
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=vag error
14: curl#6 - "Could not resolve host: mirrorlist.centos.org; Unknown error
解决方案
1，首先验证网络没问题
ping www.baicu.com
2，备份系统自带yum源配置文件
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.back
3，通过curl下载yum源
curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
4，运行yum makecache生成缓存
yum makecache
5，更新yum源，等待完成即可使用yum下载命令
yum -y update
