转载自：https://www.jb51.net/server/345687zyo.htm
解决yum安装工具时提示以下错误信息
已加载插件：fastestmirror, langpacks
Loading mirror speeds from cached hostfile
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was
14: curl#6 - "Could not resolve host: mirrorlist.centos.org; 未知的错误"
首先确保虚拟机网络畅通
ping www.baicu.com
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
通过curl下载yum源
curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
运行yum makecache生成缓存
yum makecache
更新yum源，等待完成即可使用yum下载命令
yum -y update