CentOS 7 yum无法使用解决方法Could not retrieve mirrorlist http://mirrorlist.centos.org/?

在centos7中使用yum命令时候报错：

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"

参考这篇文章 www.cnblogs.com/kohler21/p/…