問題描述：
一個新裝的centos 系統,想用yum下載軟件提示錯誤
Loaded plugins: 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; Unknown error"
懷疑是DNS配置的問題，于是ping了百度發現果然 ping不通
ping www.baidu.com
ping: www.baidu.com: Name or service not known
問題解決：
用vim打開文件 resolv.conf
vim /etc/resolv.conf
在其中增加DNS配置
nameserver 8.8.8.8
nameserver 114.114.114.114
