内网 dns dig 能解析出ip, ping 返回 Name or service not known
https://blog.csdn.net/jinyuxiaoqiang/article/details/78611430
https://blog.csdn.net/water_cow/article/details/7190880
vim /etc/nsswitch.conf
hosts: files mymachines myhostname resolve [!UNAVAIL=return] dns
hosts: files dns myhostname