背景：CentOS安装后无法上网，解决方案如下：

When you install CentOS with the GUI installer, is very easy to miss the configuration part where you make able the network interface to be bringed up when the system boots.

You have to edit /etc/sysconfig/network-scripts/ifcfg-YOUR_NIC_NAME, and specifically this:

ONBOOT=yes

next time you will boot the server, the NIC should be up.