ifup em2 ##启动em2网卡时报错
Error: Connection activation failed: The connection is not for this device.
解决方法：
systemctl stop NetworkManager.service
systemctl disable NetworkManager
再启动过em2网卡，就可以了
ifup em2
ifup em2启动网卡时报错：connection activation failed
原文：http://blog.51cto.com/jschu/2096871