1. Remove Network Manager from startup Services.
#chkconfig NetworkManager off
2. Add Default Net Manager
#chkconfig network on
3.Stop NetworkManager first
#service NetworkManager stop
4.and then start Default Manager
#service network start
Bringing up interface eth0: Error:Connection activation failed:Device not managed by NetworkManager
原文：http://www.cnblogs.com/hxsyl/p/6018788.html