Recently we were working on a Fedora 27 GNU/Linux box where we needed to completely disable the Network Manager.
Initially, we just stopped the NetworkManager service and then disabled it thinking that it would be enough.
To our surprise after we rebooted the box, we noticed that the Network Manager was active again!
After some research we found out that another service called NetworkManager-wait-online was starting the NetworkManager as some sort of recovery mechanism.
So, in order to permanently block NetworkManager from starting on boot, we disabled NetworkManager-wait-online as well.
In the end our solution to disable the NetworkManager service came down to executing the following commands as root (or using sudo):
systemctl stop NetworkManager; systemctl stop NetworkManager-wait-online; systemctl disable NetworkManager; systemctl disable NetworkManager-wait-online;
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This is an awesome hack, works on F29 also.