Network Manager says device unmanaged in Ubuntu

There have been a lot of complaints about the Network Manager showing “device is unmanaged” problem. There are a lot of bugs posted which concern this problem. I don't exactly know how or why this occurs?? But I can probably give a small explanation and solution to the problem.

Most of the times the reason behind this problem is the changes in the /etc/network/interfaces file. These changes could either be done manually or by some program ( running pppoeconf in terminal). Such changes in this file, when done, create confusion for Network Manager. And after looking at them Network manager thinks that we are handling the connections or a particular interface manually and so it backs off. This is the reason why it shows Device is unmanaged.

So, if you are facing this problem then first of all you should take a look at your /etc/network/interfaces file. It should look something like this

auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp

Actually now a days in the newer versions of Ubuntu only loopback (lo) interface is visible. Rest of the interfaces are managed by Network manager in other files. Well you would be surprised to know that Network manager manage our connection configuration files in ~/.gconf/ folder :P.

This solution has worked for most of the people. If you are still in trouble, have another fix or there is something I should add/change here then feel free to leave a comment.