In my book, the only sin worse than uselessness, is actively causing damage and waste of time.
What punishment ought to be meted then, to something that, having proven to be useless, causes untold waste of time.
Yes, NetworkManager, and nm-applet: I’m looking at you two.
Quite apart from never having quite understood what use one could have for either, I have found a number of situations in which NM has caused waste of time, only the last of which has been to prevent a KVM virtual machine I just created to connect to the network, despite all my efforts, searching on the Web, trying out countless variations on configurations and, yes, several reboots.
I have been following along the instructions given here, only to be unable to connect in UserMode, barely managing (via the Bridged interface) to connect to my host machine, and totally failing to obtain any connection to the outside world.
sudo apt-get purge network-manager network-manager-gnome
and, hey, presto, all is good and well, and I can happily connect from my guest OS to the Internet.
(see also here)
Simply changed my /etc/network/interfaces file to reflect my settings (YMMV, adjust to your LAN settings) and all works just fine:
iface lo inet loopback
iface eth0 inet dhcp
iface br0 inet static
Just remember to restart the network after you have made the changes:
sudo /etc/init.d/networking restart
Die in pain, Network Manager, and may the world be a better place without you.