Network Manager Hell
I recently re-installed my laptop (which has loopback, WIFI and wired network connections) from scratch and I found that it has "NetworkManager is not running" displayed when I click the NetworkManager applet, which is apparently not that strange. This was straight after an install which was disappointing :-(
My installation method for my laptop comes from an Ubuntu 14.04 Server base with some desktop components. The reason for this is that I have switched to OpenBox which is lovely compared to Unity and I don't run into the bugs I always do when customising XFCE... it's also lightning fast. Unfortunately sometimes because of this it's a bit difficult to google for answers...
If I installed the desktop version of Ubuntu I believe it will let you use the the WIFI when installing (which is very nice) however when you install the server edition there is no prompt for wifi and I ended up plugging in a cable for the installation, this left my /etc/network/interfaces looking like the following:
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
auto eth0
iface eth0 inet dhcp
Which is pretty reasonable and correct... however this configuration causes NetworkManager to not start, or at least be disabled... You need to remove all the lines which reference eth0 and then NetworkManager will start properly!
Pretty surprised at this, as I have three network devices. Surely I've just gone down from 2 network devices being managed by /etc/network/interfaces to one, so I don't understand why NetworkManager would refuse to start and manage my WIFI in both cases...