Linux slow shutdown

My linux mint mate 17 was taking a long time to shut down. To discover what the problem was I used

sudo halt
and then give it plenty of time. eventually it will say “system halted”. The messages above that will tell me what took so long.

modem manager is taking a long time to close a remote connection. Here’s how to stop that:

In my case replacing line:
stop on stopping dbus
into:
stop on runlevel [06]
into the file /etc/init/network-manager.conf
fixes this problem.

But it may be necessary to include these changes:

open /etc/init/network-manager.conf

Just before “stop on stopped dbus” add the line

kill timeout 1

open /etc/init/modemmanager.conf

Just before “stop on stopped network-manager” add the line

kill timeout 1