Comment 32 for bug 497299

I added the

auto lo
iface lo inet loopback

lines to /etc/network/interfaces file to one of the two server machines (still no access to the other one, one day downtime now...): now the services are starting up normally at boot -- but network manager disappeared from the control panel (NM service started and network working anyway...)

Nevertheless, I consider this as a workaround. Before modifying "interfaces", localhost interface was correctly set up anyway; moreover, if upstart now really requires these two lines in "interfaces", then this should be done automatically, or the user be warned.