Comment 43 for bug 839595

Excerpts from ilf's message of Sun Oct 23 13:05:31 UTC 2011:
> The workaround only fixes the waiting time.
> It disables auto-up of the interface, which I want, if it us plugged in. This is a regression and still a major annoyance for me.
> Closing this bug report is not right, this isn't the fault of ifupdown, but upstart.
>

ilf, this was an intentional change in behavior and documented in the
release notes. I understand it has made your particular use case a
bit more difficult to achieve. I do see a need for a second group in
/etc/network/interfaces called something like auto-nowait that will
be brought up at boot time but not waited on. I would encourage you to
open a new bug report as a feature request for this. Its a corner case,
but one that I think we can support for you as a user. Even better, you
can probably submit a patch and we should be able to add it for 12.04.

You can achieve it yourself by changing the line in /etc/network/interfaces

from

auto eth0

to

allow-nowait eth0

and then edit /etc/init/network-interface.conf to run

ifup --allow nowait $IFACE

Just before the exec of ifup.

This will ensure that your interface is brought up, but not waited on
in the boot sequence.