Comment 87 for bug 1301015

Ubuntu 14.04 Server Not Rebooting (ifupdown network issue)

It appears that with the latest bundle of Ubuntu updates, ifupdown breaks the server boot quite fantastically.

Resolution 1: Change the order that the updates are applied in

[1] BACKUP SERVER!
[2] apt-get update
[3] apt-mark hold ifupdown
[4] apt-get upgrade -y
[5] apt-mark unhold ifupdown
[6] apt-get upgrade -y
[7] Check that the server reboots correctly

Resolution 2: edit your network interfaces file, specifically looking for incorrect commands:
example: post-up ip6tables-restore < /etc/iptables.up.rules

This is clearly not correct since it is attempting to load IPV4 tables to IPV6 routes and will result in a network failure,
thus preventing booting of the server.

[1] nano /etc/network/interfaces
[2] Remove incorrect post boot commands, ie. post-up ip6tables-restore < /etc/iptables.up.rules
[3] apt-mark unhold ifupdown (If you previously had the package on hold)
[4] apt-get upgrade -y
[5] Check that the server reboots correctly.

I am not sure where this bug came from @ubuntu but it is nasty, nasty, nasty!