I'm running a fresh install of Ubuntu 12.04 Server on an abmx rack mount server. When I attempt to reboot with sudo shutdown -r now, the machine just shuts down and doesn't come back up without me manually pressing the power button.
The output of last -x,
runlevel (to lvl 2) 3.2.0-29-generic Wed Oct 31 14:32 - 14:37 (00:05)
reboot system boot 3.2.0-29-generic Wed Oct 31 14:32 - 14:37 (00:05)
shutdown system down 3.2.0-29-generic Wed Oct 31 14:30 - 14:32 (00:02)
runlevel (to lvl 6) 3.2.0-29-generic Wed Oct 31 14:30 - 14:30 (00:00)
This appears to show that the system rebooted, but it went dark (no power lights, BIOS, etc) and I had to go press the power button in order to make it boot back up. The machine does have some sort of Intel Boot Agent that usually appears before the BIOS, I'm wondering if it could be causing this. I'm not sure what information is useful for debugging this, but I put the output of lshw in http://pastebin.com/mBy72kTQ
Best Answer
Turns out the problems was related to Intel AMT and the "mei" driver (solution found here ).
Putting this into /etc/modprobe.d/blacklist.conf fixes the reboot issue,