Ubuntu causing a "CPU Fan Failed" problem on restart

[Matthew Kuiken]

Craig Hagerman wrote:
> It occured to me that most of the time the CPU IS slowed down and the
> fan is usually off. I wondered if it would make a difference if I
> tried to restart with the fan at normal full speed and the CPU working
> hard. I did a little experiment and ran a few games (Sauerbraten,
> Enemy Territory & Nexuiz) for a while to push the machine. I checked
> after and the CPU was at 55 degrees and the fan spinning at 3500 rpm.
> When I then did a restart I got no error message about the CPU fan
> failing. I waited a few minutes until the CPU was cool and the fan off
> again and restarted - and the error message game back. So I guess I am
> closer to narrowing down the problem. But just killing the sensors and
> fan control utilities doesn't seem to do anything (ie it doesn't stop
> the fan scaling).
> 
> I'll try playing around with more settings in the next few days and
> see what more I can discover about this.

While turning off the daemon that is setting the fan speed does not put 
the fan back to full power, I would bet that there is a location in the 
/proc tree that controls the fan speed.

If this is true, you might be able to put together a shutdown script 
that does (pseudo code):

Stop fan management daemon
echo "full speed setting" >> /proc/fan/control/setting spot
exit

The script would then set the fan up as if the CPU was hot, and allow 
the reboot to happen properly.  This is a somewhat hackish bug 
workaround, but it seems feasible at first blush.

Let us know what you try to fix it,
-Matt