Spontaneous Shutdowns

[Brian Mayton]

I have a PowerMac G4 running YDL 3.0 as a web server.  While it's up 
and running, it works great.

While I was setting it up everything went smoothly.  I did more or less 
a default server install.  However, while I was setting it up, I never 
left it on longer than I was working with it; when I was done I would 
turn it off.

Now that it's in place and running as a web server, it's been doing 
something strange - after about five days, it just shuts off.  It 
doesn't crash or anything, when I go to reboot it, it's just sitting 
there as if someone had pulled the cord or held the power button for a 
few seconds.  After starting it back up again, there's nothing in the 
system logs to suggest that it was ever shut down.  In a normal 
shutdown there are all kinds of messages that are logged as processes 
shut down, and there's always a line that says something like "System 
going down for shutdown".  When I look at the logs for when this is 
happening, there is nothing like that.  There are usually a couple of 
messages about people logging into the FTP server, stuff like that, and 
then the stuff that gets logged during startup.

Is there any way that someone could be doing this from a command line 
if they had the root password?  As far as I can tell, there isn't any 
way to shut down Linux without logging messages short of pulling the 
plug.

This machine *is* on a working UPS.  The only explanations for this 
that I can come up with for this are either that there's some bizarre 
kernel bug that's causing it to shut down, or that someone's actually 
pulling the plug on it.

Does anyone here have any guesses as to what might be happening?

The machine is a PowerMac G4 with somewhere around 640MB RAM and a pair 
of 120 GB drives with Yellow Dog 3.0.  I can't remember the exact specs 
(and I can't get them now since the machine is down) but I do remember 
that it looks like the original G4s with the pinstripe pattern, and it 
has an internal firewire port on the motherboard.  It's either 450 or 
500 MHz. This is the second machine I've tried (with the same hard 
disks and installation of YDL).  The first one was also a G4, but was 
lacking the internal firewire port.  Both machines did the spontaneous 
shutdown thing.

Thanks in advance,
Brian