shutdown but no power off

[Michael George]

We have the firmware in our XServe set to power up on AC power restore. 
  However, this only seems to work if the power was lost with the 
machine running.  If we remove AC power after a shutdown -h, it will 
not boot w/ power restoration.

However, pull the plug on it, and it *will* boot.

Seems rather useless to me for any system on on UPS, but what do I know?

Anyway, is there a way I can have our system shutdown and halt but not 
do a power off?  It doesn't seem that shutdown itself allows this.  
Even invoking "halt" as halt will do a power off.

What's the cleanest solution to this?  I guess changing to single user 
runlevel and unmounting the filesystems and waiting for death might 
work, but I'm not even sure we could umount / with the system running...

Thanks!

-Michael