Configure rsh access for the IP/user of your sun and make a crontab that runs:
$ rsh <filer> halt
Using "rsh" might be a good idea(security concerns apart), i am not sure about your "crontab" suggestion though.
Instead if you have Smart-UPS from APC, it comes with s/w that can be used to shutdown Suns. There is also software for linux boxes.
I would put a script in /etc/rc3.d called KxxShutDownNetApp (K subscript would ensure that this runs only when the machine is being shutdown) make sure that the script runs only when shutdown because of Power Loss and not EVERYTIME the machine is shutdown.
Put rsh filer halt in that script.
HTH
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