SIGPWR signal in system v

[Dennis S. Breckenridge]

ohurley at cs.tcd.ie (Oisin Hurley) writes:

>1. When power goes, is this signal sent to every process currently running?

No, only processes that list for it. Init is one of those processes.

>2. How far does the power have to drop before the signal is activated?

Specs say that a frequency change of 5hz or a voltage level out of the 
specified voltage (on a 3B2 its about 92 volts).

>3. How long does the power have to stay at that level to ensure activation?
>	(how about transients, etc.)

If the frequency changes, it is a very good sign that you are really going
to have a power failure. With the tolerance in the power supply, 94-130 
volts, anything outside that range is a real drop. Once the signal is caught
init start's the shutdown process. 

>4. Is the signal generated on the mboard or is there a line from the psu?

The power supply is responsible.

>5. Has anybody used it - is it useful? Is there enough time to sync disks
>   upon receipt of SIGPWR (I presume there's hardly time for anything)?
>   
>6. Why is it there?

The 3B2 series of machines use the power on off switch to send this signal.
Other than that, I don't know. I have considered tying my UPS alarm into
this bit and shuting down the system if the power drops. Yuor right about
the time. If the disks could write fast enough, UNIX could shut down grace-
fully. 
-- 
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    Dennis S. Breckenridge VE7TCP at VE7TCP [44.135.160.59]  dennis at nebulus.UUCP
Lately it occurs to me...what a long strange trip it's been. - Grateful Dead
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