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From: bks@ALFA.berkeley.edu (Brad Sherman)
Newsgroups: comp.unix.questions
Subject: Re: Followup to: UPS initiated autoshutdown
Keywords: UPS, blackout, daemon
Message-ID: <26532@agate.BERKELEY.EDU>
Date: 20 Jul 89 18:07:52 GMT
References: <216@tnl.UUCP> <1989Jul9.193016.9426@ddsw1.MCS.COM> <462@cals01.NEWPORT.RI.US> <217@tnl.UUCP>
Sender: usenet@agate.BERKELEY.EDU
Reply-To: bks@alfa.berkeley.edu (Brad Sherman)
Organization: University of California, Berkeley
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In article <217@tnl.UUCP> norstar@tnl.UUCP (Daniel Ray) writes:
>B. Long duration blackouts (2% likely here in Burlington). The power goes out
>and stays out for at least 20 minutes. The system senses the failure via a
>test thru a serial port every minute. Users are warned, and the daemon waits
>to retest after another minute. Meanwhile, the UPS is switched to battery
>power. The daemon tests again, finds power still out, so starts the auto-
>shutdown sequence, leading to shutdown 60 seconds later. Now the system is
>down, but not turned off physically. Battery power continues to drain, until
>after 10-20 minutes the UPS shuts off power to prevent the battery from
>being overdrained. This shuts off the CPU. Sometime later, power is restored.
>The system restarts as from a power off condition, reboots, and is up. The
>UPS slowly recharges its battery, but this takes hours. The weakness is that
>a second power failure would occur, and that the system would not have the
>minimum 2-3 minutes required for shutdown, causing a crash. If the system
>knew that it just came up from a power failure, it could change the daemon
>to use 'haltsys' at the first sign of a second blackout. After say a day,
>it could go back to the normal 2 minute cycle. (This also demonstrates the
>wisdom of using only a very short waiting period between when the daemon
>senses an outage and when it starts a shutdown. I think 1 minute is good,
>so that a second power failure with a partially recharged UPS battery might
>last long enough for system shutdown).

When I was setting up business systems in Lafeyette, CA which has
brownouts when the humidity hits 70% and blackouts when the first
drop of water touches a PG&E transformer the rule of thumb was:

	After a power outage, do not restart the computer until
	power has been restored for a length of time equal to
	the length of the outage.

An empirical result dealing with outage "bursts."

Hearsay alert: I remember being  told that a UPS, which does an excellent job
of conditioning the power for the machine hanging off it can wreak havoc upon
power for other machines on the same main circuit (but not on the UPS).

		-- Brad Sherman(bks@ALFA.Berkeley.EDU)
---------

Not only do the opinions expressed herein not represent those of
the Regents of the University of California, but by the time you
read this they probably won't represent mine.