powerd
Hurricane Electric Internet Services
NAME
powerd -- monitor a serial line connected to an UPS.
SYNOPSIS
/sbin/powerd serial-device
DESCRIPTION
Powerd is a daemon process that sits in the background and
monitors the state of the DCD line of the serial device.
It is meant that this line is connected to an UPS (Unin-
terruptible Power Supply) so that it knows about the state
of the UPS. As soon as powerd senses that the power is
failing (it sees that DCD goes low) it notifies init(8)
and init will execute the powerwait and powerfail entries.
If powerd senses that the power has been restored, it
notifies init again and init will execute the powerokwait
entries.
ARGUMENTS
serial-device
Some serial port that is not being used by some
other device, and does not share an interrupt with
any other serial port.
DIAGNOSTICS
Powerd regulary checks the DSR line to see if it's high.
DSR should be directly connected to DTR and powerd keeps
that line high, so if DSR is low then something is wrong
with the connection. Powerd will notify you about this
fact every two minutes. When it sees that the connection
has been restored it will say so.
HOWTO
It's pretty simple to connect your UPS to the Linux
machine. The steps are easy:
1. Make sure you have an UPS with a simple relais out-
put: it should close its connections (make) if the
power is gone, and it should open its connections
(break) if the power is good.
2. Buy a serial plug. Connect the DTR line to the DSR
line directly. Connect the DTR line and the DCD line
with a 10 kilo ohm resistor. Now connect the relais-
output of the UPS to GROUND and the DCD line. If you
don't know what pins DSR, DTR, DCD and GROUND are you
can always ask at the store where you bought the
plug.
3. You're all set.
BUGS
Well, not a real bug but powerd should be able to do a
broadcast or something on the ethernet in case more Linux-
boxes are connected to the same UPS and only one of them
is connected to the UPS status line.
SEE ALSO
shutdown(8), init(8), inittab(5).
AUTHOR
Miquel van Smoorenburg, miquels@drinkel.ow.org
Hurricane Electric Internet Services
Copyright (C) 1998
Hurricane Electric.
All Rights Reserved.