POWERD (8)
powerd \(em monitor a serial line connected to an UPS.
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 (Uninterruptible 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
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 output: 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.
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
AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl
man8/halt.8
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