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'\" -*- coding: UTF-8 -*-
.\" Copyright (C) 1994 Miquel van Smoorenburg.
.\"
.\" This program is free software; you can redistribute it and/or modify
.\" it under the terms of the GNU General Public License as published by
.\" the Free Software Foundation; either version 2 of the License, or
.\" (at your option) any later version.
.\"
.\" This program is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public License
.\" along with this program; if not, write to the Free Software
.\" Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
.\"
.TH POWERD 8 "Feb 14, 1994" "" "Linux System Administrator's Manual"
.SH NAME
.\" powerd \(em monitor a serial line connected to an UPS.
powerd -- monitor a serial line connected to an UPS.
.SH SYNOPSIS
.B /sbin/powerd
.RB " serial-device "
.SH DESCRIPTION
.B Powerd
is a daemon process that sits in the background and monitors the state
of the DCD line of the serial device. This line is meant to be
connected to a UPS (Uninterruptible Power Supply) so that \fBpowerd\fP knows
about the state of the UPS. As soon as \fBpowerd\fP senses that the
power is failing (it sees that DCD goes low) it notifies \fBinit\fP(8),
and \fBinit\fP then executes the \fBpowerwait\fP and \fBpowerfail\fP entries.
If \fBpowerd\fP senses that the power has been restored, it notifies \fBinit\fP
again and \fBinit\fP will execute the \fBpowerokwait\fP entries.
.SH ARGUMENTS
.IP 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.
.SH DIAGNOSTICS
\fBPowerd\fP regularly checks the \fBDSR\fP line to see if it's high.
\fBDSR\fP should be directly connected to \fBDTR\fP and \fBpowerd\fP
keeps that line high, so if \fBDSR\fP is low then something is wrong
with the connection. \fBPowerd\fP will notify you about this fact every
two minutes. When it sees that the connection has been restored it
will say so.
.SH HOWTO
It's pretty simple to connect your UPS to the Linux machine. The steps
are easy:
.TP 0.5i
.B 1.
Make sure you have an UPS with a simple relay output: it should
close its connections (make) if the power is gone, and it should
open its connections (break) if the power is good.
.TP 0.5i
.B 2.
Buy a serial plug. Connect the DTR line to the DSR line directly.
Connect the DTR line and the DCD line with a \fB10 kilo ohm\fP
resistor. Now connect the relay 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.
.TP 0.5i
.B 3.
You're all set.
.SH BUGS
Well, not a real bug but \fBpowerd\fP 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.
.SH SEE ALSO
.BR shutdown (8),
.BR init (8),
.BR inittab (5)
.SH AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl
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