.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 Powerdis a daemon process that sits in the background and monitors the stateof the DCD line of the serial device. This line is meant to beconnected to a UPS (Uninterruptible Power Supply) so that \fBpowerd\fP knowsabout the state of the UPS. As soon as \fBpowerd\fP senses that thepower 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\fPagain and \fBinit\fP will execute the \fBpowerokwait\fP entries..SH ARGUMENTS.IP serial-deviceSome serial port that is not being used by some other device, and does notshare 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\fPkeeps that line high, so if \fBDSR\fP is low then something is wrongwith the connection. \fBPowerd\fP will notify you about this fact everytwo minutes. When it sees that the connection has been restored itwill say so..SH HOWTOIt's pretty simple to connect your UPS to the Linux machine. The stepsare easy:.TP 0.5i.B 1.Make sure you have an UPS with a simple relay output: it shouldclose its connections (make) if the power is gone, and it shouldopen 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\fPresistor. Now connect the relay output of the UPS to GROUNDand the DCD line. If you don't know what pins DSR, DTR, DCD andGROUND are you can always ask at the store where you bought the plug..TP 0.5i.B 3.You're all set..SH BUGSWell, not a real bug but \fBpowerd\fP should be able to do a broadcast orsomething on the ethernet in case more Linux-boxes are connected tothe 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 AUTHORMiquel van Smoorenburg, miquels@cistron.nl