POWERD(8)             Linux System Administrator's Manual            POWERD(8)



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. This line is meant to be
       connected to a UPS (Uninterruptible Power Supply) so that powerd 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 then
       executes 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 regularly 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 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.

       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 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.

       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@cistron.nl



                               February 14, 1994                     POWERD(8)