---
name: "powerd"
section: "8"
platform: "linux"
package: "sysvinit"
version: "2.71-2"
release: "Debian 1.3 (Bo)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/powerd/8"
---

# 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. 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)](/init/8.md) 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 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.**

  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)](/shutdown/8.md), [init(8)](/init/8.md), [inittab(5)](/inittab/5.md).

## AUTHOR

Miquel van Smoorenburg, miquels@cistron.nl