---
name: "power"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/power"
---

# power(4)

power button and power fail support

## NAME

**power** – power button and power fail support

## SYNOPSIS

**power0 at mainbus?**

## DESCRIPTION

HP PA-RISC machines support power failure detection in different forms:

- “soft” power button

- power failure interrupt

The **power** driver tries its best to determine the power failure condition that is a result of a power button being depressed or a power supply system failure or a similar condition. Upon detection of any of the aforementioned conditions, it tries to gracefully (if possible) shutdown the system through a call to the [boot(9)](/boot/9.md) function.

On systems equipped with the [lasi(4)](/lasi/4.md) bus adapter, we find a “soft” power button which upon depression gives us a signal in the “power register” and thus polling periodically we detect the event. Since that bit comes directly from the power button without any dampening, we perform a second long delay; thus quick transitions off and on will *not* result in a shutdown.

On modern systems, an interruption is signalled upon the power button depression and thus this avoids polling and does not require (as does being implemented in hardware) dampening.

## SEE ALSO

[intro(4)](/intro/4.md), [lasi(4)](/lasi/4.md), [pdc(4)](/pdc/4.md), [boot(9)](/boot/9.md)

## HISTORY

The **power** driver appeared in OpenBSD 3.4.