---
name: "mainbus"
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/mainbus"
---

# mainbus(4)

device tree root

## NAME

**mainbus** – device tree root

## SYNOPSIS

**mainbus0 at root**

## DESCRIPTION

**mainbus** provides an abstraction for all system buses to attach to. It is the start of the device tree and always attached. It is not a physical device as such, but an abstraction to which other devices may attach.

The actual buses which attach are largely machine-dependent; refer to the individual man pages for more information.

## SEE ALSO

[autoconf(4)](/autoconf/4.md), [intro(4)](/intro/4.md)