Chapter 11: Basic Kernel Configuration

Overview

Kernel, not colonel!
This is blowfish, not chicken.
Less grease, more function.

Depending on your experience level, the "kernel" is either the subject of great mystery, something you reconfigure whenever the whim strikes you, or something you know to leave well enough alone. In a commercial operating system, such as Microsoft Windows or Sun Microsystems' Solaris, the systems administrator doesn't touch the kernel.

In some open-source operating systems, such as Linux or FreeBSD, rebuilding the kernel is recommended on any number of occasions. OpenBSD falls somewhere in the middle: The standard kernel is meant to be perfectly usable without modification, but you have tools to perform any tweaks or renovations desired. Additionally, you get the complete set of source code and kernel-building tools in case you need to perform wholesale kernel surgery.

The OpenBSD kernel can be dynamically modified, in most cases even while the system is fully functioning, via sysctl(8). We cover that in detail. Some hardware requires special tweaks in the kernel to run correctly on OpenBSD. We'll describe how those adjustments can be made with config(8) and how this same technique can be used to alter general kernel parameters.