Mac OS X for Unix Geeks

Chapter 7. Building the Darwin Kernel

The Darwin kernel, on which Mac OS X is based, is available in a publicly accessible CVS archive. This is not a watered-down version: you can rebuild a kernel that matches your current Mac OS X kernel in every respect. The only noticeable difference will be when you type uname -v:

Darwin Kernel Version 6.0: Sat Jul 27 13:18:52 PDT 2002;
root:xnu/xnu-344.obj~1/RELEASE_PPC

Just because you can build your kernel, does that mean you should? For most users, the answer is no, for the following reasons:

• For many users, configuring a Unix kernel involves little more than choosing and configuring device drivers. On Darwin, most devices are not in the kernel; they have their own top-level directory in the CVS archive. So, you do not need to configure Darwin to set up additional hardware support.

• Apple hardware is predictable. Most of you will be building Darwin for a G3 or G4 machine, and the range of possible chipsets is limited.

However, if you want to try installing an unofficial kernel patch, or if you want to try your hand at optimizing the kernel, then this chapter’s for you.

A Safety Net

If you have enough disk space to install two copies of Mac OS X, please do so before you start playing around with your working kernel. That way, you will have an operating system you can boot into if things go bad. (On most G3 and G4 Macintoshes, you can hold down the Option key when booting to select a boot disk.) Most importantly, your spare install of Mac OS ...