The most striking difference between Mac OS X and other flavors of Unix is in how Mac OS X handles the boot process. Gone are /etc/inittab, /etc/init.d, and /etc/rc.local from traditional Unix systems. In their place is a BSD-like startup sequence sandwiched between a Mach foundation and the Aqua user interface.
This chapter describes the Mac OS X startup sequence, beginning with the BootX loader and progressing to full multiuser mode, at which time the system is ready to accept logins from normal users. The chapter also covers custom startup items, network interface configuration, and Mac OS X’s default cron jobs.
When the computer is powered up, the firmware is in complete control. After the firmware initializes the hardware, it hands off control to the BootX loader, which bootstraps the kernel. After a trip into Mach, the control bubbles up into the BSD subsystem, and eventually into the Aqua user interface.
By default, Mac OS X boots graphically. If you’d like to see console messages as you boot, hold down ⌘-V as you start the computer. To boot in single-user mode, hold down ⌘-S as you start the computer.
BootX is located in /System/Library/CoreServices . It draws the Apple logo on the screen and proceeds to set up the kernel environment. BootX first looks for kernel extensions (drivers, also known as kexts) that are cached in the mkext cache. If this cache does not exist, BootX loads only those extensions in /System/Library/Extensions ...