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.
 Mach is a microkernel operating system developed at Carnegie Mellon University. The Mac OS X kernel, xnu, is a hybrid of Mach and BSD.