Summary

This chapter described what happens between power on and kernel bootup. We discussed what BIOS and Open Firmware are and how they interact with the kernel bootloaders. We discussed LILO, GRUB, and Yaboot as some of the more commonly used bootloaders. We overviewed how they work and how they call up the first kernel initialization routines.

We also went through the functions that make up kernel initialization. We traversed the kernel code through its initialization process, touching on concepts that were introduced in previous chapters. More specifically, we traced the Linux kernel initialization through the following high-level operations:

• Starting and locking the kernel

• Initializing the page cache and page addresses for memory management in Linux

• Preparing multiple CPUs

• Displaying the Linux banner

• Initializing the Linux scheduler

• Parsing the arguments passed to the Linux kernel

• Initializing the interrupts, timers, and signal handlers

• Mounting the initial filesystems

• Finishing system initialization and passing control out of init and back to the system

As we leave kernel initialization, we must mention that, at this point, the kernel is functional and begins to start many higher level Linux applications, such as X11, sendmail, and so on. All these programs rely on the basic configuration and setup that we have just outlined.