Chapter 1. Boot Process,
Init, and Shutdown
An important and powerful aspect of Red Hat Enterprise Linux is
the open, user-configurable method it uses for starting the
operating system. Users are free to configure many aspects of the
boot process, including specifying the programs launched at
boot-time. Similarly, system shutdown gracefully terminates
processes in an organized and configurable way, although
customization of this process is rarely required.
Understanding how the boot and shutdown processes work not only
allows customization, but also makes it easier to troubleshoot
problems related to starting or shutting down the system.
Below are the basic stages of the boot process for an x86
system:
-
The system BIOS checks the system and launches the first stage
boot loader on the MBR of the primary hard disk.
-
The first stage boot loader loads itself into memory and
launches the second stage boot loader from the /boot/ partition.
-
The second stage boot loader loads the kernel into memory, which
in turn loads any necessary modules and mounts the root partition
read-only.
-
The kernel transfers control of the boot process to the
/sbin/init program.
-
The /sbin/init program loads all
services and user-space tools, and mounts all partitions listed in
/etc/fstab.
-
The user is presented with a login screen for the freshly booted
Linux system.
Because configuration of the boot process is more common than
the customization of the shutdown process, the remainder of this
chapter discusses in detail how the boot process works and how it
can be customized to suite specific needs.
