Red Hat Enterprise Linux - IBM N Series Hardware Manual

Linux boot process
This section is an overview of the Linux boot process in an x86 environment. In general, the
boot process is as shown in Figure 18-47.
Figure 18-47 Linux boot process
System BIOS
The process starts when you power up or reset your System x. The processor runs the basic
input/output system (BIOS) code, which then runs a power-on self-test (POST) to check and
initialize the hardware. It then locates a valid device to boot the system.
Boot loader
If a boot device is found, the BIOS loads the first stage boot loader stored in the master boot
record (MBR) into memory. The MBR is the first 512 bytes of the bootable device. This first
stage boot loader is then run to locate and load into memory the second stage boot loader.
Boot loaders are in two stages because of the limited size of the MBR. In an x86 system, the
second stage boot loader can be the Linux Loader (LILO) or the GRand Unified Bootloader
(GRUB). After it is loaded, it presents a list of available kernels to boot.
OS kernel
After a kernel is selected, the second stage boot loader locates the kernel binary and loads
into memory the initial RAM disk image. The kernel then checks and configures hardware and
peripherals, and extracts the initial RAM disk image into load drivers and modules needed to
boot the system. It also mounts the root device.
Continue system start
After the kernel and its modules are loaded, a high-level system initialization is run by the
/sbin/init program. This program is the parent process of all other subsequent start
processes. /sbin/init runs /etc/rc.d/rc.sysinit and its corresponding scripts. This
process is followed by running /etc/inittab, /etc/rc.d/init.d/functions, and the
appropriate rc directory as configured in /etc/inittab. For example, if the default runlevel in
/etc/inittab is configured as runlevel 5, /sbin/init runs scripts under the
/etc/rc.d/rc5.d/ directory.

Red Hat Enterprise Linux 5.2

Install
The installation process explained here assumes that the server does not have any special
hardware (SCSI card or HBA) that would require a specific Linux driver. If you have a device
driver you need to load during the installation process, type Linux dd at the installation boot
prompt. Type this before the installation wizard is loaded.
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Chapter 18. Boot from SAN