Red Hat Enterprise Linux Installation Guide 5.2 - linux.meuhobby.com

The Kernel
following format — /boot/vmlinuz- file (where
corresponds to the kernel version specified in the boot loader's settings).
For instructions on using the boot loader to supply command line arguments to the kernel, refer
to Chapter 9, The GRUB Boot Loader. For information on changing the runlevel at the boot
loader prompt, refer Section 8, “Changing Runlevels at Boot Time”.
The boot loader then places one or more appropriate initramfs images into memory. Next, the
kernel decompresses these images from memory to /sysroot/, a RAM-based virtual file
system, via cpio. The initramfs is used by the kernel to load drivers and modules necessary
to boot the system. This is particularly important if SCSI hard drives are present or if the
systems use the ext3 file system.
Once the kernel and the initramfs image(s) are loaded into memory, the boot loader hands
control of the boot process to the kernel.
For a more detailed overview of the GRUB boot loader, refer to Chapter 9, The GRUB Boot
Loader.
2.2.1. Boot Loaders for Other Architectures
Once the kernel loads and hands off the boot process to the init command, the same
sequence of events occurs on every architecture. So the main difference between each
architecture's boot process is in the application used to find and load the kernel.
For example, the Itanium architecture uses the ELILO boot loader, the IBM eServer pSeries
architecture uses yaboot, and the IBM System z systems use the z/IPL boot loader.
2.3. The Kernel
When the kernel is loaded, it immediately initializes and configures the computer's memory and
configures the various hardware attached to the system, including all processors, I/O
subsystems, and storage devices. It then looks for the compressed initramfs image(s) in a
predetermined location in memory, decompresses it directly to /sysroot/, and loads all
necessary drivers. Next, it initializes virtual devices related to the file system, such as LVM or
software RAID, before completing the initramfs processes and freeing up all the memory the
disk image once occupied.
The kernel then creates a root device, mounts the root partition read-only, and frees any unused
memory.
At this point, the kernel is loaded into memory and operational. However, since there are no
user applications that allow meaningful input to the system, not much can be done with the
system.
To set up the user environment, the kernel executes the /sbin/init program.
2.4. The /sbin/init Program
The /sbin/init program (also called init) coordinates the rest of the boot process and
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