The Linux Operating System

R.Bigelow

What is an Operating System

An operating system is a collection of programs that manage a computer's resources.

Typical management tasks include, task scheduling, storage allocations, memory management, and peripheral interfacing.

Operating System Model

UserApplicationsSystem ProgramsKernelDevice DriversDevices

User interacts with applications and system programs.System programs interact with the user, applications and Kernel.Kernel interacts with system programs and device drivers.Device drivers interact with the kernel and devices

Linux Boot Sequence

POSTHW BOOT LOADERSW BOOT LOADERKERNELINITRC Startup ScriptsGETTYUser Login

POST

The Power On Self Test occurs every time the computer is started. During this test memory is verified, fixed disks and peripheral cards are identified.

The POST routine is completed by the BIOS (Basic Input/Output System) code.

Boot Loader

The BIOS code contains the Hardware (HW) boot loader. The primary responsibility of the HW boot loader is to identify the boot order of devices, and to locate the boot signature of the software (SW) boot loader

The job of the SW boot loader is to load the Kernel of the operating system.

GRUB

The Grand Unified Bootloader (GRUB) is the most commonly used boot loader in newer distributions of Linux. GRUB is able to load any operating system that is supported by the computer's architecture.

GRUB is also capable of presenting users with a graphical menu, which allows them to select which operating system they wish to load.

GRUB ConfigurationA

ll of the configuration for GRUB is done in the /boot/grub/menu.lst file. Below are some sample lines from this file.

Splashimage= XXX Specifies the background image

default=N – Specifies the default operating system to load.

timeout=N - Specifies the amount of time to wait before loading the default OS.

Sample Linux GRUB Entry

title Fedora Core (2.6.18-1.2849.fc6) root (hd0,3)kernel /boot/vmlinuz-2.6.18-1.2849.fc6 ro rhgb quiet initrd /boot/initrd-2.6.18-1.2849.fc6.imgsavedefaultboot

Sample Windows Grub Entry

title Windows Vista Businessroot (hd0,0)savedefaultmakeactivechainloader +1

The Linux Kernel http://kernel.org/

The kernel is common to all distributions and is constantly being updated, by thousands of developers.

The kernel can be stored in any location, but it can gernally be found in the /boot directory. Typical kernel filename would be something like: vmlinuz-2.6.17-10

All Linux kernels for the last 15 years have been version 2.

Kernel Version numbering2.B.C-D

B This number represents the major version number, thus far revisions to the 2 kernel have been 0,2,4 and 6. Odd major versions numbers represent development kernels.

C- This is the minor version number. Typically a new minor versions is released every 2-6 months.

D- Revision number, this represents minor bug fixes and performance tweaks, and is updated almost weekly.