Boot Sequence of Linux

Linux Boot Sequence:
Reboot/Poweron --> SMPS(Switched mode powersupply) --> Processor --> BIOS --> MBR(MasterBootRecord) --> GRUB/LILO ---> /etc/inittab --> /etc/motd
Reboot/Poweron --> Switch on or reboot the system
SMPS(Switched mode power supply)--> It is an electronic power supply that incorporates a switching regulator in order to be highly efficient in the conversion of electrical power.An SMPS is usually employed to efficiently provide a regulated output voltage, typically at a level different from the input voltage.
Processor --> the unit that reads and executes program instructions.
BIOS (Basic Input Output System) --> The BIOS software is built into the PC, and is the first code run by a PC when powered on. The primary function of the BIOS is to load and start an operating system.It Will initialize POST and Bootable Media devices
POST- Power On self test --> It will check whether all the peripheral devices are properly connected.
Bootable Media Devices --> It will check the bootable devices like cdrom etc are connected properly.
MBR(Master Boot Record)--> It is first sector of first partition which will initiate GRUB/LILO.It is 512 bytes (446byte for Executable codes and logmessages,64 bytes for Partition table information,2 bytes for Magic number).On 446 bytes loads the Kernel and initrd,64 bytes is divided into 4 Partition by defaultm in which first 3 are primary partition and 1 for Extendable partition.MBR uses virtual filesystem called NASH file systems from MBR to GRUB
/boot is an active partition or primary partition.
MBR will load the secondary boot loader which loads GRUB/LILO
LILO --> Linux loader , boot loader which has several limitation while booting so it is not used instead GRUB is used
GRUB --> Grand Unified Bootloader, which holds the address of kernel and initrd (path: /boot/grub/grub.conf)
/etc/initrd - contains required module to boot
/etc/inittab --> to indicate in which run level it should initialize
Runlevel -->
0 - halt
1 - Single user mode
2 - Multiuser mode without NFS
3 - Multiuser mode with NFS
4 - Not used
5 - GUI
6- Reboot
(All Run level specification module are defined in /etc/rc/)
/etc/rc.local --> It will be used in run day jobs or scripts after booting
/etc/motd - To set message of the day.

Link to GNU/Linux pre-installation checklist

Pls follow the below link for preinstllation checklist
http://algolog.tripod.com/lnxchk.htm

Linux: The Basics

Linux is an operating system that can be downloaded free and "belongs" to an entire community of developers, not one corporate entity. In other words, anyone from professional software developers to hobbyist computer hackers can access and make changes to the Linux kernel—all the information about Linux is open and available to everyone. That's why Linux is known as "open source" or "free software," because there is nothing secret about this system. This freedom also allows companies to sell and distribute Linux on CD-ROM or by other means, although those companies must keep their code open to the public.
With more and more people looking for an alternative to Windows, Linux has recently grown in popularity and is quickly becoming a favorite among major corporations and curious desktop users. Not only does it give users a choice of operating systems, it also proves itself valuable with its power, flexibility, and reliability.

How did Linux get started

The concept of open source programming has been around for many years—its roots stem from universities that needed to be able to share information as well as allow students and developers to adapt programs to meet their needs. In 1984, Richard Stallman, a researcher at the MIT AI Lab, started a project he called GNU to counter the fast-moving trend toward proprietary, fee-based software. Stallman, who remains an open advocate of open source, believes that making source code available to anyone who wants it is integral to furthering computer science and innovation.
This concept served as the basis of Linux development, the brainchild of Linus Torvalds. When Torvalds began developing Linux in 1991, he was a student at the University of Helsinki and originally targeted Linux at the Intel 386 (although it is now one of the most widely ported operating systems available for PCs). Torvalds wanted to write a new version of UNIX, so he and a group of programmers combined talents and created a core operating system called Linux.

Introduction to Linux

Linux is no longer only for hobbyist hackers who dig so deep into computer code that it gets caught under their fingernails like gardening soil. With the success of a growing number of companies like Red Hat that develop and package open source programs, Linux has found its way onto the servers and desktops of major corporations as well as personal computers. It offers one of the most powerful and reliable systems available—and as an open source system, it can be altered to meet the needs of its users.

Welcome to Knowledge Share Repository

Hi Folks,
I am Saravana
On behalf of my blogspot, I cordially Welcome you all to ishare knowlegde repository.
In this blogspot we will share our knowledge in Technical aspect mostly in Linux ,Xenserver,Xenapp,Storage
Here we will be sharing knowledge such as templates of any shell scripting, troubleshooting on linux .., etc..
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Saravana