BIOS-MBR-BOOT LOADER– Kernel-Init -Run Level
1) BIOS it will load the MBR into the Memory From the Boot Sector ( Boot sector it will be floppy ,Hard Disk , Cdrom. These Boot load priority it will be change from the BIOS Setup)
2)Then Boot Loader It will take the control of the system From the following file /etc/lilo.conf /etc/grub.conf (LILO is most Linux Distribution Default Boot Loader) [ linux it will load the image windows it will load the Dos].Details about /etc/grub.conf file Refer This Link.
3)It will show the list of Operating System which one need to boot. It will identify which kernel needs to boot.
System Startub
Linux Loads the kernel & initrd(initial RAM disk) image into system memory to boot the system .
Since kernel is the first program, this process id is 1 and it will mount the root file system.
Then initrd is used by kernel as temporary root file system,untill kernel booted with real root file system.This initrd has necessary files like driver,library,binary files to access the hard disk to boot the operating system initally.
4)Then Kernel run init (initialization) program according to the /etc/inittab.
Under the /etc/inittab file it has Run level script
Example : /etc/rc.d/rc0.d
Just like it has the Linux Six Run level
Under the run level
If File start With
K-Shutdown Script
S-Start Up Script
5)Based on the default run level it will executed the process.Study about Run Level Refer these Link
Important files For Linux Boot Sequence
Boot loader
/etc/grub/grub.conf
/etc/lilo.conf
System Instillation it will refer to the the Mount partition table from the /etc/fstab file
Run level it will refers to the /etc/inittab file
After Reading this question, you may intrigue about
what is MBR?
What is GPT?
How To Convert MBR to GPT?
What is vmlinuz?
what is initrd? This information I have given below.
some of the important points MBR
some of the important points MBR
MBR(Master Boot Record) is special type of boot sector at the very begining of partitioned computer mass storage devices.it hold how the
1)logical partition containing file systems are organized in the medium.
2)it also contain executable code .This MBR code is usually referred as boot loader.
MBR not present on the non-partitioned media such as floppies,superfloppies or other storage device.
MBR Consist of 512 bytes.
- 446 – Bootstrap code area
- 4 primary partition (4*16 bytes=64)
- Boot Signature(2)
- Total (446+64+2=512 bytes)
4 Primary partition(every single partition can divided upto 23 partition)
Latest is GPT(GUID Partition Table) - Requirement
- why -> Since there is limitation on MBR 4 Partition/2 TB, we are going into GPT it support upto 128 partition.
- Requirement -> UEFI(Unified Extensible Firmware interface)
- Adantage ->secure boot
How Convert MBR to GPT table.
Windows we have software, Linux we can do it directly. 3 party software also avialable.
Vmlinuz – Linux kernel x86 boot executable compressed Image
- contain linux kernel code in one of object file format supported by Linux.
- It is center core of the OS and bootable. It mean -> capable of loading OS into memory and make it usable.
- Vmlinuz – Here z represent compressed file. Vmlinux – non-compressed and non-bootable form.
Charactertis about this file
- it is like object(a.o) file how we are making using gnu compiler after running source code.
- So, we can’t read this source code, instead we can read the symbol using objdump and nm command.
To Build the Linux Kernel according to the requirement Refer the following link.
Download the kernel and build it. Using this depends on our hardware/customer requiremnet we can built the OS.
initrramfs – gzip compressed data
- initramfs used by kernel temporary root file system and kernel booted with real root file system is mounted.it also contain necessary drivers,binary,library and configuraiton file.
- initramfs-2.6.32-358.el6.x86_64.img it contains following directory
It has bin,sbin,init,lib,proc,sysroot,var,lib4,tmp,dev,etc,
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