What Does Happen During Boot Process? - BIOS and MBR


 
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Old 12-11-2009
What Does Happen During Boot Process? - BIOS and MBR

I'm talking about boot process in multi-boot Linux perceptive.

Please tell me whether my explanation is right or wrong? If wrong, please explain.

"The BIOS checks the system and loads this initial bootstrapping code into
memory. This initial bootstrap code searches for an active partition and looks for a first sector of that active partition.

After that, bootstrap code gets whatever boot code (usually GRUB Stage 1) in the VBR and loads it in memory, so GRUB Stage 1 in this case overrides the MBR initial bootstrap that's in memory.

Once GRUB Stage 1 is in memory, it takes GRUB Stage 2 from /boot/ and loads it memory. Thus, GRUB Stage 2 overrides the GRUB Stage 1.

Now once GRUB Stage 2 is in memory, it presents an interface where the user
can select which OS to boot.

Once OS is selected, the GRUB stage 2 loads the selected Kernel into Memory, so the chosen OS Kernel overrides GRUB Stage 2.

Now this Kernel has the control and finishes the process.
"

Thanks!
 
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BOOT.CONFIG(5)						      BSD File Formats Manual						    BOOT.CONFIG(5)

NAME
boot.config -- Configuration file for the boot blocks DESCRIPTION
The boot.config file contains options for the FreeBSD boot block code. When the FreeBSD boot loader runs, it searches the ``a'' slice of the boot partition for a boot.config file (as a result, slices which are missing an ``a'' partition require user intervention during the boot process). If the boot.config file is found, its contents are used as the default configuration options for the boot block code and are echoed to the system console. A valid format of this file is to put BIOS drive number, a controller type, a unit number, a partition, a kernel file name, and any other valid boot(8) option on a single line, as it is done at the ``boot:'' prompt. The options related to the boot image selection described below and all the other options available for boot.config are documented in detail in the boot(8) manual page. FILES
/boot.config parameters for the boot blocks (optional) EXAMPLES
The command: # echo "-P" > /boot.config will activate the serial console of FreeBSD. The command: # echo "1:ad(1,a)/boot/loader" > /boot.config will instruct the second stage of boot(8) on the first disk to boot with the third boot(8) stage from the second disk. The command: # echo "1:ad(1,a)/boot/loader -P" > /boot.config will do both of the above. SEE ALSO
boot(8), loader(8) AUTHORS
This manual page was written by Daniel Gerzo <danger@FreeBSD.org>. BSD
May 13, 2007 BSD