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  1. #1

    Question in Booting Sequence?

    Hello friends,
    I am a new member to this group and new to Linux also...
    Just starting to digest the concepts and i got stuck .......The Problem ...............BOOT SEQUENCE!!!!!!!!

    Let me first tell you in short what i understood.. so that u may point out if there's anything wrong in it.

    First the computer initiates post and after that the bios passes control to the very first sector of the hard disk. This area on the hard disk also known as the MBR contains the IPL(Initial Program Loader). Passing control to the IPL by the BIOS is the first Stage. The IPL then loads the grub.conf file to the memory. This grub.conf file resides in /boot/grub/grub.conf .

    QUESTION 1: If the IPL cannot understand the filesystem how can it understand /boot.....? It shouldn't unless the filesystem is loaded.

    Then the grub.conf file loads in memory.
    Then grub decides the location of a splash image(hd0,0-which means first partition in first harddrive) and loads it along with the menu
    . The Menu helps us to choose the OS or Kernel or whatever. Here again there is a line of code ---- root(hd0,0).

    QUESTION 2: What is the use of the line root(hd0,0)?

    I couldn't understand what happens after that. I just know that the kernel and the initrd loads into memory and the init process takes over. I understood what happens after init process takes over.

    So Can anyone please explain the process which takes place after the line stating root and before initrd?????

  2. #2
    Linux Engineer Freston's Avatar
    Join Date
    Mar 2007
    The Netherlands
    Welcome to the forums!

    Is this and this what you are looking for?
    Can't tell an OS by it's GUI

  3. #3
    Linux User
    Join Date
    Dec 2007
    Idaho USA
    along with info from sites in Freston's post:

    Question #1:
    Details of GRUB on the PC
    It shows a basic hex code of grub installed in the MBR.
    At offset 44 to 47 is the embedded physical sector address for Stage2, in his case it is b8 85 64 00 in little endian format or 006485b8 hex. Grub at this point does not know how to read any file system.

    As far as I can understand if one would move the partition ,therefore stage2 file, grub would need reloaded.

    offset :
    40=Boot Drive- ff-get from bios : 80- 1st hdd : 81- 2nd hdd --ect.
    some computers need it set to Number not to ff (ff is normally what is used)
    {would need to run Grub install with the d switch.}

    41=use LBA addressing
    42 & 43 =Start address of state 2 (?)

    Question #2:
    It tells grub stage 2 to mount the specified partition so file system can be read.

  4. $spacer_open
  5. #4
    Thanks for ur answers friends. i have one more doubt

    the grub.conf file in my redhat distribution has some lines which are as follows

    root (hd0,0)
    kernel /vmlinuz-version ro root=/dev/sda2
    initrd /initrd-version.img

    I understood that root(hd0,0) means that the it is an indication that the kernel is in the first partition of the first harddrive. but what is the use of the
    root=/dev/sda2 in the same line

  6. #5
    Linux User
    Join Date
    Dec 2007
    Idaho USA
    Looks like you have different Boot and Root partition. I think the /Boot (hd0,0) partition will contain only the Grub boot files , while the /Root partition (/dev/hda2) contain the linux kernel files.

    Go to Grub From the Ground Up and read after the first NOTE:

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