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Just curious... I am installing Debian Squeeze, right now. Do I really need to install grub (or any boot loader) since I am only installing one OS. Seems like I ...
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  1. #1
    Linux Enthusiast flipjargendy's Avatar
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    Question Do I really need to grub it up?!


    Just curious... I am installing Debian Squeeze, right now. Do I really need to install grub (or any boot loader) since I am only installing one OS.

    Seems like I shouldn't have to. BIOS takes care of that if there is one OS... right?
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    BIOS takes care of that if there is one OS... right?
    Wrong. The bios will only read the boot code in the MBR of the HDD. When you install grub, its boot code is written to the MBR so the bios can read it and then hand over control to it. With no boot code in the MBR the computer will not boot.

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    Linux Enthusiast flipjargendy's Avatar
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    So I will need Grub or Lilo installed for sure?

    It seems like the BIOS should just say "boot this partition/HD" and be done, all on its own. No?
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    So I will need Grub or Lilo installed for sure?
    Yes for sure . If you have more then one linux installed, only one Grub /Lilo needs to be installed.

    With all the different OS's that could be installed on the hdd along with the number of hdd's in system it would be very difficault to write the bios code for all possibilties. The standard was decieded that the very first sector of hdd (MBR) would be read by the bios and control would be turned over to it, if code was present. If no boot code is found the bios may try a different hdd, floppy or cd. If no boot code is found on any device the bios will give an error -no system disk- or simular wording.

  5. #5
    Penguin of trust elija's Avatar
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    Quote Originally Posted by flipjargendy View Post
    So I will need Grub or Lilo installed for sure?

    It seems like the BIOS should just say "boot this partition/HD" and be done, all on its own. No?

    You definitely need a bootloader. Otherwise it's kind of like stopping and asking for directions and being told but you should already know where that is. But without the random chance of finding it on your own.
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    Linux Newbie theNbomr's Avatar
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    The role of the BIOS is to find a bootable primary partition with a legitimate Master Boot Record, then load and execute the first sector (MBR) of that partition. In theory, one could contrive a kernel that self boots by loading the rest of itself after having its first 446 bytes launched by the BIOS. In practice, this is what bootloaders do best, so most people prefer to use them.
    The notion of embedding knowledge of partition schemes and filesystem types into the BIOS is not a model that supports general purpose use of the system, and tends to stagnate evolution of new standards. The BIOS is essentially an immutable fixture in the system, and for greatest flexibility, should not rely on any but the most basic standards. That there will always be a 'sector 0' is about as general and simple as you can get.
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    Linux Enthusiast Bemk's Avatar
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    I thought the Linux kernel used to support self booting once, but they've removed that option several years ago (yes, I have looked into the history of the system I am using, computer history can be a lot of fun).

    You could theoretically put the self booting code back in, recompile the kernel and see what it does. I recommend you just go with GRUB or LILO though as it will save you lots of headaches. If you really want to get rid of the boot loader, I think BSD doesn't require it. As long as the kernel is installed to the MBR. I'm not sure though.

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    Linux Engineer Segfault's Avatar
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    Quote Originally Posted by Bemk View Post
    I thought the Linux kernel used to support self booting once, but they've removed that option several years ago (yes, I have looked into the history of the system I am using, computer history can be a lot of fun).
    True, when I started using Linux back in 1997 Linux kernel was bootable by BIOS directly.

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    Linux Enthusiast Bemk's Avatar
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    I know this is a bit off topic, but I'm going to ask it anyway:

    Could you please tell me the state of the machine that a kernel has to expect, when loaded by grub?

    It's just a bit of curiosity.

  10. #10
    Linux Newbie theNbomr's Avatar
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    Could you please tell me the state of the machine that a kernel has to expect, when loaded by grub?
    The answer to this is quite architecture-specific. For PC-type architectures, Inside the Linux boot process gives a pretty good explanation of the state of affairs and the process that takes place as a kernel is launched by a bootloader.
    --- rod.
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