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Re: Grub cannot fit into boot record



On Sun, Jan 15, 2012 at 2:35 PM, Stephen Powell <zlinuxman@wowway.com> wrote:
> On Sun, 15 Jan 2012 08:24:40 -0500 (EST), Arno Schuring wrote:
>> John Hasler (jhasler@newsguy.com on 2012-01-14 12:25 -0600):
>>>
>>> IMHO putting critical
>>> boot software in an "unallocated" area that other software will (not
>>> unreasonably) assume contains nothing important is a loony idea.
>>
>> It's not any more loony than hardcoding the disk sectors in which the
>> kernel file resides.
>
> The stage 1 boot loaders of both grub-pc and lilo hard code the
> location of the next stage. But for lilo, this is in a file in
> the Linux file system (by default it's called /boot/map). For
> grub, for a disk in the MS-DOS format, it is usually stored in
> unallocated sectors between the master boot record and the first
> partition. The key word is "unallocated". Backup programs may
> not back them up. Restore programs may not restore them.
> And other programs, assuming that the unallocated sectors are
> empty, may decide that they want to store stuff there too,
> causing a conflict. And if there are no unallocated sectors
> between the master boot record and the first partition, grub
> cannot be installed (at least not in the preferred way).
> In my humble opinion it is best to avoid the use of unallocated
> sectors altogether, if possible, for the reasons listed above.
>
> When used with disks in the GPT format, I believe that grub
> uses a separate boot partition, rather than unallocated sectors.
> But I'm not a grub expert; so I'm not sure about that.  lilo
> does not support boot disks in the GPT format at this time.

AFAIK, using the post-MBR gap _can_ be a problem but only if you're
dual-booting with Windows because some Windows software publishers use
it too.

When using a gpt-labeled disk, grub2's MBR stage ("boot.img") points
to a stage ("core.img") stored in the disk's first partition (usually
1MB) that d-i and anaconda's partitioners call a "bios boot partition"
and parted calls a "bios grub partition."


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