Problems with dual boot and grub
Jim Cornette
jim-cornette at insight.rr.com
Mon Mar 22 04:24:02 UTC 2004
Jeff Vian wrote:
>
>
> Jim Cornette wrote:
>
>> jludwig wrote:
>>
>>> How does toe BIOS know to go to that partition???
>>>
>>>
>>>
>> The bios will get information from the partition table. For example,
>> you can set the active partition on hda1,hda2 or hda3 on my setup.
>> They are primary partitions. The active partition is marked with an *
>> for the active partition using fdisk (linux version).
>>
>> You can't boot from hda4 (extended container) or from hda5 (partition
>> in an extended partition, BIOS is not smart enough to do this.) So
>> you should be able to boot from any partition that you install grub
>> in, as long as it is a primary partition.
>>
>> Why I have an extended partition that is all used up by linux swap is
>> a bit worthless, but that is the way the installer set it up.
>>
> You cannot have more than 4 partitions on a drive. When the 4th
> partition is created it makes it an extended and then creates the
> logical partition inside, thus hda5
>
>> You can set the active partition using the fdisk for windows also. I
>> believe it uses "A" to denote which is the active partition.
>>
>> Jim
>>
>> Device Boot Start End Blocks Id System
>> /dev/hda1 * 1 2173 17454591 7 HPFS/NTFS
>> /dev/hda2 2174 2186 104422+ 83 Linux
>> /dev/hda3 2187 3583 11221402+ 83 Linux
>> /dev/hda4 3584 3648 522112+ f Win95 Ext'd (LBA)
>> /dev/hda5 3584 3648 522081 82 Linux swap
>>
>>
> AFAIK you can only have one "active" partition on a drive, thus only
> one to boot from.
The BIOS goes to the mbr first and if it is not redirected by the mbr
content, it goes to the only active partition that you mentioned.
On this setup, grub is installed in the mbr. If the mbr was overwritten,
it would boot into the partition marked active (XP in example)
If I installed grub to /dev/hda2 and then made the partition active,
grub will boot and be able to redirect the boot according to the
grub.conf file. I could boot into grub without it being installed in the
mbr.
If you have an installation that is located in an extended partition,
you couldn't boot into it without grub being installed in the mbr. This
is from my experience. On another system that I have, I use the mbr to
boot an installation that is installed on the extended
partition(http/ftp installed fedora core development). I then chainload
two other installations that I have grub installed in hda1 (boot for
Fedora Core1) and hdb2 (boot for fedora core 2 test) respectively. I
haven't found a self supporting way to boot grub on an extended
partition any other way than on mbr though. Sorry for repeating.
So you are right about only one active partition.
Jim
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