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Re: grub + GPT BIOS boot partition

From: Andrei Borzenkov
Subject: Re: grub + GPT BIOS boot partition
Date: Sat, 4 Oct 2014 22:56:37 +0400

В Sat, 4 Oct 2014 17:39:38 +0000
"Boylan, Ross" <address@hidden> пишет:

> The manual (3.4) says, for GPT and the BIOS boot partition
> "With partitioning programs that require setting the GUID directly, it should 
> be ‘21686148-6449-6e6f-744e656564454649’.
> Caution: Be very careful which partition you select! When GRUB finds a BIOS 
> Boot Partition during installation, it will automatically overwrite part of 
> it. "
> Does this mean that the installer will overwrite the BIOS Boot partition on 
> every disk that has one (since they all have the same GUID), or only on the 
> target disk?

Only on target disk.

>                                                               Giving the same 
> GUID to different partitions seems like a recipe for
  trouble.  Or is the GUID some type flag in GPT and not the partition

It is partition type.

> What happens with a GPT disk that does not have a BIOS boot partition?

grub-install will refuse to install grub2 on while disk (/dev/sda as

> I'm also a little confused about the role of the BIOS boot partition vs /boot 
> for Linux systems.  I thought the installer wrote itself into /boot.  Is it 
> that some of the key components also go in BIOS boot so that grub knows 
> enough to be able to read /boot?

Yes, this is core.img which contains enough code to be able to read
remaining of grub from /boot.

MBR traditionally had empty space before first partition which is used
to store bootloader. GPT has nothing like it, so bios_grub partition is
used to reserve space on disk to ensure it won't be allocated to
another partition.

> Thanks.
> Ross Boylan
> cc's appreciated.
> _______________________________________________
> Help-grub mailing list
> address@hidden

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