Re: [gentoo-user] setting boot flag on sda1

[Todd Goodman <tsg@bonedaddy.net>]

* Joseph <syscon780@gmail.com> [140905 13:37]:
> On 09/05/14 13:12, Todd Goodman wrote:
> >* Joseph <syscon780@gmail.com> [140905 12:14]:
> >> How to set a boot flag on sda1.
> >> I'm using fdisk from util-linux 2.24.1 and in order to set it I need version  2.22 or earlier
> >>
> >> --
> >> Joseph
> >
> >If you're using GPT partitions then you should really be using gdisk or
> >recent parted (gparted.)
> >
> >You'll see strange results if you use fdisk to look at GPT partitions (for
> >some definition of strange and depending upon if a hybrid configuration
> >is used.)
> >
> >Todd
> 
> Yes, it make more sense. 
> 
> Will old BIOS boot GTP partition disk.  
> My system does not recognize boot sector.  It thinks there is no disk.  
> I can boot current disk with Systemrescue CD but BIOS does not see my boot sector or the way it is installed.	
> 
> 
> -- 
> Joseph

What does 'gdisk -l /dev/sda' say about GPT and MBR (it usually says
whether you have a valid GPT and/or MBR before printing information
about the partitions.)

As others have mentioned, you need that BIOS boot partition for GRUB2 to
embed its core.img into since there's no post-MBR gap for it to use with
GPT.  This is different than the partition you mount as /boot.

Your BIOS should be able to boot GPT drives but it can be flaky
depending upon motherboard in my experience.

If using GPT drives to boot with BIOS you want a protective MBR which
encompasses the entire drive (or first 2.2TB if the drive is larger than
that as that's as big as MBR can handle.)  It has type 0xee.

You can create that gdisk (by going into the eXpert menu) or you can use
fdisk to create it.

With some motherboards you have to flag the protective MBR as bootable.
You can do this in fdisk with the 'a' command or in gdisk with the 'a'
command on the eXpert menu.

grub2 should have installed the correct target by default (i386-pc) but
you can force that with the --target command line option to
grub2-install ('grub2-install --target=i386-pc /dev/sda' for example)

So barring a really strange BIOS implementation you should be able to
boot a GPT partitioned drive on a BIOS-based computer but I have to ask
why you want to go through all the head-banging?

Since your BIOS isn't cooperating the only reason I could see is if your
drive is larger than 2.2TB (quite possible but I don't remember from
earlier in the thread.)

Todd