[Mageia-dev] Grub2 vs. Grub Legacy in M3

[Barry Jackson]

On 21/01/13 00:01, Frank Griffin wrote:
> On 01/20/2013 02:58 PM, Maurice Batey wrote:
>> On Sun, 20 Jan 2013 20:04:32 +0200, Thomas Backlund wrote:
>>
>>> http://svnweb.mageia.org/packages/cauldron/grub2/current/SOURCES/README.Mageia?view=markup
>>>
>>    Many thanks, Thomas!
>>
> Look, I don't don't want to restate the obvious, but you *do* realize
> that in order for chainloader to work, you actually have to install the
> secondary bootloader on the PBR of its owing partition ?  You can't just
> have installed grub on your MBR at some point in the past, then install
> grub2 (or anything else, for that matter) on the MBR again, and expect
> your original partitions to boot ?
>
> In MGA install terms, and specific to the case of grub2 on the MBR
> trying to boot grub on a PBR, you have to boot the grub partition (or do
> the boot-elsewhere/chroot thing), modify the /boot/grub/install.sh to
> not target the MBR (stage2=(hd0)) but indicate the PBR (stage2=(hd0,x))
> and rerun install.sh to install grub on the PBR.
Err...

# grub
root (hdx,y)
setup (hdx,y)
quit

Job done - there is no need to touch install.sh

>
> In terms of the install paradigm, you have to choose to install the
> bootloader to the PBR (sdaX) rather than the MBR (sda).  Otherwise, when
> the MBR bootloader, whether grub2 or grub, boots and chains to the PBR
> of the desired partition, there won't be anything there in the PBR to boot.
>
True, except as below...

> If you need clarification on this, ask, and give specifics.  The
> objective of chainloading is to have each PBR (partition) behave as if
> it is its own MBR.  If you try to point grub2 menu entries to native
> partiton grub files, or vice versa, you are just asking for trouble. The
> clean way to do it is to use chainloading to link the MBR (whatever it
> is) to the PBR (whatever it is), and let the PBR do the bootloading for
> its own partition according to its own needs.

...this is where we disagree slightly ;)
Chainloading into grub2 is not the best way, due to the block lists 
problem people keep mentioning and complaining about.
Grub2 can install it's kernel in the root filesystem which can be booted 
directly. Installing the grub2 package, whether during install or later 
automatically builds /boot/grub/i386-pc/core.img and also creates a 
grub.cfg ready for use.
Chanloading is un-necessary since an entry in menu.lst on a legacy 
system will boot a grub2 Mageia system using:

  	title Mageia via GRUB 2
	root (hdx,y)
  	kernel /boot/grub2/i386-pc/core.img

...as explained in the above README.Mageia
>
> If you do it this way, you can install whatever you want as a bootloader
> on the MBR, and each partition can have whatever BIOS-compliant
> bootloader it wants, including grub, grub2, lilo, OS/2, DOS, or Wndows.
>
Yes, I use a small grub2 partition sda1 as "master".
To boot into Mageia grub2 systems I use the grub2 multiboot command:

	menuentry 'Mageia-3 multi sda6' {
	search --no-floppy --label --set=root mageia-3
	multiboot /boot/grub2/i386-pc/core.img
	}

So IMO all of the FUD about "you can't install grub2 to the PBR" is 
pointless since it's just not necessary.

My 2 cents ;)