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Re: lilo removal in squeeze (or, "please test grub2")

On Wednesday 26 May 2010 13:23:44 Stefan Monnier wrote:
> > for much.  But I am opposed to the removal of lilo.  Both grub-legacy and
> > grub-pc use sectors on the hard disk outside of the master boot record
> > (cylinder 0, head 0, sector 1).  In other words they use cylinder 0, head
> > 0, sector 2 and possibly subsequent sectors on cylinder 0 head 0.
> Really?  Never heard of it, and it sounds very odd: why would they do
> that when they can (and do, AFAICT) use sectors on specified partitions?
> Is that documented/discussed somewhere?

That's where the stage 1.5 is embedded, AFAIK.  Using sectors allocated to a 
partition would be extra bad -- not everything that "consumes" a block device 
avoids using the first so many bytes.  (XFS for one.)

If you know that the first part of a partition is not used by the file system 
on it (or LVM, or RAID, or whatever that consumes that block device), GRUB 1 
does support embedding the stage 1.5 in a partition.

GRUB's stage 1 is an MBR, and resides where it should.  GRUB's stage 1.5 is 
the code that understands the file system, and resides between the MBR and the 
first partition.  GRUB's Stage 2 does the menus, kernel/initrd loading, etc.  
It resides as a file on a file system.  That's my understanding how how GRUB 1 

GRUB 2 is a different beast in some respects, but my understanding is that 
these stages still apply, conditionally.  Depending on the modules needed, the 
stage 1 may be able to load modules from the file system and boot directly.  
Failing that, a stage 1.5 is still used.  When using a "DOS" partition table, 
it is embedded between the table and the first partition; When using a GPT 
partition table, it is embedded in a dedicated partition--GPT uses the space 
between the table and the first partition.  The stage 1.5 is used to load 
modules from the file system.  In GRUB 2, there is no single "stage 2"; 
whatever modules are loaded from the file system fill that role.  I don't know 
if GRUB 2 still supports embedding the "stage 1.5" at the beginning of a 
partition under a "DOS" partition table.
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