Re: GRUB isn't working for bootable CD

[Thierry Laronde]

Hello,

On Wed, Oct 08, 2003 at 09:33:40AM -0400, Harmon S. Nine wrote:
> For those unfamiliar with the "el torito" method of booting from CD (I 
> don't know of any other methods :), it involves storing a hard-disk (or 
> floppy-disk) image on the CD.  On booting from the CD, this image is 
> loaded from the CD into RAM as a ramdisk, 

No : the BIOS emulates a hard disk accessed via CHS commands, but the
image is not loaded in memory. This is an emulation, allowing the 
access to the CD without peculiar driver via legacy CHS commands.

> and is temporarily made the 
> primary hard-disk of the computer.  Given this, if the ramdisk has grub 
> on its MBR and grub is properly configured, the computer should boot as 
> it would from the actual primary hard-disk.  Once the boot is complete,  
> the ramdisk is deleted and things return to normal.
> 
> The version of grub that works in this capacity is 
> grub_0.92+cvs20020923, i.e. the one from September of 2002.  All 
> subsequent versions do not work (yes, I should have reported this long 
> ago), i.e. they always give an "error 18".
> 
> Is this a bug in grub, or do I need to change how grub is installed?  If 

I had made some patches (two different versions) at the time GRUB 0.92
was released. This GRUB version which "works" is a patched version and
not a vanilla one. The problem is that an El Torito able BIOS is a LBA
able one and GRUB detects the support about LBA and try to access the
boot image on the CD via LBA commands, but, unfortunately, the emulation
is a CHS one built on an LBA accessed device : by switching to LBA, GRUB
accesses the raw CD (the iso fs) and not the boot image. Hence it fails
to access stage2.

Solution : keep using GRUB 0.92 + the patches or port the patches to
0.93.

Cheers,
-- 
Thierry Laronde (Alceste) <address@hidden>
Key fingerprint = 0FF7 E906 FBAF FE95 FD89  250D 52B1 AE95 6006 F40C