Re: Beware using modules from different grub versions (was error: cannot allocate real mode pages)

[Glenn Washburn]

On Tue, 10 Sep 2013 06:59:18 +0400
Andrey Borzenkov <address@hidden> wrote:

> > Regardless, there's another issue, the difficulty in ensuring where
> > modules are being loaded from.  Currently, modules are searched for
> > in the $prefix directory.  But $prefix is used for many other
> > things as well, like config loading and font loading.  So if you
> > want the fonts coming from the ubuntu install, but the modules
> > coming from a newer grub, you have problems.
> >   
> 
> grub is using whatever font is loaded using loadfont command. So just
> load it from your preferred location.

This may not be known until runtime or may not be desirable to
hard-code it into the config.  If you want to load a particular OS's
grub install, you might like to load its interface as if you had booted
from that grub install directly.  So let it load whatever font it
wants.  You shouldn't need to care about it.  This generally works now
by making sure the $prefix is correctly set before a "configfile"
command.

> > I see two potential, non-mutually exclusive solutions.   
> 
> I'm afraid I miss the problem.

The problem, as stated above, is that $prefix is used as a base
location for many types of grub files (fonts, modules, configs,
locales, etc..).  It may not be desirable to load all these from the
same prefix.  As I found out after banging my head against a wall for a
couple of days trying to figure out why grub was failing to load my
ubuntu install with the "error: cannot allocate real mode pages".  I
don't want the grub modules to load from the older ubuntu grub install,
however I do want $prefix to point to the ubuntu grub install location
so that locales, fonts, configs, etc.. are properly located.

I'm using multi-purpose USB stick (boot several different machines and
isos), which is installed with the repo HEAD to boot my ubuntu server
which has a non-bootable (inside an encrypted container) ubuntu
install, which has an older version of grub installed.

Does that help to clarify?