[Grml] grub2 loopback feature

Alexander 'Leo' Bergolth leo at strike.wu.ac.at
Thu Jun 17 21:46:28 CEST 2010

On 06/17/2010 07:22 PM, Michael Prokop wrote:
> * T o n g <mlist4suntong at yahoo.com> [Thu Jun 17, 2010 at 05:14:40PM +0000]:
>> On Tue, 15 Jun 2010 17:38:59 +0200, Alexander 'Leo' Bergolth wrote:
>>> I'd like to use the loopback feature of grub2 to boot a grml iso-image
>>> that resides on a USB drive.
>> IIRC, mika wrote about it in his blog, http://grml.supersized.org/
>> Hmm..., no, maybe somewhere else, 'cause searching loopback didn't help.
> I wrote:
>   http://michael-prokop.at/blog/2009/05/25/boot-an-iso-via-grub2/
> And for the german speaking people, Marc Haber wrote about it as
> well:
>   http://blog.zugschlus.de/archives/825-grml-als-eigenes-Rescuesystem.html

I know about those articles but my question was another one:

> Is there a way to make grub jump to the existing /boot/grub/grub.cfg in
> the ISO and show its contents as a submenu?

I am trying to branch to grmls own grub configuration:
-------------------- 8< --------------------
  loopback loop $iso_path
  set root=(loop)
  configfile /boot/grub/grub.cfg
-------------------- 8< --------------------

... which seems to fail because of a bug in grub. (set root=(loop) fails)
See http://savannah.gnu.org/bugs/?30143 for the bug report.

As a workaround, I suggested to prepend a variable like ${loop} to all
paths in grmls grub.conf, which could be set to loop="(loop)" by the
calling grub.cfg on the usb drive. Besides a variable like ${kernelopts}
at the end of each kernel commandline would allow passing custom boot
options from the calling grub.cfg.

e-mail   ::: Leo.Bergolth (at) wu.ac.at
fax      ::: +43-1-31336-906050
location ::: IT-Services | Vienna University of Economics | Austria

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