Re: loop-mounted ISO images

[<ian_bruce@fastmail.net>]

On Thu, 5 Sep 2013 11:44:54 -0400
Joey Hess <joey@kitenet.net> wrote:

>> Is there some boot parameter that can be given to the Debian
>> installer initrd to make it understand that it's running from a
>> loop-mounted ISO image file rather than a plain block device?
>> 
>> This is a well established feature in some distributions; for
>> example, in Ubuntu, the relevant parameter is
>> "iso-scan/filename=<FILENAME>".
> 
> iso-scan is part of the Debian installer[1].
> 
> However, it is only included in the hd-media initrd. There is no
> reason to include it on the regular CD initrd, because isohybrid
> allows mounting the USB stick directly. (Not a loop-mount of an iso
> file included in some disk, which the hd-media initrd handles.)

> http://http.us.debian.org/debian/dists/wheezy/main/installer-amd64/current/images/hd-media/

I've now tested this with the debian-7.1.0-amd64-i386-netinst.iso CD
image, and the kernel and initrd referenced above.

This does not work as it does with the Ubuntu live CDs. You cannot use
the boot parameter
"iso-scan/filename=/linux/debian-7.1.0-amd64-i386-netinst.iso", and
have the installation proceed with that loop mount; it cannot find the
ISO file. Conversely, if the ISO image is in the root directory of the
same partition, the initrd DOES find it, but clearly it is not
consulting the "iso-scan/filename" boot parameter.

Looking at the source code for the iso-scan package makes it clear why
this is so: "iso-scan/filename" appears to be an output, rather than
an input, as far as that package is concerned.

So I ask again: is there any boot parameter that can be used to tell
the Debian initrd the pathname (relative to some partition root) of
the ISO image file it should loop-mount as its root filesystem and run
from?

We're trying to write a utility that will allow the installation of
multiple Linux distribution ISOs on a single USB flashdrive, so that
the user can select which one to boot from, so we kind of need to know
this. The smallest flashdrive you can buy these days is 8GB; it makes
no sense that you would need a different one for every distribution
ISO that you might want to run.

http://sourceforge.net/projects/multibootusb/


-- Ian Bruce