Ubuntu CD Images

(x)Ubuntu ISO - loopback.cfg file is missing

Bug #1900185 reported by Adrian Feliks
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Ubuntu CD Images
Fix Released
Undecided
Unassigned

Bug Description

Starting with Ubuntu 20.10, the file /boot/grub/loopback.cfg is not available on the ISO images (https://releases.ubuntu.com/20.10/ubuntu-20.10-beta-desktop-amd64.iso).

Grub2 allow to run operating systems directly from ISO files.
Due to the fact that the above file is not available, it does not allow the menu to be loaded automatically when Ubuntu starts from the ISO image.
I suggest restoring this file, or adding the following entry in the /boot/grub/grub.cfg file to each menu: "iso-scan/filename=$iso_path"

Adrian Feliks (mexit)
summary: - xUbuntu ISO - loopback.cfg file is missing
+ (x)Ubuntu ISO - loopback.cfg file is missing
Revision history for this message
Steve Langasek (vorlon) wrote :

This appears to have been lost as part of a refactor of the debian-cd branch. Looking at the branch history, this file was added in order to support something called Super GRUB Disk, which I've not heard of or used before. Is this why you're looking for loopback.cfg to be readded?

This seems to be a very narrow use case (why write an ISO as a file on the disk, instead of writing the ISO to the disk?), but also easy for us to fix.

Revision history for this message
Adrian Feliks (mexit) wrote :

I do not care about the loopback.cfg file itself, but about this particular kernel parameter: "iso-scan/filename=$iso_path".

It can also be added in the grub.cfg file (see Manjaro Linux):

if [ -n "${iso_path}" ]; then
  isoboot="iso-scan/filename=$iso_path"
fi

menuentry "Ubuntu" {
 set gfxpayload=keep
 linux /casper/vmlinuz file=/cdrom/preseed/ubuntu.seed maybe-ubiquity $isoboot quiet splash ---
 initrd /casper/initrd
}

This allows you to save many different distributions and system versions on one USB stick and makes it easy to update them later.

Example: writing an ISO image on 16 GB and bigger USB does not make sense, it is not practical.

Additionally, we can enable exfat support in the kernel, which makes it much easier to use larger ISO files (over 4 GB).

Practical examples of using "isoboot": https://github.com/Mexit/MultiOS-USB

Revision history for this message
Iain Lane (laney) wrote :

It looks like this was fixed in

  https://bazaar.launchpad.net/~ubuntu-cdimage/debian-cd/ubuntu/revision/2093

and I checked (from a groovy host, not MultiOS-USB though) that it works for me.

Please reopen if it's not.

Changed in ubuntu-cdimage:
status: New → Fix Released
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