Unable to boot LiveCD ISO from UDF filesystem

[semreh]

Using Lubuntu 18.04.2 (#lsb_release -a -> Description: Ubuntu 18.04.2 LTS)

In order to resolve a problem with booting after 'Software Updater' updated the system, I needed to boot from a LiveCD and chroot to resolve the boot issue.

GRUB allows systems to boot from an ISO image located on an accessible filesystem, so if you have sufficient disk space, you do not need to write out to a USB flash drive.

I downloaded the Lubuntu 18.0.2 from http://cdimage.ubuntu.com/lubuntu/releases/18.04.2/release/ onto a spare partition formatted as UDF version 2.0.1 and confirmed the integrity of the download with sha256sum

On attempting to boot from the ISO directly using GRUB, the boot fails. As I don't have a serial console I can't give the exact error.

As I knew I could boot from other ISO images on a separate ext2 partition, I copied the Lubuntu 18.04.2 ISO to the ext2 partition. Attempting to boot with the ISO in this location worked, I got a LiveCD system from which I could then do the necessary chroot operations to get my system working again.

GRUB script - fails when ISO is on UDF formatted partition, succeeds when on ext2 partition

setparams 'Lubuntu 18.04.2 ISO'
insmod iso9660
insmod ext2
insmod udf
insmod part_gpt
set isofile="/lubuntu-18.04.2-desktop-amd64.iso"
loopback loop (hd1,gpt5)$isofile
linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile noprompt noeject toram --
initrd (loop)/casper/initrd

I suspect the iso has been produced without including udf filesystem drivers somewhere. I suggest supporting UDF would be helpful as many people use UDF as a cross-platform alternative to FAT as it supports larger file sizes than FAT.

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

To change the source package that this bug is filed about visit https://bugs.launchpad.net/ubuntu/+bug/1820222/+editstatus and add the package name in the text box next to the word Package.

[This is an automated message. I apologize if it reached you inappropriately; please just reply to this message indicating so.]

[Steve Langasek (vorlon)]

This is presumably because you are on a system using UEFI with SecureBoot, and therefore the loading of external grub modules fails ('insmod udf'), and we do not build udf support into the signed UEFI GRUB image.

Because the UEFI GRUB image is signed into the SecureBoot regime as trusted code, the standards for security are higher, and we would no simply enable an additional filesystem driver without some measure of security review.

[semreh (launchpad-via-forwarder)]

It is an UEFI system, but NOT SecureBoot enabled.

I understand the reasons why your might not want to do this for SecureBoot enabled systems (I might not like them, but I do understand them).

In this case, I get the capability I want by making an ext2-formatted partition on the not-easily-removable persistent storage device and putting the ISO images there. It struck me that it should be possible to use a UDF formatted partition - mainly because I sometimes have to rescue broken systems, and it is convenient to be able to write out ISO files that are larger than 2 Gigabytes on removable media that are 'cross-platform' readable and writeable.

Thank you for taking the time to comment.

[Mate Kukri (mkukri)]

Hi,

I've just tested it on the current development release, and it seems to work perfectly fine, so closing as 'Fix Released'.