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There seems to be problems loop mounting ISO files with grub 2.04, how to downgrade to grub 2.02?

Grub 2.02 works for loop mounting ISO files on a Bootable pendrive.

I think the main problem comes when booting in UEFI mode.

Reference: Grub command loopback loop… does not work on Ubuntu 19.10 Grub command `loopback loop...` does not work on Ubuntu 19.10

Further Reference: LaunchPad https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1851311

C.S.Cameron
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    Please describe the real problem. The question looks like an [XY problem](https://meta.stackexchange.com/q/66377/295481) – Pilot6 Nov 07 '19 at 10:44
  • One simple way is to install an older version of Ubuntu for example 18.04.1 LTS alongside the other operating system(s). Then run `sudo update-grub` to get access to the other operating system(s). It costs a few GB, so there might be better methods. – sudodus Nov 07 '19 at 13:20
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    @sudodus: Ah Ha! So for an ISO booter, I use mkusb to make the foundation using say 18.04 and then it should have no problem booting 19.10 and newer ISOs. Very clever. Please drop this solution into an official answer. – C.S.Cameron Nov 08 '19 at 02:56
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    All my flash drives have grub and most are still grub 2.02. Some have full installs and only one or two may be 2.04, and some just have grub for loopmounting a variety of repair ISOs. I only use 25GB for / (root), so still have 14.04,16. 04 & 18.04 on my boot SSD. I am planning on overwriting 14.04 with 20.04, but already have 20.04 on HDD to test. Microcenter store is just a couple of miles away. (not a plug for Microcenter, but flash drives are inexpensive & for me have worked well). The real problem is price is lower or capacity higher so I keep buying more. I try not to go too often. :) – oldfred Dec 15 '19 at 16:55
  • @oldfred: Yes they are not only getting cheaper and larger, they are not lasting near as long. Some of these super multi-layer drives are only good for a few hundred writes and not 10000+ writes like the old flash drives. – C.S.Cameron Dec 16 '19 at 03:24

2 Answers2

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I started by suggesting:

One simple way to get grub 2.02 is to install an older version of Ubuntu for example 18.04.1 LTS alongside the other operating system(s). Then run sudo update-grub to get access to the other operating system(s). It costs a few GB, so there might be better methods.

You brought this idea one step further:

Ah Ha! So for an ISO booter, I use mkusb to make the foundation using say 18.04 and then it should have no problem booting 19.10 and newer ISOs. Very clever. Please drop this solution into an official answer.

And you have a solution :-) or should we say a workaround until the bug in grub 2.04 is squashed :-/

sudodus
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Workaround for Booting ISO's with GRUB 2.04

I put rmmod tpm on it's own line in grub.cfg, up top, just above the fi line allows booting ISO's in UEFI mode

Booting the USB in BIOS mode, grub 2.04, works okay.

Booting the USB in UEFI mode, grub 2.04, also works okay. Both modes boot with no no such module error messages.

Both modes proceed to Disk Check unless fsck.mode=skip is added to the GRUB menu entry.

Neither mode goes to the Try/Install screen when booting, nor ask to remove drive and press enter when quitting.

C.S.Cameron
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