The bootmenu for zfs based Ubuntu does partly not work

[BertN45]

I had a triple boot since April:
- Ubuntu 19.04 on ext4
- Ubuntu Mate 19.04 on zfs
- Xubuntu 19.04 on zfs

Each zfs based system is stored completely in its own dataset, all folders are in that dataset; var; usr; home and all others.
I have upgraded all systems to 19.10 and it went reasonably well, but I produced a few bug reports for some minor errors or typical transition problems. I did reinstall Ubuntu 19.10 on ext4 to solve one of those transition issues.

All systems work fine now and I can boot all from Linux 5.2.

Since the Software-Updater does not work anymore, I had to do the updates using apt in the terminal, but I created two snapshots for both zfs systems one 190908 and one 190911.
After running update-grub and grub-install those snapshots appear in the boot menu, hurrah!

However except the main Linux 5.2 one for each OS, none of the menu entries is working:
- The memory test ends up with a blank screen and nothing seems to happen. That entry has been added by the main zfs based system;
- The history entries tell me "wrong dnode type" and "the correct kernel must be loaded first" and then it returns to the boot menu;
- The advanced entries
Both Linux 5.2 and 5.0 recovery modes stop after loading the RAM disk. The system hangs, but the disk light blinks each 5 seconds.

Linux 5.0 normal mode says: it will not load due an incompatibility with the datapool. That happens because I decided to upgrade the datapool itself.
In the release notes you need a strong warning about the consequences of updating the datapool!! Also during upgrading dual or multi boot systems. I did run into problems with it; even when I initially only updated the pool with the data and left the pool with systems and VMs unchanged.
The last pool (systems and VMs) has been updated, when I completed the upgrade of the systems.

[BertN45 (lammert-nijhof)]

I have removed Linux 5.0 everywhere, since it was using ZFS 0.7.12 and I also removed the snapshots containing Linux 5.0. I now only have 5.2 and 5.3 in the system with one new snapshot, but all problems remain the same.

[Sebastien Bacher (seb128)]

thank you for the bug report, what do you expect from gdm though?

[BertN45 (lammert-nijhof)]

What I expected is that those menu entries would work as said in that menu line.

However the situation completely changed, because the Grub menu has been "rolled back" by an update to a more classic view without the history menu entry and only one classic recovery mode per Linux version in the advanced menu options.
Booting from ZFS:
The Recovery Mode in the Advanced Options still hangs after loading the ramdisk.
Booting from ext4:
The Recovery Mode in the Advanced Options hangs with a blank screen.

The Memory Test does not start, after one beep the screen blanks and the system is dead.

All other menu entries work as expected, so I can load Ubuntu with linux 5.2 or 5.3 versions.

I liked the History menu Entry, so you could boot the system once or definitively from a snapshot. That was nice to have, but not essential, since on another PC I rolled back manually from 19.10 to 19.04 after I detected that Virtualbox 6.0.12 did not support Linux 5.3 yet.

[Didier Roche-Tolomelli (didrocks)]

Only zsys systems will have rollback, we had to revert rollback in pure ZFS systems as per this package upload: https://launchpad.net/ubuntu/+source/grub2/2.04-1ubuntu7.

Indeed, we need to release note that people shouldn't upgrade the bpool as grub isn't able to read newer zfs pool versions.

[Sebastien Bacher (seb128)]

the issue there doesn't have anything to do with the desktop login screen though and there seems to be no real/concrete bug, best to use discourse for discussions and suggestions, closing this ticket