Dracut fatal don't know how to handle root=zfs:rpool/ROOT/ubuntu

[Sithuk]

I upgraded an Ubuntu system recently to the next distro version and was unable to boot. I could get into zfsbootmenu ok. When I tried to boot the boot environment I got the following error.
Dracut fatal don't know how to handle root=zfs:rpool/ROOT/ubuntu

I realise there have been a few breaking changes this year with a new version of ZFS and also breaking changes in zfsbootmenu so possibly I've just experienced those. I can just revert the VM to go back to before I upgraded. I was wondering if there was a way to fix the issue from chrooting into the system from zfsbootmenu? There may be some users who can't so easily revert to a previous VM state.

I tried unsuccessfully setting a zfsbootmenu root prefix property on the pool and also editing the kernel command line in the refind config. The esp wasn’t available to mount at /boot/efi either. So I couldn’t update zfsbootmenu.

[Sithuk]

False alarm.

I simply forgot to update my initramfs before I rebooted (sudo update-initramfs -c -k all). [Thank you Zdykstra for pointing me in the right direction to solve the problem.]

I also forgot that /boot/efi wasn't automounted in zfsbootmenu chroot. I only had to "mount /boot/efi" to mount it.