The Ubuntu 20.04 installer supports a ZFS root filesystem, which works well until an install or update involves touching the grub configuration.
I have tracked down what looks like the root cause in /etc/grub.d/10_linux
What is the best way to contact one of the developers that works on grub?
I did some Google searches but failed to find anything for this problem. After installing 20.04 using the ZFS root option I installed Xen. When it rebooted it failed in initramfs with the error "No pool imported". I was able to boot the previous kernel. When I examined the /boot/grub/grub.cfg I found what looked like invalid "root=ZFS=" options like this:
"root=ZFS=/ROOT/ubuntu_xxxxxx"
The previous kernel that boots looks like this:
"root=ZFS=rpool/ROOT/ubuntu_xxxxxx"
After looking in /etc/default/grub and /etc/grub.d I was unable to figure out why they were different and how I could change it.
As a test saved a copy and edited /boot/grub/grub.cfg adding the rpool to each "root=ZFS=" line where rpool was missing. This time I was able to boot the Xen kernel.
Questions:
How do I fix the grub configuration with "root=ZFS=rpool/" so the normal tools like grub2-mkconfig/update-grub will work?
Is this a bug in 20.04, or did I do something wrong like the order I installed packages?