No bootmenu items generated by grub-mkconfig on ZFS

[Vladimir S.]

Environment:
# lsb_release -rd
Description: Ubuntu 22.04.3 LTS
Release: 22.04
# apt-cache policy grub2-common
grub2-common:
  Installed: 2.06-2ubuntu7.2
  Candidate: 2.06-2ubuntu7.2
  Version table:
 *** 2.06-2ubuntu7.2 500
        500 http://cz.archive.ubuntu.com/ubuntu jammy-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     2.06-2ubuntu7 500
        500 http://cz.archive.ubuntu.com/ubuntu jammy/main amd64 Packages

Observed behavior: Got unbootable system after kernel upgrade.

Expected behavior: Booting perfectly booting shiny new linux system. :-)

Symptoms:
Ubuntu 20.04 is installed on ZFS. Datasets on bpool (and rpool) use are being snapshot as part of recovery plan. Package upgrade triggered grub-mkconfig. There is always a lot of warnings. This time the generated grub.cfg contained no items to boot linux. The system was unbootable.

Steps to reproduce (and correction):

Run
# grub-mkconfig

observe stderr message "/etc/grub.d/10_linux_zfs: 905: GRUB_DISTRIBUTOR: parameter not set"

and the output from /etc/grub.d/10_linux_zfs is empty in stdout.

Run
# GRUB_DISTRIBUTOR= GRUB_CMDLINE_LINUX_DEFAULT= GRUB_CMDLINE_LINUX= grub-mkconfig

the output contans linux boot items generated by /etc/grub.d/10_linux_zfs

Comments and suggestions:
It seems that either the required parameters (environnment variables) are not set during apt-upgrade or 10_linux_zfs misbehaves when optional parameters in envvars are missing.
I can't decide.
Anyway, there is an availability problem after upgrade, so I am considering this as a security incident.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: grub2-common 2.06-2ubuntu7.2
ProcVersionSignature: Ubuntu 6.5.0-17.17~22.04.1-generic 6.5.8
Uname: Linux 6.5.0-17-generic x86_64
NonfreeKernelModules: zfs
ApportVersion: 2.20.11-0ubuntu82.5
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Sun Feb 11 08:07:09 2024
InstallationDate: Installed on 2022-11-19 (448 days ago)
InstallationMedia: Ubuntu 22.04.1 LTS "Jammy Jellyfish" - Release amd64 (20220809.1)
SourcePackage: grub2
UpgradeStatus: No upgrade log present (probably fresh install)

[Julian Andres Klode (juliank)]

GRUB_DISTRIBUTOR and the other variables are set in /etc/default/grub on a normal system, but it seems you have inadvertently broken this file. I suggest having a look at that and fixing it, and reaching out to one of the support forums if you need further assistance.

[Vladimir S. (charchar8)]

Well, as this happened to me for the third time since I installed the machine, I'm in doubt I deleted the file intentionally.

I found the file was missing since 2024-02-04T07:34:56Z.

Well, actually, this other bug: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1879466 seems to be linked with this recent failure of mine because of the root cause was missing /etc/default/grub.

I restored the file from snapshot and will watch its presence closely.

Thanks a lot for your time!