Ubuntu 26.04 LTS – GRUB menu not shown and wrong kernel keeps booting – Fix & Prevention

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

System repeatedly boots an undesired kernel, complicating rollback and incident recovery.

Environment & Reproduction

Occurs when GRUB timeout style hides menu and default entry remains unchanged.

cat /etc/default/grub
uname -r

Root Cause Analysis

GRUB configuration hides menu and saved default entry points to a non-preferred kernel.

Quick Triage

Inspect GRUB defaults, available menu entries, and boot history.

grep -E 'GRUB_(TIMEOUT|TIMEOUT_STYLE|DEFAULT|SAVEDEFAULT)' /etc/default/grub
grep 'menuentry ' /boot/grub/grub.cfg | head -n 20

Step-by-Step Diagnosis

Identify target kernel menu index and current saved GRUB entry.

sudo grub-editenv list
grep -n 'menuentry ' /boot/grub/grub.cfg | head -n 30

Solution – Primary Fix

Enable menu display and set explicit default kernel entry.

sudo sed -i 's/^GRUB_TIMEOUT_STYLE=.*/GRUB_TIMEOUT_STYLE=menu/' /etc/default/grub
sudo sed -i 's/^GRUB_TIMEOUT=.*/GRUB_TIMEOUT=5/' /etc/default/grub
sudo grub-set-default 'Advanced options for Ubuntu>Ubuntu, with Linux '
sudo update-grub

Solution – Alternative Approaches

Use one-time kernel boot for testing without changing persistent default.

sudo grub-reboot 'Advanced options for Ubuntu>Ubuntu, with Linux '

Verification & Acceptance Criteria

GRUB menu appears and selected kernel persists across reboot.

sudo reboot
uname -r

Rollback Plan

Restore previous /etc/default/grub values and regenerate config.

sudo cp /etc/default/grub.bak /etc/default/grub
sudo update-grub

Prevention & Hardening

Keep at least one known-good kernel and document kernel pinning policy.

dpkg -l | grep linux-image
apt-mark showhold

Related Errors & Cross-Refs

Related to unattended-upgrades kernel transitions and initramfs regressions.

Related tutorial: View the step-by-step tutorial for Ubuntu 26.04 LTS.

View all Ubuntu 26.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Ubuntu GRUB administration and kernel rollback best practices.