Ubuntu 26.04 LTS – older kernels missing from GRUB menu – 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

GRUB does not show fallback kernels, reducing safe rollback options after bad updates.

Environment & Reproduction

Happens when old kernels are auto-removed or GRUB defaults hide submenu entries.

dpkg -l | grep linux-image
grep -E 'GRUB_' /etc/default/grub
grep menuentry /boot/grub/grub.cfg | head -n 30

Root Cause Analysis

Kernel retention policy or GRUB presentation settings remove visibility of advanced entries.

Quick Triage

Check installed kernel packages and whether advanced menu is generated.

ls /boot/vmlinuz-*
awk -F"'" '/menuentry / {print $2}' /boot/grub/grub.cfg | head -n 20

Step-by-Step Diagnosis

Inspect unattended autoremove behavior and apt history for kernel cleanup events.

grep -R autoremove /etc/apt/apt.conf.d
cat /var/log/apt/history.log | grep -i linux-image | tail -n 40
apt-mark showauto | grep linux

Solution – Primary Fix

Install an additional known-good kernel and regenerate GRUB menu entries.

sudo apt install linux-image-generic linux-headers-generic -y
sudo update-grub
sudo grub-set-default 0

Solution – Alternative Approaches

Adjust GRUB settings to always show menu and advanced options timeout.

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 update-grub

Verification & Acceptance Criteria

Accepted when GRUB menu contains current and fallback kernels.

grep menuentry /boot/grub/grub.cfg | grep -i ubuntu | head -n 30

Rollback Plan

Restore previous GRUB defaults if menu changes impact unattended boot behavior.

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

Prevention & Hardening

Keep at least one fallback kernel and review autoremove policy quarterly.

sudo apt-mark manual linux-image-generic
sudo apt autoremove --dry-run

Related Errors & Cross-Refs

Related issues include immediate reboot loops and inability to boot after regression in newest kernel.

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

GRUB manual, Ubuntu kernel lifecycle guidance, and apt autoremove policy docs.