Ubuntu 20.04 LTS – Common Problem 015 – Diagnosis and Fix

📖 ~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 update fails or new kernel not selectable, risking unbootable state after reboot.

Environment & Reproduction

Ubuntu 20.04 BIOS/UEFI systems with recent kernel update and custom boot settings.

Root Cause Analysis

Broken grub scripts, incorrect EFI mount, or package interruption during grub-common/grub-efi updates.

Quick Triage

Run ‘sudo update-grub’ and inspect errors; confirm EFI partition mounted at ‘/boot/efi’.

Step-by-Step Diagnosis

Check dpkg status for grub packages, verify disk identifiers, and review /etc/default/grub syntax.

Solution – Primary Fix

Reinstall/grub packages and regenerate config with ‘sudo grub-install’ then ‘sudo update-grub’.

Solution – Alternative Approaches

Use chroot from live media to repair bootloader when system cannot boot normally.

Verification & Acceptance Criteria

Reboot selects latest kernel and boot menu entries load without rescue prompts.

Rollback Plan

Boot previous kernel from GRUB advanced options and restore prior grub defaults.

Prevention & Hardening

Keep rescue media ready, snapshot before kernel/boot changes, and avoid manual script edits.

Related Errors & Cross-Refs

grub-probe failed, no such device, and initramfs prompt after kernel update.

Related tutorial: View the step-by-step tutorial for Ubuntu 20.04 LTS.

View all Ubuntu 20.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Ubuntu boot repair docs, GRUB manual, and EFI partition best practices.