RHEL 7 boots old kernel after yum update due to grub default mismatch

📖 ~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

After successful yum kernel update and reboot, system still runs old kernel. Security fixes and driver updates are not active, causing compliance and supportability concerns.

Environment & Reproduction

Occurs when grub default entry is pinned to older kernel, or bootloader config regeneration failed. Reproduce by setting stale GRUB_DEFAULT and performing kernel update/reboot cycle.

Root Cause Analysis

Kernel packages install correctly, but bootloader selection remains on an older menuentry. Inconsistent grub2 config path updates between BIOS/UEFI can also keep outdated defaults.

Quick Triage

Compare rpm -q kernel list, uname -r, and grub2-editenv output. Inspect journalctl -b for boot entry clues and verify /etc/default/grub plus generated grub.cfg consistency.

Step-by-Step Diagnosis

Determine active firmware path, enumerate grub menu entries, and map configured default index/title to installed kernels. Confirm kernel-install scripts completed during yum transaction.

Solution – Primary Fix

Set correct default with grub2-set-default, regenerate grub config for proper platform path, reboot, and validate uname -r. Ensure systemctl reboot sequence completes without interruption.

Solution – Alternative Approaches

Use saved_entry mode with controlled automation, remove obsolete kernels to reduce selection errors, or enforce default kernel policy through configuration management.

Verification & Acceptance Criteria

Post-reboot kernel version must match target package. journalctl boot logs should show expected kernel command line and no fallback to prior entry.

Rollback Plan

If new kernel is unstable, select previous entry intentionally and document temporary rollback. Reassess driver/module compatibility before setting new default again.

Prevention & Hardening

Automate kernel update verification, standardize grub config regeneration steps, and audit default entry drift. Keep incident checks in maintenance playbooks after each yum kernel update.

Related Errors & Cross-Refs

Related issues include missing initramfs for newest kernel and failed dkms module load. Cross-reference package post-install scripts and bootloader path correctness.

Related tutorial: View the step-by-step tutorial for rhel-7.

View all rhel-7 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Consult RHEL bootloader management docs, grub2 manuals, and kernel lifecycle guidance. Capture approved update and rollback sequences for operations teams.