Ubuntu 18.04 LTS Swap Not Activating After Reboot

📖 ~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

Memory pressure causes OOM kills because expected swap space is inactive.

Environment & Reproduction

Ubuntu 18.04 with manual swap changes, resized disks, or stale fstab entries.

Root Cause Analysis

Broken fstab mapping, invalid UUID, or missing swapfile prevents automatic activation.

Quick Triage

Check swapon summary, free output, and fstab entries to confirm swap activation state.

Step-by-Step Diagnosis

Verify swap file or partition exists, validate UUIDs, and inspect boot logs for mount errors.

Solution – Primary Fix

Create or repair swap resource, update fstab correctly, run swapon -a, and reboot to validate persistence.

Solution – Alternative Approaches

Tune swappiness or add zram if persistent disk swap is constrained.

Verification & Acceptance Criteria

Swap appears active after reboot and memory pressure no longer triggers early OOM events.

Rollback Plan

Revert to previous fstab and disable new swap resource if instability occurs.

Prevention & Hardening

Track memory trends and validate swap status in post-maintenance health checks.

Related Errors & Cross-Refs

Related symptoms include unexpected process kills and degraded database behavior under load.

Related tutorial: View the step-by-step tutorial for Ubuntu 18.04 LTS.

View all Ubuntu 18.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

See Ubuntu memory management guidance and Linux swap administration references.