Ubuntu 22.04 LTS – swap does not activate after reboot – 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

Hosts with low RAM hit OOM pressure sooner because configured swap never comes online.

Environment & Reproduction

Occurs after disk cloning, UUID changes, or migration from swap file to partition.

Root Cause Analysis

fstab references stale UUID/path or swap file permissions are incorrect for activation.

Quick Triage

Check boot logs for swap mount failures and validate entry correctness.

Step-by-Step Diagnosis

Match swap UUIDs and verify file ownership/mode for swapfile-based setups.

Solution – Primary Fix

Update fstab with correct UUID or recreate swap file with required permissions.

Solution – Alternative Approaches

Use zram on constrained systems where disk-backed swap performance is poor.

Verification & Acceptance Criteria

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

Rollback Plan

Revert fstab to previous known-good entry and disable problematic new swap target.

Prevention & Hardening

Template swap configuration with UUID discovery and post-boot health checks.

Related Errors & Cross-Refs

Can coexist with low-memory service restarts and kernel OOM-killer events.

Related tutorial: View the step-by-step tutorial for Ubuntu 22.04 LTS.

View all Ubuntu 22.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Ubuntu swap configuration guide and memory management references.