FreeBSD 15 swapinfo Shows Zero Swap After Boot

📖 ~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 process kills sooner because swap is unavailable.

Environment & Reproduction

Often occurs after disk migration or partition table changes.

swapinfo -h

Root Cause Analysis

Configured swap device no longer matches actual disk identifiers.

Quick Triage

Confirm configured swap entries and current block devices.

cat /etc/fstab && gpart show

Step-by-Step Diagnosis

Test manual swapon on candidate devices and review boot logs.

sudo swapon -aL && dmesg | grep -i swap

Solution – Primary Fix

Update /etc/fstab with correct swap provider and enable immediately.

sudo ee /etc/fstab && sudo swapon -a

Solution – Alternative Approaches

Use swapfile on ZFS with recommended tuning when partition swap is unavailable.

Verification & Acceptance Criteria

swapinfo reports expected size and paging behavior stabilizes.

Rollback Plan

Restore prior fstab and reboot into known-good disk mapping.

Prevention & Hardening

Use labels/UUID-style identifiers and validate at boot checks.

Related Errors & Cross-Refs

May pair with loader prompt after failed root/swap detection.

Related tutorial: View the step-by-step tutorial for freebsd-15.

View all freebsd-15 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

FreeBSD memory and swap administration documentation.