FreeBSD 15 – Crash Dumps Not Generated After Kernel Panic – dumpdev Configuration Repair

📖 ~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

No vmcore-style crash dump is available after panic, preventing root-cause analysis.

Environment & Reproduction

Systems with savecore disabled or dumpdev misconfigured.

dumpon -l
sysrc dumpdev
service savecore onestatus

Root Cause Analysis

Kernel dump device is unset or inaccessible, so panic dump cannot be written.

Quick Triage

Verify configured dump device and savecore state.

swapinfo -h
ls /var/crash

Step-by-Step Diagnosis

Review boot-time dump messages and dumpdev binding.

dmesg | grep -i dump
tail -n 150 /var/log/messages

Solution – Primary Fix

Configure dumpdev, enable savecore, and persist settings across reboot.

sysrc dumpdev=AUTO
service dumpon start
sysrc savecore_enable=YES
service savecore start

Solution – Alternative Approaches

Use dedicated dump partition sizing for large-memory systems.

Verification & Acceptance Criteria

dumpon reports active target and savecore captures dumps on next panic event.

dumpon -l
ls -lah /var/crash

Rollback Plan

Disable new dump settings if they interfere with swap sizing strategy.

Prevention & Hardening

Audit dump configuration after kernel and disk layout changes.

Related Errors & Cross-Refs

dump device not configured, no crash dump written, savecore skipped.

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

dumpon(8), savecore(8), and FreeBSD crash dump analysis workflow.