🔴 Critical   ⏱ 5–30 min  Last verified: 20 May 2026
Affected versions: FreeBSD 15

📖 ~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

Host reboots into panic loop after update, creating a high-severity availability incident.

Environment & Reproduction

Usually follows kernel patch plus third-party module or driver mismatch.

freebsd-version -k -u
dmesg -a | tail -n 120
ls /var/crash

Root Cause Analysis

Kernel and loaded modules diverge in ABI or hardware-specific code path triggers fault post-update.

Quick Triage

Boot known-good environment and preserve crash dump for analysis.

nextboot -D
reboot
savecore -v /var/crash

Step-by-Step Diagnosis

Analyze vmcore stack trace and identify offending module or call path.

kgdb /boot/kernel/kernel /var/crash/vmcore.0 -ex 'bt' -ex 'quit'
kldstat
Illustrative mockup for freebsd-15 — terminal_or_shell
Collecting panic backtrace and crash dump metadata — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Disable problematic module, align kernel/userland versions, and apply tested patch set.

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sysrc kld_list=''
freebsd-update install
reboot
Illustrative mockup for freebsd-15 — log_or_config
Reverting boot environment and isolating culprit — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Use previous boot environment or rollback snapshot while vendor patch is validated.

Verification & Acceptance Criteria

System boots reliably with no new panic entries and normal workload starts.

uptime
dmesg | grep -i panic || true
service -e | wc -l

Rollback Plan

Re-enable prior kernel set from boot menu if instability persists.

Prevention & Hardening

Stage updates, validate kernel modules, and keep crash dump pipeline operational.

Often associated with kldload failures and unsupported out-of-tree modules.

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

savecore(8), kgdb(1), and FreeBSD kernel debugging handbook sections.

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