FreeBSD 15 – UFS filesystem mounts read-only after unclean shutdown – 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

Critical partitions mount read-only, preventing application writes and updates.

Environment & Reproduction

Typically follows abrupt power loss or kernel panic.

mount
dmesg | tail -n 80
fsck -N /dev/ada0p2

Root Cause Analysis

Filesystem consistency flags require fsck before safe read-write remount.

Quick Triage

Determine impacted partitions and whether metadata damage is isolated.

cat /etc/fstab
mount -p
fsck -fy -t ufs /dev/ada0p2

Step-by-Step Diagnosis

Boot single-user, run fsck pass-by-pass, and inspect unresolved inode issues.

shutdown now
fsck -fy
dmesg | grep -i ufs

Solution – Primary Fix

Repair UFS metadata then remount and restore normal multi-user operation.

fsck -fy /dev/ada0p2
mount -u -o rw /
exit

Solution – Alternative Approaches

Restore from backup if fsck cannot recover damaged structures safely.

dumpfs /dev/ada0p2 | head
restore -rf /backup/ufs-root.dump

Verification & Acceptance Criteria

Filesystem remains read-write after reboot and services recover.

reboot
mount | grep ' on / '
touch /var/tmp/ufs_rw_test

Rollback Plan

Boot from rescue media and restore snapshot if post-fsck behavior is unstable.

beadm list 2>/dev/null || true

Prevention & Hardening

Use UPS protection and clean shutdown policy to reduce unclean filesystem states.

sysctl kern.sync_on_panic
service powerd status

Related Errors & Cross-Refs

May occur with journal replay failures and disk controller timeouts.

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 UFS maintenance and fsck operational guides.