📖 ~1 min read
Table of contents
Symptom & Impact
A jail refuses to boot and reports mount.fstab permission denied, blocking hosted services within that container.
Environment & Reproduction
service jail start exits with mount-related errors after configuration or dataset permission changes.
Root Cause Analysis
Invalid ownership on mount points, disallowed mount flags, or securelevel and allow.mount settings mismatch are frequent causes.
Quick Triage
Run jail -cv, verify jail.conf parameters, and inspect /etc/fstab. for invalid paths or options.
Step-by-Step Diagnosis
Confirm source and target mount directories exist, then validate jail permissions and mount policy settings. image_ref=0
Solution – Primary Fix
Correct jail.conf allow.mount flags, fix directory ownership, and update fstab entries to supported nullfs options. image_ref=1
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Solution – Alternative Approaches
Use basejail templates with read-only nullfs mounts to avoid custom per-jail mount complexity.
Verification & Acceptance Criteria
Jail starts cleanly, mounted paths are visible inside the jail, and no startup errors appear in logs.
Rollback Plan
Restore previous jail.conf and fstab files from backup, then restart jail service to return to known-good state.
Prevention & Hardening
Version-control jail configuration and apply preflight validation scripts before production jail restarts.
Related Errors & Cross-Refs
May coincide with devfs ruleset errors, denied mount syscalls, and immutable flag conflicts on target directories.
Related tutorial: View the step-by-step tutorial for freebsd-12.
View all freebsd-12 tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Consult man jail, man jail.conf, man mount_nullfs, and FreeBSD jail management documentation.
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