FreeBSD 15: Jail startup failure from VNET epair exhaustion

📖 ~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

One or more jails fail at startup, leaving application tiers offline and dependency chains broken.

Environment & Reproduction

Appears on dense jail hosts where repeated start/stop cycles leak or consume virtual interfaces.

Root Cause Analysis

The host reaches epair or ifnet limits, preventing VNET allocation for additional jail instances.

Quick Triage

Count existing interfaces, identify stale pairs, and review jail management scripts for cleanup gaps.

Step-by-Step Diagnosis

Trace interface lifecycle events and jail logs to pinpoint exhaustion source and leak pattern.

Solution – Primary Fix

Remove stale interfaces, adjust limits, and restart affected jails in controlled order.

Solution – Alternative Approaches

Migrate selected jails to non-VNET mode or distribute workload across additional hosts.

Verification & Acceptance Criteria

All target jails start cleanly and network interfaces map correctly with no new allocation errors.

Rollback Plan

Revert recent jail networking changes and restore prior host-level tunables from backup.

Prevention & Hardening

Add automated stale interface cleanup and capacity alarms for interface count thresholds.

Related Errors & Cross-Refs

Frequently appears with bridge member overflow and rc order dependency issues.

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

jail.conf and ifconfig man pages plus VNET design notes from FreeBSD documentation.