FreeBSD 15: Nginx returns 502 when php-fpm socket permissions drift

📖 ~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

Web requests fail with 502 responses, reducing availability for PHP-backed applications.

Environment & Reproduction

Often appears after php-fpm pool edits, service restarts, or file permission hardening changes.

Root Cause Analysis

Nginx worker user lacks permission to access the php-fpm Unix socket path.

Quick Triage

Check socket existence, ownership, mode, and process identities for nginx and php-fpm.

Step-by-Step Diagnosis

Analyze service logs and runtime socket metadata to pinpoint permission drift origin.

Solution – Primary Fix

Align pool and web server user/group settings, then reload both daemons safely.

Solution – Alternative Approaches

Switch to TCP loopback upstream with strict firewalling where socket ACLs are problematic.

Verification & Acceptance Criteria

502 errors disappear and application transactions complete successfully under load.

Rollback Plan

Revert to previous pool and nginx upstream settings if change introduces instability.

Prevention & Hardening

Track config drift with policy as code and validate service compatibility before restart.

Related Errors & Cross-Refs

Related to chroot path mismatches and stale socket files after abrupt process termination.

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

nginx and php-fpm docs plus FreeBSD service management references.