CentOS Stream 9 – Common Problem 104 – Diagnosis and Fix

📖 ~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

DNS queries fail or hit 127.0.0.53 with NXDOMAIN unexpectedly.

Environment & Reproduction

Occurs when systemd-resolved is enabled alongside dnsmasq or NetworkManager DNS plugin.

Root Cause Analysis

Two stub resolvers compete for port 53 or rewrite /etc/resolv.conf.

Quick Triage

ss -lunp | grep ‘:53’ shows which process owns the port.

Step-by-Step Diagnosis

Check resolvectl status and /etc/resolv.conf symlink target.

Solution – Primary Fix

Pick one resolver: disable systemd-resolved or set NM dns=none with a fixed /etc/resolv.conf.

Solution – Alternative Approaches

Use dns=systemd-resolved in NetworkManager.conf for a unified path.

Verification & Acceptance Criteria

dig @127.0.0.53 example.com returns expected answers without warnings.

Rollback Plan

Re-enable previous resolver and restore /etc/resolv.conf from backup.

Prevention & Hardening

Pin DNS settings in Kickstart and avoid mixing dnsmasq with resolved.

Related Errors & Cross-Refs

Related: NetworkManager dispatcher issues and split-horizon DNS.

Related tutorial: View the step-by-step tutorial for centos-stream-9.

View all centos-stream-9 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

systemd-resolved(8) man page and NetworkManager docs.