Debian 9 – resolv.conf Keeps Reverting and DNS Fails – Resolver Control

📖 ~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 lookups fail intermittently and resolv.conf keeps changing after renewals or reboot.

Environment & Reproduction

Seen when multiple resolver managers compete to write DNS settings on Debian 9.

Root Cause Analysis

Conflicting resolver stacks overwrite nameservers and search domains unexpectedly.

Quick Triage

Identify current resolv.conf owner and active resolver service before manual edits.

Step-by-Step Diagnosis

Trace symlink targets, inspect DHCP hooks, and validate effective DNS servers with dig.

Solution – Primary Fix

Select one resolver stack, disable competing writers, and enforce a single DNS policy.

Solution – Alternative Approaches

Use static resolver entries for isolated hosts without dynamic DNS requirements.

Verification & Acceptance Criteria

resolv.conf remains stable and forward/reverse lookups succeed across reboots.

Rollback Plan

Re-enable previous resolver service if application behavior depends on its local cache.

Prevention & Hardening

Document resolver ownership and audit hosts for DNS stack drift.

Related Errors & Cross-Refs

Temporary failure in name resolution, SERVFAIL spikes, and resolver overwrite conflicts.

Related tutorial: View the step-by-step tutorial for Debian 9.

View all Debian 9 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Debian resolver integration docs and DHCP client hook documentation.