Debian 11: DNS resolution breaks after resolv.conf overwrite

📖 ~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

Name resolution fails because `/etc/resolv.conf` is overwritten by conflicting network services.

Environment & Reproduction

Hosts cannot resolve internal or external domains and package repositories become unreachable.

Root Cause Analysis

Check `cat /etc/resolv.conf`, run `resolvectl status` when available, and test `getent hosts deb.debian.org`.

Quick Triage

DHCP, NetworkManager, or local scripts rewrite resolver config without persistent policy control.

Step-by-Step Diagnosis

Set resolver ownership in the active network manager and define stable DNS servers and search domains.

Solution – Primary Fix

Verify `getent hosts`, `dig +short`, and application-level lookups all return expected results.

Solution – Alternative Approaches

Keep resolver policy in version control and block ad-hoc edits on production hosts.

Verification & Acceptance Criteria

Restore previous resolver config and restart the responsible network service.

Rollback Plan

Monitor resolver file checksum and DNS success rate for critical service domains.

Prevention & Hardening

`cat /etc/resolv.conf`; `getent hosts deb.debian.org`; `dig +short deb.debian.org`

Related Errors & Cross-Refs

Provide resolver configs, DHCP lease data, and packet captures if DNS responses are inconsistent.

Related tutorial: View the step-by-step tutorial for debian-11.

View all debian-11 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Mixed IPv4 and IPv6 resolver paths can create intermittent failures when one path is degraded.