Ubuntu 18.04 LTS – DNS resolution fails after netplan or resolv.conf changes

📖 ~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

Host cannot resolve domain names, causing package updates and service calls to fail.

Environment & Reproduction

Frequently occurs after manual edits to netplan YAML or resolver configuration files.

Root Cause Analysis

Incorrect nameserver settings, stub resolver mismatch, or malformed netplan config breaks DNS.

Quick Triage

Test raw IP connectivity and compare resolver status with configured DNS servers.

Step-by-Step Diagnosis

Inspect netplan, systemd-resolved state, and effective resolver paths.

Solution – Primary Fix

Correct DNS configuration, apply netplan safely, and restart resolver components.

Solution – Alternative Approaches

Set fallback resolvers or use static resolver config for emergency restoration.

Verification & Acceptance Criteria

Forward and reverse DNS lookups succeed and dependent services recover.

Rollback Plan

Revert to last known-good network YAML and resolver settings from backup.

Prevention & Hardening

Validate netplan syntax in CI and keep documented DNS ownership boundaries.

Related Errors & Cross-Refs

Temporary failure in name resolution and systemd-resolved timeout events.

Related tutorial: View the step-by-step tutorial for Ubuntu 18.04 LTS.

View all Ubuntu 18.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Ubuntu 18.04 netplan and systemd-resolved operational guidance.