Ubuntu 20.04 LTS Common Problem 149 – Definitive Diagnosis, Recovery, and Prevention

📖 ~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

Hostnames fail to resolve while direct IP connectivity may still work.

Environment & Reproduction

Browsers and package tools report temporary name resolution errors under normal connectivity.

Root Cause Analysis

Resolver misconfiguration, unstable upstream DNS, cache corruption, or split-DNS conflicts.

Quick Triage

Test DNS queries against multiple resolvers and verify local gateway reachability first.

Step-by-Step Diagnosis

Check resolvectl status, /etc/resolv.conf symlink target, and run dig against known domains.

Solution – Primary Fix

Set reliable DNS servers in Netplan or NetworkManager and restart resolver services.

Solution – Alternative Approaches

Use local caching resolver with validated upstream redundancy for improved stability.

Verification & Acceptance Criteria

Name resolution remains stable for web browsing, updates, and internal service endpoints.

Rollback Plan

Revert manual resolver edits and restore prior network configuration files.

Prevention & Hardening

Standardize DNS configuration and monitor resolver failures with centralized logging alerts.

Related Errors & Cross-Refs

Often appears with apt mirror failures, VPN split-tunnel issues, and captive portal transitions.

Related tutorial: View the step-by-step tutorial for Ubuntu 20.04 LTS.

View all Ubuntu 20.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Consult systemd-resolved, Netplan, and Ubuntu network troubleshooting resources.