🟡 Medium   ⏱ 5–30 min  Last verified: 19 May 2026

📖 ~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 can ping IPs but cannot resolve domain names, breaking apt, APIs, and service discovery.

Environment & Reproduction

Ubuntu 20.04 with systemd-resolved and netplan-provided DNS entries.

Root Cause Analysis

Broken upstream DNS servers, stale /etc/resolv.conf symlink, or incorrect split DNS settings.

Quick Triage

Run ‘resolvectl status’, ‘ls -l /etc/resolv.conf’, and test with ‘dig @ ubuntu.com’.

Step-by-Step Diagnosis

Inspect network-specific DNS in netplan, check resolved service logs via journalctl, and verify route reachability.

Illustrative mockup for ubuntu-20-04-lts — ubuntu2004-cp08-dns-resolved-diagnose.webp
Debugging systemd-resolved DNS failures — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Restore correct resolv.conf symlink, set valid DNS in netplan, then ‘sudo systemctl restart systemd-resolved’.

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Illustrative mockup for ubuntu-20-04-lts — ubuntu2004-cp08-dns-resolved-fix.webp
Fixing resolvectl and netplan DNS settings — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Temporarily set public resolvers for continuity or deploy local caching resolver with health checks.

Verification & Acceptance Criteria

Domain lookup succeeds consistently and apt update completes with no name-resolution errors.

Rollback Plan

Reapply previous DNS configuration and restart networking if new resolver choice degrades latency.

Prevention & Hardening

Use redundant DNS servers, monitor query failure rates, and document resolver ownership.

Temporary failure in name resolution, Could not resolve host, and systemd-resolved timeout logs.

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

systemd-resolved documentation, netplan DNS examples, and Ubuntu networking troubleshooting guide.

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