π ~1 min read
Table of contents
Symptom & Impact
Hostnames fail to resolve, breaking updates and external API connectivity.
Environment & Reproduction
Ubuntu 20.04 LTS using systemd-resolved with netplan-managed interfaces.
Root Cause Analysis
Resolver configuration, upstream DNS reachability, or resolv.conf linkage is incorrect.
Quick Triage
Verify IP connectivity first to isolate DNS-specific failures.
Step-by-Step Diagnosis
Inspect resolver status, active DNS servers, and symlink targets.
Solution – Primary Fix
Set valid nameservers in netplan and restart resolver services.
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Solution – Alternative Approaches
Apply per-interface DNS with resolvectl or network manager profiles.
Verification & Acceptance Criteria
DNS lookups and apt update succeed with expected response times.
Rollback Plan
Revert to prior netplan YAML and resolver settings from backup.
Prevention & Hardening
Use redundant DNS endpoints and monitor resolver health in logs.
Related Errors & Cross-Refs
Related to netplan syntax errors and default route misconfiguration.
Related tutorial: View the step-by-step tutorial for Ubuntu 20.04 LTS.
View all Ubuntu 20.04 LTS tutorials on the Tutorials Hub β
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
See man resolvectl, systemd-resolved docs, and Ubuntu networking guides.
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