π ~1 min read
Table of contents
Symptom & Impact
Host cannot resolve domain names, breaking updates and outbound services.
Environment & Reproduction
Ubuntu 20.04 with systemd-resolved enabled and custom DNS upstreams.
Root Cause Analysis
Broken upstream DNS entries or mislinked resolv.conf disrupt stub forwarding.
Quick Triage
Check resolvectl status, /etc/resolv.conf link target, and query failures.
Step-by-Step Diagnosis
Trace DNS path from application resolver to upstream server response.
Solution – Primary Fix
Set valid DNS servers, fix resolv.conf symlink, and restart systemd-resolved.
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Solution – Alternative Approaches
Configure netplan nameservers directly or deploy local caching resolver.
Verification & Acceptance Criteria
dig and getent hosts return expected records with low latency.
Rollback Plan
Revert resolver configuration to last known-good settings.
Prevention & Hardening
Monitor DNS health and maintain at least two reliable upstream resolvers.
Related Errors & Cross-Refs
Apt mirror failures and TLS endpoint errors often stem from DNS outages.
Related tutorial: View the step-by-step tutorial for Ubuntu 18.04 LTS.
View all Ubuntu 18.04 LTS tutorials on the Tutorials Hub β
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Ubuntu systemd-resolved and resolvectl usage documentation.
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