📖 ~1 min read
Table of contents
Symptom & Impact
Package index retrieval fails because repository hostnames cannot be resolved.
Environment & Reproduction
Seen after network changes, resolver restarts, or stale DNS cache states.
Root Cause Analysis
DNS resolver path is broken between host configuration and upstream nameservers.
Quick Triage
Test DNS lookups, gateway reachability, and resolver service status quickly.
Step-by-Step Diagnosis
Trace name-resolution path from local resolver to upstream DNS servers.
Solution – Primary Fix
Correct resolver configuration and restart networking components cleanly.
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Solution – Alternative Approaches
Use fallback resolvers or local caching DNS as a controlled temporary measure.
Verification & Acceptance Criteria
Repository domains resolve consistently and apt update finishes successfully.
Rollback Plan
Revert to prior resolver configuration if new settings degrade connectivity.
Prevention & Hardening
Monitor DNS latency and enforce validated resolver templates fleet-wide.
Related Errors & Cross-Refs
Associated with mirror timeout and proxy misconfiguration failures.
Related tutorial: View the step-by-step tutorial for Debian 9.
View all Debian 9 tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Debian networking and DNS troubleshooting references.
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