🟠 High   ⏱ 5–30 min  Last verified: 19 May 2026
Affected versions: Ubuntu 24.04 LTS

📖 ~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

Repository hostnames fail to resolve and package updates cannot be downloaded.

Environment & Reproduction

Typically appears after network, DHCP, or DNS policy changes.

sudo apt update

Root Cause Analysis

systemd-resolved or upstream DNS servers are misconfigured or unavailable.

Quick Triage

Confirm resolver status and hostname lookup behavior.

resolvectl status
getent hosts archive.ubuntu.com

Step-by-Step Diagnosis

Inspect network route, resolver logs, and interface DNS assignment.

ip route
sudo systemctl status systemd-resolved
sudo journalctl -u systemd-resolved -n 80
Illustrative mockup for ubuntu-24-04-lts — dns_diag
DNS failures preventing repository access — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Set valid DNS servers in netplan and reapply networking configuration.

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sudo netplan apply
resolvectl flush-caches
sudo apt update
Illustrative mockup for ubuntu-24-04-lts — dns_fix
Resolver and netplan remediation steps — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Apply temporary resolver override for urgent patch windows.

sudo resolvectl dns eth0 1.1.1.1 8.8.8.8

Verification & Acceptance Criteria

Name resolution works and apt index updates complete successfully.

resolvectl query archive.ubuntu.com
sudo apt update

Rollback Plan

Restore previous netplan configuration from backup and reapply.

sudo cp /etc/netplan/01-netcfg.yaml.bak /etc/netplan/01-netcfg.yaml
sudo netplan apply

Prevention & Hardening

Use redundant DNS servers and monitor resolver health in baseline checks.

Often appears with proxy misconfiguration and IPv6 routing issues.

Related tutorial: View the step-by-step tutorial for Ubuntu 24.04 LTS.

View all Ubuntu 24.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Ubuntu systemd-resolved and netplan operational documentation.

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