netplan apply drops SSH connectivity on reboot

📖 ~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 networking fails after boot due to invalid netplan configuration.

Environment & Reproduction

Remote SSH sessions fail, interface has no expected IP, and default route is missing.

Root Cause Analysis

Use netplan get, netplan try, and journalctl -u systemd-networkd -b to inspect parser and runtime errors.

Quick Triage

Incorrect YAML indentation, wrong interface names, or renderer mismatch between NetworkManager and systemd-networkd.

Step-by-Step Diagnosis

Correct YAML under /etc/netplan, validate with netplan generate, then apply and confirm route and DNS settings.

Solution – Primary Fix

Check ip addr, ip route, and successful outbound name resolution after reboot.

Solution – Alternative Approaches

Use netplan try for remote servers so failed configs auto-revert without console intervention.

Verification & Acceptance Criteria

Restore prior netplan YAML from backup and run netplan apply from local console.

Rollback Plan

Template netplan files with tested interface mappings per VM profile.

Prevention & Hardening

netplan try; netplan generate; netplan apply; journalctl -u systemd-networkd -b

Related Errors & Cross-Refs

Attach /etc/netplan content, cloud-init network snippets, and interface inventory.

Related tutorial: View the step-by-step tutorial for Ubuntu 26.04 LTS.

View all Ubuntu 26.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Cloud images may regenerate network config unless cloud-init network management is controlled.