π ~1 min read
Table of contents
Symptom & Impact
Server loses network after configuration changes, breaking SSH access and service availability.
Environment & Reproduction
Ubuntu 18.04 systems using netplan and systemd-networkd are vulnerable to YAML syntax mistakes.
Root Cause Analysis
Incorrect indentation, interface names, or routes prevent netplan from generating valid backend config.
Quick Triage
Use local console access, inspect interface state, and check netplan generate output for parser errors.
Step-by-Step Diagnosis
Validate YAML syntax, compare NIC names with ip link, and inspect networkd journal errors.
Solution – Primary Fix
Correct netplan YAML, apply configuration safely, and restart network stack if runtime state is stale.
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Solution – Alternative Approaches
Adopt templated netplan profiles and preflight linting in change automation.
Verification & Acceptance Criteria
Interface, route, DNS, and SSH remain healthy after apply and reboot.
Rollback Plan
Reapply last known-good netplan file from backup and restart networking services.
Prevention & Hardening
Require netplan try for remote edits and maintain validated baseline network templates.
Related Errors & Cross-Refs
Similar failures include DNS misrouting and cloud-init overwriting network configuration.
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
Review netplan examples and Ubuntu server networking documentation.
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