Ubuntu 22.04 LTS – Common Problem 003 – Diagnosis and Fix

📖 ~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

System loses network after reboot or netplan apply. SSH sessions drop and services cannot reach external dependencies.

Environment & Reproduction

Ubuntu 22.04 server using netplan with systemd-networkd or NetworkManager. Reproduce by introducing indentation errors in /etc/netplan/*.yaml.

Root Cause Analysis

Malformed YAML, wrong interface names, or mismatched renderer settings prevent netplan from generating valid backend configuration.

Quick Triage

Run sudo netplan generate and ip a. Confirm interface names with ip link and check current route table via ip route.

Step-by-Step Diagnosis

Validate syntax with sudo netplan –debug generate, inspect journalctl -u systemd-networkd -b, and compare applied config under /run/systemd/network.

Solution – Primary Fix

Correct YAML structure and interface names, then run sudo netplan try followed by sudo netplan apply. Ensure renderer matches deployment intent.

Solution – Alternative Approaches

Temporarily assign IP with ip addr add and ip route add for emergency access, then fix netplan persistently.

Verification & Acceptance Criteria

Interface receives expected IP, default route exists, DNS resolves, and reboot preserves connectivity without manual intervention.

Rollback Plan

Restore previous YAML from backup and reapply netplan. If remote, use console access to avoid lockout.

Prevention & Hardening

Use netplan try for remote hosts, keep versioned backups, and standardize interface naming conventions.

Related Errors & Cross-Refs

Error in network definition, unknown key in netplan YAML, interface not found.

Related tutorial: View the step-by-step tutorial for Ubuntu 22.04 LTS.

View all Ubuntu 22.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Ubuntu netplan documentation, man netplan, systemd-networkd man pages.