Ubuntu 18.04 LTS – network interface is down after 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

Primary network interface stays down after boot, disrupting remote access and workloads.

Environment & Reproduction

Often seen after NIC rename changes, cloud-init edits, or netplan migration issues.

Root Cause Analysis

Interface name mismatch or invalid renderer config prevents link activation at startup.

Quick Triage

List interfaces, verify actual NIC names, and inspect applied network profiles.

Step-by-Step Diagnosis

Check boot logs, netplan definitions, and carrier state for target NIC.

Solution – Primary Fix

Update interface mapping, apply corrected netplan, and confirm auto-start settings.

Solution – Alternative Approaches

Temporarily bring interface up manually while permanent config is prepared.

Verification & Acceptance Criteria

Interface initializes on reboot with expected IP addressing and route availability.

Rollback Plan

Restore previous network YAML and cloud-init network config backups.

Prevention & Hardening

Pin predictable interface naming and validate network plans before reboot events.

Related Errors & Cross-Refs

Device not found, no-carrier, and failed to bring up interface errors.

Related tutorial: View the step-by-step tutorial for Ubuntu 18.04 LTS.

View all Ubuntu 18.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Ubuntu 18.04 network interface naming and netplan renderer documentation.