Ubuntu 16.04 LTS – SSH login fails with Permission denied (publickey) – Fix & Prevention

📖 ~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

SSH key-based access fails, blocking remote administration.

Environment & Reproduction

Ubuntu 16.04 server with hardened SSH settings and user key auth.

Root Cause Analysis

Key mismatch, disabled auth method, or incorrect file permissions.

Quick Triage

Run ssh -vvv from client and inspect auth.log on server.

Step-by-Step Diagnosis

Verify authorized_keys contents, ownership, modes, and sshd config.

Solution – Primary Fix

Install correct public key, repair permissions, and reload sshd.

Solution – Alternative Approaches

Use temporary console access to recover account and SSH policies.

Verification & Acceptance Criteria

Key login succeeds and password fallback policy matches requirements.

Rollback Plan

Revert sshd_config from backup and restart service safely.

Prevention & Hardening

Use managed key deployment and periodic permission audits.

Related Errors & Cross-Refs

Host key mismatch and PAM account restrictions may co-occur.

Related tutorial: View the step-by-step tutorial for Ubuntu 16.04 LTS.

View all Ubuntu 16.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

OpenSSH server hardening and authentication troubleshooting docs.