Permission denied (publickey) for valid SSH user

📖 ~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 login fails despite correct username and key pair expectations.

Environment & Reproduction

Ubuntu 16.04 servers with hardened SSH settings and key-based auth.

Root Cause Analysis

Key mismatch, file permission issues, or sshd auth policy blocks key acceptance.

Quick Triage

Inspect ssh client verbose output and server auth logs for rejection reason.

Step-by-Step Diagnosis

Check authorized_keys content, ownership, modes, and sshd authentication directives.

Solution – Primary Fix

Install correct public key, enforce strict file permissions, and reload sshd.

Solution – Alternative Approaches

Enable temporary password auth for break-glass access with strict controls.

Verification & Acceptance Criteria

Public key login succeeds and unauthorized keys remain rejected.

Rollback Plan

Reinstate previous SSH auth settings if new policy blocks critical automation.

Prevention & Hardening

Standardize key provisioning and continuously audit SSH file permissions.

Related Errors & Cross-Refs

Authentication refused bad ownership and Permission denied (publickey).

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 key authentication and Ubuntu account security documentation.