Ubuntu 22.04 LTS – SSH public key auth fails with permission denied – 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

Key-based login fails, forcing password fallback or blocking automated access workflows.

Environment & Reproduction

Typical after user home migrations or incorrect file permission inheritance.

Root Cause Analysis

Incorrect ownership, mode bits, or invalid authorized_keys content prevents key acceptance.

Quick Triage

Inspect SSH log entries and key file permissions on the target host.

Step-by-Step Diagnosis

Verify effective sshd settings and key matching for the connecting principal.

Solution – Primary Fix

Set strict permissions and ownership, then reload sshd configuration.

Solution – Alternative Approaches

Temporarily enable password auth only for emergency access under approved controls.

Verification & Acceptance Criteria

Public key login succeeds without prompting for password on trusted clients.

Rollback Plan

Restore prior authorized_keys and sshd_config backups if authentication regressions continue.

Prevention & Hardening

Enforce SSH key permission checks through account provisioning automation.

Related Errors & Cross-Refs

Closely related to connection refused cases and account lockout policy conflicts.

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

OpenSSH authorized_keys permission model and Jammy hardening recommendations.