Ubuntu 22.04 LTS – SSH login fails after hardening due to incorrect permissions – 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 login fails and administrators risk lockout.

Environment & Reproduction

Ubuntu 22.04 server with recent edits to ~/.ssh or /etc/ssh/sshd_config.

Root Cause Analysis

OpenSSH enforces strict ownership and permission checks on key files and home paths.

Quick Triage

Inspect auth log with journalctl -u ssh and run sshd -t for config validation.

Step-by-Step Diagnosis

Check permissions on home directory, .ssh directory, and authorized_keys file.

Solution – Primary Fix

Set chmod 700 ~/.ssh and chmod 600 ~/.ssh/authorized_keys with correct user ownership.

Solution – Alternative Approaches

Temporarily allow password authentication from trusted subnet while repairing key setup.

Verification & Acceptance Criteria

SSH key auth succeeds and sshd -t returns clean configuration output.

Rollback Plan

Revert sshd_config changes and restart ssh service from console session.

Prevention & Hardening

Use configuration management to enforce known-good SSH permissions and options.

Related Errors & Cross-Refs

PAM misconfiguration and fail2ban bans can present similar login failures.

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 22.04 OpenSSH server hardening and troubleshooting documentation.