Ubuntu 18.04 LTS – SSH login rejected despite correct credentials

📖 ~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 authentication fails repeatedly, preventing administrative access.

Environment & Reproduction

Occurs after hardening changes to sshd config, PAM, or account policy settings.

Root Cause Analysis

Authentication method mismatch, account restrictions, or file permission errors block login.

Quick Triage

Confirm sshd status, review auth logs, and test with verbose SSH client output.

Step-by-Step Diagnosis

Inspect sshd effective config, key permissions, and PAM/account state.

Solution – Primary Fix

Align allowed auth methods, fix permissions, and reload sshd safely.

Solution – Alternative Approaches

Use console access to create emergency admin key-based account for recovery.

Verification & Acceptance Criteria

SSH login succeeds with approved methods and security policies remain enforced.

Rollback Plan

Restore previous sshd and PAM configs from validated backup snapshots.

Prevention & Hardening

Apply staged SSH changes with pre-checks and out-of-band access validation.

Related Errors & Cross-Refs

Permission denied, Authentication refused, and account is locked messages.

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

OpenSSH server hardening and Ubuntu authentication troubleshooting references.