Ubuntu 26.04 LTS – SSH login fails due to incorrect permissions on ~/.ssh – 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

Public key authentication fails and users are denied shell access.

Environment & Reproduction

Seen after manual file copy or home directory migration.

ssh -v user@host
sudo systemctl status ssh
ls -ld ~/.ssh

Root Cause Analysis

Loose permissions on home, .ssh, or authorized_keys cause sshd to reject keys.

Quick Triage

Check effective permissions and ownership across auth files.

namei -l ~/.ssh/authorized_keys
stat ~/.ssh ~/.ssh/authorized_keys
sudo tail -n 80 /var/log/auth.log

Step-by-Step Diagnosis

Trace server-side key acceptance and permission checks.

sudo sshd -T | grep -Ei 'pubkeyauthentication|authorizedkeysfile'
ls -la ~/.ssh
sudo journalctl -u ssh -n 100

Solution – Primary Fix

Set strict ownership and permissions, then restart SSH service.

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
chown -R $USER:$USER ~/.ssh
sudo systemctl restart ssh

Solution – Alternative Approaches

Temporarily enable password auth during emergency recovery with strict controls.

sudoedit /etc/ssh/sshd_config
sudo sshd -t
sudo systemctl restart ssh

Verification & Acceptance Criteria

SSH key login works and auth logs show accepted public key entries.

ssh -o PreferredAuthentications=publickey user@host
sudo grep -i 'Accepted publickey' /var/log/auth.log | tail -n 5

Rollback Plan

Restore previous sshd_config and key files if hardening breaks access patterns.

sudo cp /etc/ssh/sshd_config.bak /etc/ssh/sshd_config
sudo systemctl restart ssh

Prevention & Hardening

Enforce permission checks in provisioning scripts and periodic compliance scans.

find /home -maxdepth 2 -name .ssh -type d -exec ls -ld {} ;

Related Errors & Cross-Refs

Related to expired keys, disabled PubkeyAuthentication, and shell restrictions.

Related tutorial: View the step-by-step tutorial for Ubuntu 26.04 LTS.

View all Ubuntu 26.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Ubuntu OpenSSH server documentation and secure key management best practices.