User Authentication Failures - Troubleshooting Guide

User Authentication Failures - Troubleshooting Guide

Users can't log in, authentication is failing, access is denied. This guide gives you immediate steps to diagnose and fix user authentication failures—now. No theory, just action.

For setting up monitoring to prevent this in the future, see User Activity and Authentication Logs Monitoring Guide after you've resolved the immediate crisis.

60-Second Triage

Run these commands in order:

# Step 1: Check authentication logs (takes 10 seconds)
sudo grep "Failed password" /var/log/auth.log | tail -20

# Step 2: Check account status (takes 5 seconds)
passwd -S username

# Step 3: Verify account exists (takes 5 seconds)
id username

# Step 4: Check account lock status (takes 5 seconds)
grep username /etc/shadow

Common Authentication Issues and Quick Fixes

Symptoms of Authentication Failures

Authentication failures manifest in several ways:

• Login denied: Users can't log in with valid credentials
• Account locked: Accounts are locked after failed attempts
• Password expired: Passwords have expired and need reset
• Access denied: Users get "access denied" errors

Step-by-Step Troubleshooting

Step 1: Identify Authentication Failures

When users can't authenticate:

1. Check Authentication Logs:

   sudo grep "Failed password" /var/log/auth.log | tail -20
   

2. View Account Status:

   passwd -S username
   

3. Check Account Information:

   id username
   chage -l username
   

Step 2: Investigate Account Issues

Once you identify authentication failures:

1. Check Account Lock Status:

   grep username /etc/shadow | awk -F: '{print $2}'
   

2. Verify Account Expiration:

   chage -l username | grep "Account expires"
   

3. Check Account Disabled:

   grep username /etc/passwd | awk -F: '{print $7}'
   

Step 3: Fix Authentication Issues

When authentication issues are identified:

1. Unlock Account:

   sudo passwd -u username
   

2. Reset Password:

   sudo passwd username
   

3. Enable Account:

   sudo usermod -U username
   

4. Fix SSH Keys:

   chmod 600 ~/.ssh/authorized_keys
   chmod 700 ~/.ssh
   

Step 4: Prevent Future Authentication Failures

To prevent authentication failures:

1. Monitor Authentication Continuously:

   • Use Zuzia.app to monitor authentication logs
   • Set up alerts for authentication failures
   • Track authentication patterns

2. Configure Account Policies:

   • Set appropriate password policies
   • Configure account lockout policies
   • Monitor account expiration

Automatic Detection with Zuzia.app

Zuzia.app automatically monitors authentication and detects failures:

• Checks authentication logs every few minutes
• Detects authentication failures immediately
• Sends alerts when authentication fails
• Tracks authentication patterns over time

Set up authentication monitoring in Zuzia.app to prevent failures:

1. Add scheduled task: sudo grep "Failed password" /var/log/auth.log | tail -20
2. Configure alerts for authentication failures
3. Monitor authentication continuously

Best Practices for Preventing Authentication Failures

1. Monitor Authentication Continuously

Don't wait for authentication failures:

• Use Zuzia.app for continuous authentication monitoring
• Set up alerts before authentication issues become critical
• Review authentication logs regularly

2. Configure Account Policies

Set appropriate account policies:

• Configure password expiration policies
• Set account lockout thresholds
• Monitor account status

3. Respond Quickly to Authentication Issues

Have response procedures ready:

• Define escalation procedures for authentication failures
• Prepare account recovery procedures
• Test authentication recovery regularly

FAQ: Common Questions About Authentication Failures

How do I know if authentication is failing?

Check authentication logs: sudo grep "Failed password" /var/log/auth.log | tail -20. Check account status: passwd -S username. Verify account exists: id username.

What should I do immediately when authentication fails?

Immediately check authentication logs: sudo grep "Failed password" /var/log/auth.log | tail -20. Check account status: passwd -S username. Unlock account if locked: sudo passwd -u username. Reset password if needed: sudo passwd username.

Can authentication failures indicate security issues?

Yes, multiple authentication failures can indicate brute force attacks or unauthorized access attempts. Monitor authentication logs for patterns.

How can Zuzia.app help prevent authentication failures?

Zuzia.app monitors authentication logs continuously, detects authentication failures immediately, sends alerts when authentication fails, and tracks authentication patterns over time.

Related guides, recipes, and problems

• Related guides

  • User Activity and Authentication Logs Monitoring Guide
  • Server Security Events Monitoring and Intrusion Detection

• Related recipes

  • Monitor User Login Activity
  • Monitor System User Account Changes

• Related problems

  • Server Security Events and Intrusion Detection
  • Configuration Drift Causing Issues