PuTTY Troubleshooting Guide

Step-by-step solutions for common PuTTY problems and errors

Quick Diagnostic Checklist

Before troubleshooting, verify:

  • Server is running and accessible
  • Correct hostname/IP address
  • Correct port number (usually 22)
  • Valid username and credentials
  • No firewall blocking connection
  • Internet connectivity working
  • Latest PuTTY version installed
  • SSH service running on server

Connection Issues

❌ "Network error: Connection refused"

Possible Causes:

  • • SSH service not running on the server
  • • Wrong port number (SSH usually uses port 22)
  • • Firewall blocking the connection
  • • Server not listening on the specified interface

Solutions:

  1. 1. Verify SSH service: Contact server admin to ensure SSH is running
  2. 2. Check port: Try common SSH ports: 22, 2222, or ask admin
  3. 3. Test with telnet: Run telnet hostname 22
  4. 4. Check firewall: Temporarily disable Windows Firewall to test

❌ "Network error: Connection timed out"

Possible Causes:

  • • Network connectivity issues
  • • Incorrect hostname or IP address
  • • Firewall or router blocking traffic
  • • Server behind NAT without port forwarding

Solutions:

  1. 1. Test connectivity: Run ping hostname
  2. 2. Verify address: Double-check hostname/IP is correct
  3. 3. Try different network: Test from another location/network
  4. 4. Check proxy settings: Ensure PuTTY proxy settings are correct
  5. 5. Increase timeout: Go to Connection and increase timeout value

❌ Connection drops frequently

Solutions:

  1. 1. Enable keepalives: Connection → Set "Seconds between keepalives" to 30
  2. 2. Disable Nagle's algorithm: Connection → TCP → Check "Disable Nagle's algorithm"
  3. 3. Adjust TCP settings: Connection → TCP → Check "Enable TCP keepalives"
  4. 4. Change cipher: SSH → Encryption → Move AES to top of list

Authentication Issues

🔑 "Access denied" or "Authentication failed"

For Password Authentication:

  1. 1. Verify credentials: Double-check username and password
  2. 2. Check caps lock: Passwords are case-sensitive
  3. 3. Try auto-login: Connection → Data → Enter username
  4. 4. Check server config: Password auth might be disabled

For Key Authentication:

  1. 1. Check key format: Use .ppk files generated by PuTTYgen
  2. 2. Verify key path: SSH → Auth → Browse to correct .ppk file
  3. 3. Check server setup: Public key must be in ~/.ssh/authorized_keys
  4. 4. Verify permissions: ~/.ssh (700), authorized_keys (600)

🔑 "Server refused our key"

Step-by-Step Fix:

  1. 1. Check public key on server:
    cat ~/.ssh/authorized_keys
  2. 2. Verify permissions:
    chmod 700 ~/.ssh && chmod 600 ~/.ssh/authorized_keys
  3. 3. Check SSH server logs:
    sudo tail -f /var/log/auth.log
  4. 4. Regenerate keys: Use PuTTYgen to create new key pair
  5. 5. Test with verbose output: Enable SSH → Protocol → Verbose output

🔑 Converting OpenSSH keys to PuTTY format

  1. 1. Open PuTTYgen
  2. 2. Click "Load" and select your OpenSSH private key
  3. 3. Change file filter to "All Files (*.*)" if needed
  4. 4. Click "Save private key" to create .ppk file
  5. 5. Use the .ppk file in PuTTY's SSH → Auth settings

Terminal Display Issues

🖥️ Characters displaying incorrectly

Solutions:

  1. 1. Set character encoding: Window → Translation → UTF-8
  2. 2. Change font: Window → Appearance → Select Unicode font (e.g., Consolas)
  3. 3. Check locale: Run locale on server
  4. 4. Set LANG variable: export LANG=en_US.UTF-8

🖥️ Colors not displaying properly

Solutions:

  1. 1. Enable xterm colors: Window → Colours → "Allow terminal to use xterm 256-colour mode"
  2. 2. Set terminal type: Connection → Data → Terminal-type string: "xterm-256color"
  3. 3. Check TERM variable: Run echo $TERM
  4. 4. Reset terminal: Type reset in terminal

🖥️ Special keys not working

Common Fixes:

Backspace/Delete:

Terminal → Keyboard →

  • • Try "Control-H" for backspace
  • • Try "Control-?" for delete
Function Keys:

Terminal → Keyboard →

  • • Set function keys to "Xterm R6"
  • • Enable "Application keypad"

Performance Issues

⚡ Slow connection or typing lag

Performance Optimizations:

  1. 1. Enable compression: SSH → Enable compression
  2. 2. Optimize cipher: SSH → Encryption → Move AES to top
  3. 3. Disable features: Turn off unnecessary visual effects
  4. 4. Reduce scrollback: Window → Lines of scrollback → Reduce to 2000
  5. 5. Change font: Use bitmap fonts for better performance

⚡ File transfer speed issues

Optimization Tips:

  • • Use PSCP with compression: pscp -C
  • • Try different cipher: pscp -cipher aes
  • • Increase batch size: pscp -batch
  • • Consider alternative tools like WinSCP for large transfers

Diagnostic Tools & Commands

Windows Commands

ping hostname - Test connectivity
telnet hostname 22 - Test SSH port
nslookup hostname - Check DNS resolution
netstat -an | find "22" - Check listening ports

PuTTY Options

Enable "Event Log" - Window → Event Log
Verbose SSH output - SSH → Protocol options
Session logging - Session → Logging
Raw protocol logging - All session output

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