Troubleshooting Common SSH Errors (Connection Refused, Timeout, Keys)

Secure Shell (SSH) is a crucial tool for remotely accessing servers. However, users may encounter various errors during connection attempts. This tutorial covers common SSH errors, including connection refused, connection timed out, and issues related to SSH keys, with steps to troubleshoot them effectively.

1. Connection Refused

If you encounter a “Connection refused” error, it typically means that the SSH service is not running on the server or is not configured to accept connections. Here are some steps to troubleshoot this issue:

• Check if SSH is installed: Ensure that the SSH server (usually OpenSSH) is installed on the server.

sudo apt install openssh-server   # For Ubuntu/Debian
sudo yum install openssh-server   # For CentOS/RHEL

• Verify SSH service status: Check if the SSH service is active and running with:

sudo systemctl status sshd

If it’s not running, start the service:

sudo systemctl start sshd

• Check SSH configuration: Look for errors in the SSH configuration file (/etc/ssh/sshd_config). Ensure that:
• The Port directive is properly set (default is 22).
• The ListenAddress directive is correctly configured.

After making changes, restart SSH:

sudo systemctl restart sshd

• Firewall settings: Ensure that your firewall allows SSH traffic. To allow SSH, you can use:

sudo ufw allow ssh   # For UFW

or

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT   # For iptables

2. Connection Timed Out

A “Connection timed out” error generally indicates network issues or firewall restrictions. To troubleshoot this error:

• Check network connectivity: Ensure that your client can reach the server by pinging the server IP:

ping server_ip_address

• Verify SSH port: Confirm that you are trying to connect to the correct port. If you changed the default port, include it in your SSH command:

ssh -p custom_port username@server_ip_address

• Firewall settings: Make sure your server’s firewall and any intermediate firewalls allow connections on the SSH port. Check firewall rules on the server, as mentioned earlier.

3. SSH Key Issues

If you’re having trouble with SSH keys, ensuring proper configuration is important. Follow these steps:

• Check for SSH key presence: Ensure your SSH keys are generated and located in the correct directory.

ls -l ~/.ssh/

• Correct permissions: Check the permissions of the .ssh directory and the key files. They should typically be:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_rsa
chmod 644 ~/.ssh/id_rsa.pub

• Adding your public key to the server: Ensure your public key (~/.ssh/id_rsa.pub) is added to the ~/.ssh/authorized_keys file on the server. You can use ssh-copy-id for simplicity:

ssh-copy-id username@server_ip_address

• Verbose mode: To get more information about the connection process, use verbose mode:

ssh -v username@server_ip_address

This command provides detailed output that can help diagnose issues.

4. Conclusion

Troubleshooting SSH connection issues can be straightforward if you follow the steps outlined above. Understanding the common errors such as connection refused, connection timeout, and key issues will help you quickly identify and resolve problems, ensuring secure and reliable access to your servers.

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Dorian Kane

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