Encountering the frustrating "connection refused" error when trying to SSH into a server on port 22? You're definitely not alone! This is a common issue, and thankfully, it's usually fixable. Let's dive into the reasons why you might be seeing this error and, more importantly, how to troubleshoot and resolve it, so you can get back to securely connecting to your remote servers.

Understanding the "Connection Refused" Error

When you attempt to connect to a server using SSH, your computer sends a connection request to the server on a specific port, typically port 22. If the server actively refuses the connection, it sends back a "connection refused" message. This doesn't mean the server is down, but rather that something is preventing it from accepting SSH connections on that port. Let's explore the common culprits.

• SSH Service Not Running: The most frequent cause is that the SSH daemon (sshd) isn't running on the remote server. Think of it as the gatekeeper not being at their post. The SSH daemon is the program that listens for incoming SSH connections and handles the authentication process. If it's not running, no one's home to answer the door.

• Firewall Issues: Firewalls act as security guards, controlling network traffic in and out of a system. A firewall might be configured to block incoming connections on port 22, effectively preventing SSH access. This could be a firewall on the server itself or a network firewall between your computer and the server.

• Incorrect Port: Although SSH typically uses port 22, it can be configured to use a different port. If the server is listening on a non-standard port and you're trying to connect to port 22, you'll get a "connection refused" error. Similarly, a misconfigured client may be attempting to connect to the wrong port.

• SSH Configuration Errors: The SSH daemon's configuration file (sshd_config) dictates how the SSH server operates. Errors in this file, such as explicitly denying access or misconfiguring listening addresses, can lead to connection refusals.

• Network Connectivity Problems: Although less common, basic network connectivity issues can sometimes manifest as "connection refused" errors. If your computer can't reach the server at all (due to routing problems, DNS issues, or a simple lack of internet connectivity), you might see this error.

Troubleshooting Steps

Okay, enough with the explanations. Let's get our hands dirty and fix this! Here’s a step-by-step guide to troubleshooting the "connection refused" error.

1. Verify SSH Service Status on the Server

This is always the first place to check. You need to ensure that the SSH daemon is actually running on the server. The exact commands vary depending on the operating system, but here are a few common ones:

• Linux (systemd): sudo systemctl status ssh or sudo systemctl status sshd

• Linux (SysVinit): sudo service ssh status or sudo service sshd status

• macOS: sudo launchctl list | grep ssh

If the service is stopped, start it using the appropriate command:

• Linux (systemd): sudo systemctl start ssh or sudo systemctl start sshd

• Linux (SysVinit): sudo service ssh start or sudo service sshd start

• macOS: sudo launchctl load -w /System/Library/LaunchDaemons/ssh.plist (if it's disabled)

After starting the service, try connecting again. If it still fails, proceed to the next step.

2. Check Firewall Settings

Firewalls are notorious for blocking SSH traffic. You need to ensure that your firewall allows incoming connections on port 22 (or whatever port SSH is configured to use).

• Linux (iptables):

  • To check if iptables is blocking port 22: sudo iptables -L | grep 22

  • To allow incoming connections on port 22: sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

  • Important: These changes are not persistent across reboots. You'll need to save the iptables rules to make them permanent. The method for saving rules varies depending on your distribution (e.g., sudo iptables-save > /etc/iptables/rules.v4 and then configure your system to load these rules on boot).

• Linux (firewalld):

  • To check if firewalld is blocking port 22: sudo firewall-cmd --list-all

  • To allow incoming connections on port 22: sudo firewall-cmd --add-port=22/tcp --permanent

  • Then, reload the firewall: sudo firewall-cmd --reload

• Windows Firewall:

  • Open "Windows Defender Firewall with Advanced Security."

  • In the left pane, click "Inbound Rules."

  • Look for a rule related to SSH. If it doesn't exist or is disabled, create a new rule:

    • Click "New Rule..." in the right pane.

    • Select "Port" and click "Next."

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    • Select "TCP" and enter "22" in the "Specific local ports" field. Click "Next."

    • Select "Allow the connection" and click "Next."

    • Choose when the rule applies (Domain, Private, Public) and click "Next."

    • Give the rule a name (e.g., "Allow SSH") and click "Finish."

After adjusting the firewall, try connecting again.

3. Verify the SSH Port

Double-check that you're connecting to the correct port. The default port is 22, but it might have been changed on the server. You can check the SSH configuration file (/etc/ssh/sshd_config) on the server to see what port it's listening on.

• Open the file with a text editor: sudo nano /etc/ssh/sshd_config

• Look for the line Port 22. If the port number is different, that's the port you need to use when connecting.

To specify a different port when connecting with SSH, use the -p option:

ssh -p <port_number> user@server_address

For example:

ssh -p 2222 user@server_address

4. Check SSH Configuration File (sshd_config)

The sshd_config file contains various settings that control how the SSH server operates. Incorrect settings can prevent connections.

• ListenAddress: Ensure that the ListenAddress directive is configured correctly. If it's set to a specific IP address, the SSH server will only listen for connections on that address. If you want it to listen on all interfaces, make sure it's set to 0.0.0.0 or commented out.

• AllowUsers/DenyUsers: These directives control which users are allowed or denied access via SSH. Make sure your username isn't accidentally denied.

• AllowGroups/DenyGroups: Similar to AllowUsers/DenyUsers, these directives control access based on group membership.

After making any changes to the sshd_config file, you need to restart the SSH service for the changes to take effect:

sudo systemctl restart ssh or sudo service ssh restart

5. Test Network Connectivity

Ensure that you can actually reach the server from your computer. Use the ping command to test basic network connectivity.

ping server_address

If you don't get a response, there might be a network issue preventing you from reaching the server. Check your internet connection, routing settings, and DNS configuration.

You can also use traceroute (or tracert on Windows) to trace the route your packets are taking to the server. This can help identify where the connection is failing.

6. Check for Host Key Verification Issues

Sometimes, the "connection refused" error can be misleading and actually indicate a host key verification problem. This happens when the server's SSH host key has changed, and your client is refusing to connect because it doesn't recognize the new key.

To resolve this, you can remove the old host key from your known_hosts file. The error message usually tells you which line in the file to remove. The known_hosts file is typically located in your ~/.ssh/ directory.

Open the known_hosts file with a text editor and delete the line mentioned in the error message. Then, try connecting again. You'll be prompted to verify the new host key.

Warning: Removing the host key disables host key verification for that server, which can make you vulnerable to man-in-the-middle attacks. Only do this if you're sure that the server is legitimate and the host key change was expected.

7. Consider SELinux (Security-Enhanced Linux)

If you're running SELinux, it might be interfering with SSH connections. SELinux is a security module in the Linux kernel that provides mandatory access control. It can sometimes block SSH traffic if it's not configured correctly.

To check if SELinux is enabled, run sestatus. If it's enabled, you can try temporarily disabling it to see if it's causing the problem:

sudo setenforce 0

This will set SELinux to permissive mode, which means it won't enforce its policies. If SSH connections start working after disabling SELinux, you'll need to configure SELinux to allow SSH traffic. The exact steps for doing this are beyond the scope of this article, but you can find plenty of resources online.

Important: Disabling SELinux can weaken your system's security. Only do this for troubleshooting purposes, and re-enable it as soon as possible.

Conclusion

The "connection refused" error can be a real head-scratcher, but by systematically working through these troubleshooting steps, you should be able to identify and resolve the underlying issue. Remember to start with the most common causes (SSH service status and firewall settings) and then move on to more advanced troubleshooting if necessary. With a little patience and persistence, you'll be back to securely connecting to your servers in no time! Good luck, and happy SSH-ing!