How to Check If SSH Server Is Running on Linux? A Complete Guide

Abur Rahim

2 years ago

How to check if ssh server is running on linux? The Secure Shell (SSH) protocol is a widely used tool for remote access & administration of Linux systems. Whether you’re a systems administrator or just someone managing their own server, it’s important to verify that the SSH server is running properly. This guide will walk you through various methods of how to check if ssh server is running on Linux. By the end of this guide, you’ll have a comprehensive understanding of how to ensure your SSH server is operational.

Understanding SSH

SSH (Secure Shell) is a cryptographic network protocol that allows secure communication over an unsecured network. It’s commonly used for:

Remote login to servers.
Secure file transfers (eg, SCP or SFTP).
Running commands on remote systems.

The service responsible for handling incoming SSH connections is typically called sshd (the SSH daemon). Ensuring that sshd is active and running is crucial for the functioning of SSH on your system.

How to Check If SSH Server Is Running on Linux?

1. Checking the SSH Service Status

The most straightforward method to verify whether the SSH server is running is to check its service status using system management tools like systemctl or service.

Using systemctl (for systems with systemd)

On modern Linux distributions that use systemd, the systemctl command is your go-to tool for managing services. Here’s how you can check the status of the SSH service:

Open a terminal on the Linux system.
Run the following command:
```
bash copy code

sudo systemctl status ssh
```
Alternatively, on some distributions (like CentOS or Fedora), the service might be named sshd instead of ssh:
```
bash copy code

sudo systemctl status sshd
```

Look for output similar to this:

yaml Copy code

● ssh.service - OpenBSD Secure Shell server

Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)

Active: active (running) since Fri 2024-11-01 14:32:17 UTC; 1h 25min ago

Active: active (running) confirms the SSH server is running.
If the service is inactive or stopped, you can start it using:
```
bash Copy code

sudo systemctl start ssh
```
To ensure the SSH server starts automatically at boot, enable it:
```
bash Copy code

sudo systemctl enable ssh
```

Using service (for older systems without systemd)

On older Linux distributions, you can use the service command:

bash   Copy code
sudo service ssh status

Again, on some systems, the service name might be sshd:

bash   Copy code
sudo service sshd status

The output will indicate whether the SSH server is running or stopped.

2. Checking SSH Ports

The SSH server listens on a specific network port (default: port 22). You can verify if the port is open and the SSH server is listening using commands like netstat, ss, or lsof.

Using netstat
Run the following command to check for processes listening on port 22:

bash   Copy code
sudo netstat -tuln | grep :22

If the SSH server is active, you’ll see output similar to:

ruby   Copy code
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN

Using ss

The ss command provides similar functionality but is faster & more efficient:

bash   Copy code
sudo ss -tuln | grep :22

The output points that the SSH service is listening on port 22.

Using lsof

The lsof command can also help identify processes listening on port 22:

bash   Copy code
sudo lsof -i :22

You should see a process (likely sshd) bound to port 22.

3. Testing SSH Connectivity

Sometimes, the service might be running but not functioning as expected. Testing connectivity using the ssh command can help verify the server’s operational status.

Test Local Connection

From the server itself, you can try to connect to the SSH (Secure Shell) server:

bash   Copy code
ssh localhost

If SSH is working correctly, you’ll be prompted to log in.

Test Remote Connection

From another system, try connecting to the server’s IP address or hostname:

bash   Copy code
ssh username@server-ip

Replace username with your actual username and server-ip with the server’s IP address. If the connection is successful, the SSH server is running and accessible.

4. Checking Logs for Issues

If the SSH server isn’t working as expected, logs can provide valuable insights.

System Logs

On most Linux systems, the logs are stored in /var/log. Check the syslog or auth.log for SSH-related entries:

bash   Copy code
sudo tail -f /var/log/syslog

bash   Copy code
sudo tail -f /var/log/auth.log

Look for entries related to sshd. Errors or warnings here can help diagnose the issue.

Journalctl Logs (systemd systems)

For systems using systemd, you can use journalctl:

bash   Copy code
sudo journalctl -u ssh

Replace ssh with sshd if your service is named differently. Reviews the output for any errors or warnings.

5. Verifying Configuration

Incorrect SSH configuration can prevent the service from running properly. The configuration file for sshd is usually located at /etc/ssh/sshd_config. To check for errors in the configuration file, run:

bash   Copy code
sudo sshd -t

If there are any syntax errors, in this command will highlight them.

6. Checking the Firewall

Firewalls can block SSH connections even if the server is running. Verify this port 22 is open & accessible:

Using ufw (Uncomplicated Firewall)

For systems using ufw, check the status with:

bash Copy code 
sudo ufw status

Ensure you see a rule allowing SSH:

bash Copy code 
22/tcp ALLOWS Anywhere

If not, allow SSH traffic:

bash Copy code 
sudo ufw allow ssh

Using iptables

For systems using iptables, run:

bash Copy code 
sudo iptables -L -n

Look for a rule permitting traffic on port 22.

7. Verifying Network Connectivity

If the SSH server is running but you can’t connect, ensure the server is reachable over the network. Use ping to test connectivity:

bash Copy code 
ping server-ip

If the server isn’t responding, there might be a network issue.

Conclusion

How to check if ssh server is running on Linux? Ensuring your SSH server is running on Linux involves a combination of checking the service status, verifying listening ports, testing connectivity, and reviewing logs. These steps not only help confirm the server’s functionality but also assist in diagnosing and resolving potential issues. By regularly monitoring and testing your SSH setup, you can maintain secure and reliable access to your Linux systems.

Whether you’re troubleshooting or performing routine checks, the methods outlined in this guide will equip you to confidently manage SSH servers on any Linux distribution.