Change the SSH Port in the Linux Ubuntu operating system

Changing the SSH (Secure Shell) port in the Linux Ubuntu operating system is a fundamental yet crucial step for enhancing the security of your server. By default, SSH attends port 22. Many automated attacks target this default port, making it a common vulnerability. Changing the port to a non-standard one can significantly reduce the risk of these attacks. 

Here's a comprehensive guide to Ubuntu change SSH port.

Prerequisites

Before proceeding, ensure you have:

1. Access to a user account with sudo privileges.

2. Understanding of command-line operations.

Step 1: Backup the SSH Configuration File

First, it's always good practice to back up your SSH configuration file if something goes wrong. You can do this by running:

sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak

It creates a copy of the existing SSH configuration file.

Step 2: Edit the SSH Configuration File

Next, open the SSH configuration file in a text editor. Commonly used text editors in Ubuntu are `nano`, `vi`, or `vim`. For simplicity, we'll use `nano`:

sudo nano /etc/ssh/sshd_config

Step 3: Change the SSH Port

Look for the line that specifies the port in the SSH configuration file. By default, it looks like this:

#Port 22

Uncomment this line and remove the `#` Change `22` to your desired port number.

Step 4: Save and Exit the Editor

After making the changes, save the file.

Exit the editor. 

In `nano`, you can press `CTRL + X`

Enter `Y` to confirm the changes.

`Enter` to save.

Step 5: Adjust the Firewall Settings

You need to update your firewall rules to allow the new SSH port through the firewall. If you are using `ufw`, the commands are:

sudo ufw allow 2222/tcp

sudo ufw delete allow 22/tcp

Replace `2222` with the port number you chose. The first command allows traffic on the new port, and the second command removes the rule for the old port.

Step 6: Restart the SSH Service

For the changes to take effect, you must restart the SSH service with:

sudo systemctl restart ssh

Alternatively, you can use:

sudo service ssh restart

Step 7: Verify the Changes

To ensure that SSH is now listening on the new port, you can use the `ss` or `netstat` command:

sudo ss -tuln | grep 2222

Or, if `ss` is not available:

sudo netstat -tuln | grep 2222

You should see a line indicating SSH listening on the new port.

Step 8: Update SSH Client Configurations (Optional)

If you frequently connect to this server using an SSH client, you should update your client configuration to use the new port by default. You can do this by modifying your local `~/.ssh/config` file to include:

Host yourserver

    HostName yourserver.com

    Port 2222

    User yourusername

It allows you to connect to your server without specifying the port every time.

To Sum it Up!

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