How to Change the SSH Port in Linux

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How to Change the SSH Port in Linux

By default, SSH listens on port 22. Changing the default SSH port adds an extra layer of security to your server by reducing the risk of automated attacks.

This tutorial explains how to change the default SSH port in Linux. We will also show you how to configure your firewall to allow access to the new SSH port.

The best way to protect your server from attacks is to configure your firewall to allow access to port 22 only from trusted hosts and set up an SSH key-based authentication .

Changing the SSH Port

Changing the SSH port of an image is a simple task. All you need to do is to edit the SSH configuration file and restart the service.

The following sections explain how to change the SSH Port on a Linux system.

1. Choosing a New Port Number

In Linux, port numbers below 1024 are reserved for well-known services and can only be bound to by root. Although you can use a port within a 1-1024 range for the SSH service to avoid issues with port allocation in the future, it is recommended to choose a port above 1024.

In this example will change the SSH port to 5522, you can choose any port you want.

2. Adjusting Firewall

Before changing the SSH port, you’ll need to adjust your firewall to allow traffic on the new SSH port.

If you are using UFW, the default firewall configuration tool for Ubuntu, run the following command to open the new SSH port:

sudo ufw allow 5522/tcp

In CentOS, the default firewall management tool is FirewallD. To open the new port run:

sudo firewall-cmd --permanent --zone=public --add-port=5522/tcpsudo firewall-cmd --reload

CentOS users also need to adjust the SELinux rules:

sudo semanage port -a -t ssh_port_t -p tcp 5522

If you are using iptables as your firewall, to open the new port, run:

sudo iptables -A INPUT -p tcp --dport 5522 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT

3. Configuring SSH

Open the SSH configuration file /etc/ssh/sshd_config with your text editor:

sudo vim /etc/ssh/sshd_config

Search for the line starting with Port 22. In most cases, this line starts with a hash (#) character. Remove the hash # and enter the new SSH port number:

/etc/ssh/sshd_config
Port 5522

Be extra careful when modifying the SSH configuration file. The incorrect configuration may cause the SSH service to fail to start.

Once done, save the file and restart the SSH service to apply the changes:

sudo systemctl restart ssh

In CentOS the ssh service is named sshd:

sudo systemctl restart sshd

To verify that SSH daemon is listening on the new port 5522, type:

ss -an | grep 5522

The output should look something like this:

tcp   LISTEN      0        128            0.0.0.0:5522           0.0.0.0:*
tcp   ESTAB       0        0      192.168.121.108:5522     192.168.121.1:57638
tcp   LISTEN      0        128               [::]:5522              [::]:*

Using the New SSH Port

To specify the port, invoke the ssh command followed by the -p <port_number> option:

ssh -p 5522 username@remote_host_or_ip

If you are regularly connecting to multiple systems, you can simplify your workflow by defining all of your connections in the SSH config file .

Conclusion

In this tutorial, you have learned how to change the SSH port on a Linux server. You should also set up an SSH key-based authentication and connect to your Linux servers without entering a password.

Feel free to leave a comment if you have any questions.

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