How to Close a Specific Port on Linux

On a Linux system, closing a particular port might help increase security or free up system resources. This short tutorial will walk you through closing a port using IPtables, FirewallD, UFW, or stopping the service. If you are looking for a tutorial to open a port in Linux, please check our tutorial: How to Open a Specific Port on Linux

How to Check Open Ports on Linux

First, let’s see which ports are open. You can use one of these commands:

Using netstat:

sudo netstat -tuln

Below is a sample output in which underlined in red are the ports which are opened. (22 and 53)

Using ss:

sudo ss -tuln

Below is a sample output in which underlined in red are the ports which are opened. (22 and 53)

Using lsof:

The lsof command is mostly not preinstalled on Linux systems. You need to manually install this command to use. If you are using a Debian-based system like Ubuntu, use the command: sudo apt-get install lsof to install. For Centos/Redhat: sudo yum install lsof and for Fedora: sudo dnf install lsof

sudo lsof -i -P -n

Below is a sample output in which underlined in red are the ports which are opened. (22 and 53)

These commands will list all the open ports on your system.

How to Close a Port Using UFW (Uncomplicated Firewall)

For Ubuntu and other Debian-based systems, UFW is a straightforward firewall management application.

Install UFW (if it’s not installed):

sudo apt-get install ufw
sudo ufw enable

Close the Port:

Replace <port_number> with the port number, you want to close.

sudo ufw deny <port_number>

Example screenshot:

Check UFW Status:

sudo ufw status

How to Close a Port Using iptables

A more sophisticated tool for controlling firewall rules is IPtables. To install IPtables use the command: sudo apt-get install iptables if it was not installed.

Block the Port:

Replace <port_number> with the port number, you want to close.

sudo iptables -A INPUT -p tcp --dport <port_number> -j DROP
sudo iptables -A INPUT -p udp --dport <port_number> -j DROP

Example screenshot:

Save IPtables Rules:

On Debian-based systems:

sudo sh -c "iptables-save > /etc/iptables/rules.v4"

On Red Hat-based systems:

sudo service iptables save

How to Close a Port Using Firewalld

Firewalld is the default firewall tool for CentOS and Fedora.

Install Firewalld (if it’s not installed):

sudo yum install firewalld

Block the Port:

Replace <port_number> with the port number, you want to close.

sudo firewall-cmd --permanent --remove-port=<port_number>/tcp
sudo firewall-cmd --permanent --remove-port=<port_number>/udp

Example screenshot:

Reload Firewalld:

sudo firewall-cmd --reload

Check Firewalld Status:

sudo firewall-cmd --list-all

How to Stop a Service to Close a Port

Sometimes, a port is open because a service is using it. Stopping the service will close the port. In that case, blocking the service will be the best option rather than closing the port.

Identify the Service:

Use netstat, ss, or lsof to find which service is using the port.

sudo netstat -tuln | grep <port_number>

OR

sudo ss -tuln | grep <port_number>

OR

sudo lsof -i :<port_number>

For Example:

Replace <port_number> with the actual port number.

Stop the Service:

Replace <service_name> with the name of the service.

sudo systemctl stop <service_name>

For example:

Disable the Service (if needed):

This prevents the service from starting at boot.

sudo systemctl disable <service_name>

On Linux, there are multiple methods to close a port: UFW, IPtables, Firewalld, or terminating a service. Select the approach that best suits your needs. For simplicity, UFW is a great choice. For more control, IPtables is ideal. Firewalld is perfect for Red Hat-based distributions, and stopping a service directly is effective when dealing with a specific application. Always ensure you correctly identify the service using the port before stopping it.