How to configure firewalld quickly

This article covers the fundamental tasks necessary to configure the firewalld service quickly. I'll assume you already appreciate the importance of a firewall and have a general understanding of how firewalls protect servers and workstations.

These are the steps for configuring this firewall:

1. Check its current status
2. Check its configuration
3. Open a port
4. Close a port
5. Make the settings persistent
6. Reload the firewall configuration

To help you find the information you need, I've organized the article in a How do you? format that addresses these steps. Simply scroll down to your question and find the commands. If you need more detail on managing firewalld, read Shashank Nandishwar Hegde's article An introduction to firewalld rules and scenarios.

How do you check the firewalld status?

First, ensure the firewalld service is installed, started, and enabled:

$ sudo systemctl status firewalld

$ sudo systemctl start firewalld

$ sudo systemctl enable firewalld

Starting a service activates it for the current runtime, whereas enabling a service causes it to start when the system boots.

How do you check the current configuration?

To display the services or ports currently open on the firewall for the public zone, type:

$ sudo firewall-cmd --list-all --zone=public

Notice the zone and the services or ports. The zone is a configuration related to a specific location or server role.

If desired, you can display the open ports by service or port number:

$ sudo firewall-cmd --list-services

$ sudo firewall-cmd --list-ports

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How do you open a port?

If the existing firewall configuration blocks a service you need, open the appropriate port. You can specify it by service name if it's a common service. However, if the service is uncommon, developed in-house, or uses a custom port number, you can open the firewall port by port number. Here are two examples for web services:

$ sudo firewall-cmd --zone=public --add-service=http

$ sudo firewall-cmd --zone=public --add-port=80/tcp

Note the use of /tcp (or /udp, depending on the protocol).

This configuration is non-persistent. As noted below, you'll need the --permanent flag to persist the settings.

Use the --list-services or --list-ports option to verify the settings.

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How do you close a port?

It's also possible that an open port represents a no-longer-installed service on the system or that it should be closed for some other reason. Close ports by service name or port number by using these commands:

$ sudo firewall-cmd --zone=public --remove-service=http

$ sudo firewall-cmd --zone=public --remove-port=80/tcp

Again, with the above commands, this configuration is non-persistent.

How do you make the firewall settings persistent?

The --permanent option makes the firewall changes persist through reboots. You can integrate the flag into the configuration commands:

$ sudo firewall-cmd --permanent --zone=public --add-port=80/tcp

How do you reload the configuration?

Finally, reload the firewall to integrate your changes into the current runtime. Do this as a separate step following the configuration changes:

$ sudo firewall-cmd --reload

One note regarding restart versus reload: Linux reads configuration files during the boot process, so what do you need to do when changing a configuration file? The obvious answer is to reboot the server, causing the system to reread the configuration file and implement the new changes. A reboot is often a bad idea (causing downtime), so you may choose to restart a service (systemctl restart sshd).

However, the problem with restarting a service is that it drops existing connections. In many cases, a better alternative is to reload the service, which rereads the config file but does not drop existing connections, and therefore there is no interruption in service.

Learn more

The importance of a firewall is an established fact. This article provides the basic commands necessary to quickly check the configuration, add or remove rules, and reload the settings. You can check the Red Hat documentation for details on additional configurations, using various zones, port forwarding, and more.