How to check open ports on RHEL 8 / CentOS 8 Linux

Firewalld is a an underlining mechanism for firewall configuration on RHEL 8 / CentOS 8. Current RHEL 8 / CentOS 8 version of the Firewalld daemon is based on Nftables. To check open ports on RHEL 8 / CentOS 8 you can use the firewall-cmd command as shown below. We will also discuss how to check open ports remotely with the nmap command.

In this tutorial you will learn:

• How to check open ports on RHEL 8.
• How to check services on RHEL 8.
• How to check open ports remotely using nmap.
• How to list open ports and service with firewall-cmd.

Check open ports on RHEL 8 Linux firewall using the firewall-cmd command.

Software Requirements and Conventions Used

How to check open ports on RHEL 8 / CentOS 8 Linux step by step instructions

When checking for open firewall ports on RHEL 8 / CentOS 8 Linux it is important to know that firewall ports can be opened in two main different ways. Firstly, the firewall port can be opened as part of a pre-configured service. For example:

# firewall-cmd --zone=public --permanent --add-service=http

Secondly, the ports can be open directly as custom user predefined ports. Example:

# firewall-cmd --permanent --add-port 8080/tcp

1. Check service ports opened:

   # firewall-cmd --list-services
   cockpit dhcpv6-client http https ssh
   

   The above services have their relevant ports open.

2. Check for ports opened:

   # firewall-cmd --list-ports
   20/tcp 8080/tcp
   

   The above ports, namely 20 and 8080 are open for incoming traffic.

3. Check for all open ports and services:

   # firewall-cmd --list-all
   

4. Lastly you can get a precise overview of all open ports by the nmap command for any remote Linux host. For example the below nmap command will probe 1000 most commonly used ports:

   $ nmap rhel8
   Host is up (0.78s latency).
   Not shown: 994 filtered ports
   PORT     STATE  SERVICE
   20/tcp   closed ftp-data
   22/tcp   open   ssh
   80/tcp   open   http
   443/tcp  closed https
   8080/tcp closed http-proxy
   9090/tcp closed zeus-admin
   

   Please note that closed means that the firewall port is open, however, the underlining service on the actual RHEL 8 / CentOS 8 server is not running. It is also possible to check for a specific port. For example:

   $ nmap -p 80 rhel8
   
   PORT   STATE SERVICE
   80/tcp open  http
   

Visit our nmap guide for more nmap command usage examples.