This post will show you how to open a firewall port of a Linux CentOS server using the command line.
Firewall-Cmd
In CentOS, the firewall is managed by the firewall-cmd command that control which port is open or blocked between the defined network zones. In most systems, you will probably have a single zone (public).
The firewall-cmd command is the client of the firewall daemon that handles the firewall.
Check Zone
Now that we know a bit about the firewall daemon, let us first check which zone is active on our systems by running the following command.
firewall-cmd --get-active-zones
My output is shown below and with no surprise, I only have a public zone which I will take note of and use to open a port.
[[email protected] ~]# firewall-cmd --get-active-zones
public
interfaces: ens3
Open Port
To open a port, I will run the following commmand.
firewall-cmd --zone=public --add-port=3100/tcp --permanent
After opening the port, we need to reload the daemon to apply the changes.
firewall-cmd --reload
At this stage the change is completed and the port is open.
To read more about the firewall-cmd command run.
man firewall-cmd