In CentOS 7.x, the default firewall is firewalld. Here is an example using CentOS 7.6
1.To check the firewall status, run the command: `sudo firewall-cmd --state`
If the firewall status shows "not running," it means that the firewall is not enabled.
2.To enable the firewall, you can use the following command: `systemctl start firewalld`.
"Running" indicates that the firewall is currently active and running.
3.disable the firewall, you can run the command: `systemctl stop firewalld.service`.
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4.restart the firewall, you can run the command: `systemctl restart firewalld.service`.
5.To view all open ports in the firewall, you can use the command: `firewall-cmd --zone=public --list-ports `.
As shown in the above image, only port 13360 is open, which is the remote port number.
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6.Open port
firewall-cmd --zone=public --add-port=80/tcp --permanent # Open port 80
The return value "success" indicates that the port has been successfully opened.
7.firewall-cmd --reload # Make the configuration take effect immediately.
As shown in the above figure, please check all the open ports of the firewall. Port 80 is currently open.
8.firewall-cmd --zone=public --remove-port=80/tcp --permanent #Close port 80.
9.After closing port 80, check that port 80 is closed once the configuration takes effect.
