Enable Firewalld
To enable firewalld, run the following command as root:
systemctl enable firewalld
Start Firewalld
To start firewalld, run the following command as root:
systemctl start firewalld
Check the Status of Firewalld
To check the status of firewalld, run the following command as root:
systemctl status firewalld
Open a Port on CentOS/RHEL 7
Starting with CentOS and RHEL 7, firewall rule settings are managed by firewalld service daemon. A command-line client called firewall-cmd can talk to this daemon to update firewall rules permanently.
To open up a new port (e.g., TCP/80) permanently, use these commands.
$ sudo firewall-cmd –zone=public –add-port=80/tcp –permanent
$ sudo firewall-cmd –reload
Without “–permanent” flag, the firewall rule would not persist across reboots.
Check the updated rules with:
$ firewall-cmd –list-all
Open a Port on CentOS/RHEL 6
On CentOS/RHEL 6 or earlier, the iptables service is responsible for maintaining firewall rules.
Use iptables command to open up a new TCP/UDP port in the firewall. To save the updated rule permanently, you need the second command.
$ sudo iptables -I INPUT -p tcp -m tcp –dport 80 -j ACCEPT
$ sudo service iptables save
Another way to open up a port on CentOS/RHEL 6 is to use a terminal-user interface (TUI) firewall client, named system-config-firewall-tui.
$ sudo system-config-firewall-tui
Choose “Customize” button in the middle and press ENTER.
If you are trying to update the firewall for any well-known service (e.g., web server), you can easily enable the firewall for the service here, and close the tool. If you are trying to open up any arbitrary TCP/UDP port, choose “Forward” button and go to a next window.
Add a new rule by choosing “Add” button.
Specify a port (e.g., 80) or port range (e.g., 3000-3030), and protocol (e.g., tcp or udp).
Finally, save the updated configuration, and close the tool. At this point, the firewall will be saved permanently.
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