In Oracle Linux 9, the firewall service, firewalld, is enabled by default. The service is controlled by the systemctl command.

To start the service:

sudo systemctl unmask firewalld

sudo systemctl start firewalld

To ensure that the service starts automatically when the system starts, run the following command after starting the firewall:

sudo systemctl enable firewalld

To stop the firewall service and prevent it from automatically starting when the system starts, run the following command:

sudo systemctl stop firewalld

sudo systemctl disable firewalld

To prevent the firewall service from being started by other services or through the firewalld D-Bus interface, run the following command after disabling the firewall:

sudo systemctl mask firewalld

To display the current status of the firewall service:

sudo systemctl status firewalld

firewalld.service - firewalld - dynamic firewall daemon
     Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
     Active: active (running) since Thu 2022-05-05 08:41:36 GMT; 5 days ago
       Docs: man:firewalld(1)
   Main PID: 1155 (firewalld)
      Tasks: 4 (limit: 93659)
     Memory: 32.5M
        CPU: 1.438s
     CGroup: /system.slice/firewalld.service
        └─1155 /usr/bin/python3 -s /usr/sbin/firewalld --nofork --nopid