Firewalld service not works in centos 6, It works only from centos 7 and higher versions
rpm -qa firewalld
sudo apt install firewalld
$ sudo systemctl start firewalld
$ sudo systemctl enable firewalld #enable the service to auto-start at boot time
$ sudo systemctl status firewalld #to know service status
You can also check whether the daemon is running or not, using the firewall-cmd tool as below
$ sudo firewall-cmd –state
If you want to do any changes permanently,You need to reload firewalld. This will reload firewall rules and their settings.
$ sudo firewall-cmd –reload
$ sudo firewall-cmd –zone=public –add-port=80/tcp –permanent
$ sudo firewall-cmd –reload
sudo firewall-cmd –zone=public –remove-port=443/tcp –permanent
$ sudo firewall-cmd –reload
To add service as permanent
$ firewall-cmd –permanent –add-service=https