$sudo service firewalld start
$sudo
firewall-cmd --list-all
$sudo
firewall-cmd --get-zones
$sudo
sudo firewall-cmd --zone=home --list-all
$sudo
firewall-cmd --get-default-zone
$sudo
firewall-cmd --get-active-zones
$sudo firewall-cmd --add-port=8081/tcp --permanent
$sudo firewall-cmd --add-port=8081/udp --permanent
$sudo firewall-cmd --reload #important in Fedora 23 (VPS)
References:
[1] firewall-cmd https://docs.fedoraproject.org/en-US/Fedora/19/html/Security_Guide/sec-Open_Ports_in_the_firewall-CLI.html
[2] other firewall-cmd https://www.hiroom2.com/2017/07/12/fedora-26-firewalld-en/
[3] zones https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-using-firewalld-on-centos-7