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On CentOS 7, firewall-cmd is used to maintain the firewall.
List All Rules
firewall-cmd --list-allAllow a port
This example allows a TCP port through the firewall, for all network interfaces in the "public" zone:
firewall-cmd --zone=public --add-port=3306/tcp --permanentThis example allows a UDP port through the firewall, for all network interfaces in the "public" zone:
firewall-cmd --zone=public --add-port=20202/udp --permanentReload the firewall
firewall-cmd --reload
Delete a rule
firewall-cmd --zone=public --remove-port=3306/tcp