How do I open port 80 (Apache Web Server) under Red Hat / CentOS / Fedora Linux?

Answer

The default configuration file for iptables based firewall under RHEL / CentOS / Fedora Linux is /etc/sysconfig/iptables. Open this file using a text editor such as vi:
Linux Open Port 80 (http)

# vi /etc/sysconfig/iptables
Append rule as follows:
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
Save and close the file. Restart iptables:
# /etc/init.d/iptables restart