How to Unfilter a Port in Ubuntu

Internet and network programs on Ubuntu machines use ports to communicate with each other. Each port is dedicated to a specific service. For example, you'll find Telnet connections running on port 23, FTP connections running on port 21 and DNS services running on port 53, among others. Firewall programs running on Ubuntu Linux, such as ufw, can block or filter these ports. With a few simple commands, you can unfilter a port on Ubuntu through a terminal window.

Instructions

1. Start a terminal window on your Ubuntu machine. If you are running the Gnome desktop environment, which is installed by default, you can start a session by going to "Applications," then "Accessories," followed by "Terminal."

2. Determine the port number that you wish to unfilter. Each network service running on Ubuntu has a port number. For example, the http (web) service runs on port 80.

3. Type the following at the command prompt, where XX is the number of the port that you wish to unfilter:

   sudo ufw allow XX

References

• Ubuntu: Firewall Configuration
• Ubuntu: Official Site
• Ubuntu: Starting a Gnome Terminal
• MySQL-Apache-PHP: Linux Port Numbers