Guide to Open And Close Ports on CentOS 6/7

Updated: 28 September 2026 · Applies to: Ubuntu 24.04, Debian 12, AlmaLinux 9 and Rocky Linux 9

CentOS 6 and 7 are end of life. These are the current ways to open and close a port (5555/tcp in the examples).

AlmaLinux / Rocky Linux (firewalld)

firewall-cmd --permanent --add-port=5555/tcp       # open
firewall-cmd --permanent --remove-port=5555/tcp    # close
firewall-cmd --reload
firewall-cmd --list-ports

Ubuntu / Debian (UFW)

ufw allow 5555/tcp            # open
ufw delete allow 5555/tcp     # close
ufw status

Check that the port is open

1. On the server, check that a program listens on the port: ss -tlnp | grep 5555. If nothing listens, the port looks closed even with the firewall open.
2. From another computer, test it: nc -zv SERVER-IP 5555.

Note: On cPanel servers the firewall is usually managed with the firewall tool installed in WHM; open ports there instead of with firewall-cmd.

Tip: On a Ucartz VPS, keep the VNC console open (client area › your VPS service › VPS dashboard) while you change firewall or network settings. If you lock yourself out of SSH, you can still fix it from the console.