Essential for Beginners: Methods to Open Ports in Linux Firewall

This article introduces the necessity and common methods for opening ports on Linux servers, helping beginners get started quickly. Opening ports is fundamental for services to communicate externally (e.g., Web on port 80, SSH on port 22); otherwise, connection refusals will occur. Common tools are categorized into three types: UFW is suitable for Ubuntu/Debian with minimal operations, following steps: installation, allowing ports (e.g., `allow 22/tcp`), enabling, and verification; firewalld applies to CentOS/RHEL with zone management, steps: checking status, adding port rules (specify a zone like `public`), reloading, and verification; iptables is a universal underlying tool with powerful functions but complex syntax, requiring adding rules, saving (to avoid loss after restart), and verification. Port openness can be verified using telnet, nc (netcat), or curl. Beginners should note: prefer UFW/firewalld, avoid opening high-risk ports, ensure rules take permanent effect, and confirm the service is running.