What are the main methods of protecting and securing a Linux server?

The main methods of protecting and securing a Linux server include:

• System and package updates — regularly applying patches and updates to fix vulnerabilities.
• Firewall configuration (e.g., iptables, firewalld) — restricting incoming and outgoing traffic on necessary ports.
• Using SSH with key authentication — disabling passwords and using keys for access.
• Restricting user and group permissions — principle of least privilege, configuring sudo.
• Monitoring and logging — setting up logging systems (e.g., rsyslog), analyzing logs for suspicious activity.
• Using SELinux or AppArmor — an additional access control layer.
• Disabling unnecessary services and daemons — reducing attack surface.
• Configuring fail2ban or similar tools — automatically blocking IPs after suspicious login attempts.

Example of a simple iptables rule to allow only SSH and HTTP:

iptables -P INPUT DROP
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT