18.09.2024
2 min
1243
A comprehensive guide to securing a GNU/Linux server, covering SSH configuration, network security, system auditing, high-risk configurations, and additional security recommendations. The article includes clear explanations of each section, illustrations, and direct links to the corresponding GitHub resources.
The SSH Server section is one of the most comprehensive parts of the guide and is entirely dedicated to securely configuring remote access to a GNU/Linux server. It provides step-by-step instructions on which settings should be changed immediately after installation to significantly reduce the risk of unauthorized access.
In this section, you will learn how to replace password-based authentication with more secure SSH keys, disable root login, restrict access to specific users or groups, configure multi-factor authentication (MFA/2FA), and disable outdated encryption algorithms and other insecure settings. It also explains how to properly edit the sshd_config file, what each key parameter does, and which recommended values help strengthen your server’s security.
In addition, the guide provides practical recommendations for protecting SSH against automated attacks, configuring session timeouts, limiting login attempts, verifying the configuration before restarting the service, and addressing other important details that are often overlooked. Nearly every step includes example commands and explanations of why a particular configuration is considered more secure. As a result, this section serves as a complete checklist for securely configuring an SSH server on virtually any modern GNU/Linux system.
The Network section explains in detail how to properly secure the networking layer of a GNU/Linux server, as it is the primary target for most intrusion attempts. Designed as a step-by-step guide, it helps you configure your server so that only essential services are accessible while minimizing unnecessary network-related security risks.
In this section, you will find detailed instructions for configuring UFW (Uncomplicated Firewall), one of the most widely used firewalls for GNU/Linux. It explains how to create firewall rules, open only the required ports, block unwanted connections, and verify that the server is accessible only through the services you intend to expose. The guide also covers PSAD, which analyzes iptables logs to detect port scans, network attacks, and other suspicious activity.
A separate part is dedicated to Fail2Ban and CrowdSec. It provides step-by-step instructions on how these tools work, how they automatically block IP addresses after repeated failed login attempts, and how they protect servers against brute-force attacks. In addition to installation and configuration, the guide explains the underlying principles of each tool, includes practical configuration examples, and offers recommendations for real-world deployments. As a result, this section serves as a ready-to-use checklist for building a solid baseline of network security on a GNU/Linux server.
The Auditing section focuses on assessing the security of a GNU/Linux server after it has been configured. It explains that even a well-secured server should be audited regularly, as new vulnerabilities, configuration errors, and suspicious activity can emerge at any time. To help with this, the section brings together a collection of tools designed to identify security issues early and maintain the overall security posture of the system.
The guide provides a detailed overview of Lynis, one of the most widely used security auditing tools for GNU/Linux. It explains how to run a security audit, interpret the results correctly, and identify weaknesses in the server’s configuration. It also covers AIDE (Advanced Intrusion Detection Environment), which helps monitor the integrity of system files and quickly detect any unauthorized changes. In addition, you will learn how to use Rkhunter and Chkrootkit to detect rootkits, and ClamAV to scan the server for malware.
Special attention is given to analyzing system logs with Logwatch, checking open network ports and running services, and continuously monitoring changes that may indicate a server compromise. The guide explains how to use each tool, when it should be executed, and how to interpret its results effectively. As a result, this section can be used as a comprehensive checklist for performing regular security audits on a GNU/Linux server.
The Danger Zone section focuses on advanced security measures that go beyond the basic configuration of a GNU/Linux server. It covers settings that can significantly strengthen the overall security of the system but also require careful implementation. For this reason, each step is accompanied by detailed explanations so administrators understand how every mechanism works and what impact these changes may have on the system.
In this section, you will find a dedicated guide to Linux kernel hardening using sysctl parameters. It explains which settings help protect against common network attacks, restrict potentially dangerous kernel features, and make the system more resilient to vulnerability exploitation. The guide also covers configuring umask, which defines the default permissions for newly created files and directories, as well as protecting the GRUB bootloader with a password to prevent unauthorized changes to the operating system’s boot parameters.
In addition, the section highlights several important security recommendations that are often overlooked, even by experienced administrators. Each recommendation is accompanied by example commands, explanations of the underlying concepts, and guidance on safe implementation. As a result, this section serves as a valuable complement to the core security configuration and helps strengthen a GNU/Linux server against less obvious but potentially serious threats.
The Miscellaneous section brings together additional recommendations and useful configurations that do not fit into the previous categories but help make a GNU/Linux server both more secure and easier to administer. It includes a collection of practical tips that are commonly applied as the final step after configuring SSH, network security, and performing a security audit.
In this section, you will learn how to configure msmtp, Gmail SMTP, or Exim4 to send system notifications from your server, allowing you to receive timely alerts about errors, updates, and other important events. The guide also explains how to redirect iptables logs to a dedicated log file, making it much easier to analyze network activity and investigate suspicious events. Each topic is accompanied by practical command examples and clear explanations, making the material accessible even to users with limited Linux administration experience.
In addition to the practical tutorials, the final part of the section includes a collection of useful resources and supplementary materials for those who want to explore Linux server security in greater depth. This makes the Miscellaneous section a fitting conclusion to the guide, bringing together helpful tips, additional tools, and valuable references for further learning about GNU/Linux security.
