$ show imthenachoman/How-To-Secure-A-Linux-Server
This repository is a documentation/runbook, not a software application. It teaches how to secure a Linux server through a long, well-organized markdown guide aimed primarily at Debian-based systems. The content covers SSH key authentication and sshd_config hardening, PAM-based 2FA/MFA and password quality, UFW firewall configuration including Docker interactions, intrusion detection/prevention with fail2ban, CrowdSec, and PSAD, and auditing tools such as AIDE, ClamAV, rkhunter, chkrootkit, logwatch, Lynis, and OSSEC. It also includes a separate kernel sysctl hardening reference table and a short nginx security headers guide. In production, the repository itself does not run anything; its value is the curated collection of copy-paste-ready shell commands, configuration snippets, and operational guidance that a human administrator applies to a server. The architecture is a set of static markdown files with a consistent section pattern (Why, How It Works, Goals, Steps, References), backup-before-edit conventions, and validation steps after changes. The main README is effectively an evolving security runbook with a detailed table of contents, while the auxiliary markdown files serve as standalone reference assets. Recent updates show active maintenance: the guide has been revised for Debian 13 systemd-timesyncd, OpenSSH 9.1 RSA size enforcement, Docker and UFW bypass caveats, and CrowdSec installation. However, some older recommendations remain dated—for example, certain sysctl keys in the hardening table are obsolete or no longer present in modern kernels, and several linked references are from 2018-2019. Because this is a documentation repository rather than executable code, quality assessment focuses on information architecture, practical utility, and reusability rather than software engineering structure.
The LLM identified 3 files worth highlighting for reuse:
A curated, self-contained table of Linux kernel sysctl keys with recommended secure values and links to kernel documentation. It synthesizes recommendations from multiple security sources and can be lifted directly into another hardening guide, sysctl configuration baseline, or Ansible/Chef hardening role. The cautious disclaimer and documentation links demonstrate good research hygiene.
The primary deliverable: a comprehensive, structured runbook for securing a Linux server. Its repeatable section format (Why / How It Works / Goals / Steps / References), emphasis on taking backups before edits, and validation commands after configuration changes make it a reusable template for operations documentation and a practical knowledge base for SSH, UFW, PAM, fail2ban, CrowdSec, AIDE, and related hardening topics.
A concise, standalone set of nginx security header directives including Content-Security-Policy, X-Frame-Options, X-Content-Type-Options, Referrer-Policy, and Permissions-Policy, each linked to authoritative documentation. This file is easily extracted into any nginx configuration or security checklist and demonstrates a clean minimal-reference pattern.