Systemd

Executive Summary Linux boot is a multi-stage handoff: UEFI → Bootloader → Kernel → systemd → Targets → Units. Each stage has failure points. This guide shows the sequence, where failures occur, and how to capture logs. Why understanding boot flow matters: When a Linux server won’t boot, you need to know WHICH stage failed to fix it effectively. A black screen could mean anything from bad hardware to a typo in /etc/fstab. …

Executive Summary Linux is a layered system: from firmware through kernel subsystems to containerized applications. Understanding these layers—and their interdependencies—is critical for reliable, secure, performant infrastructure. This guide covers: Layered architecture (firmware → kernel → userspace → containers) Core subsystems: process scheduling, memory, filesystems, networking systemd: unit management and service lifecycle Production best practices: security, reliability, performance, observability Note: For detailed boot flow and debugging, see the Linux Boot Flow & Debugging guide. …

Executive Summary A security baseline is the foundation: OS-hardened, patched, with restricted access and audit trails. This guide covers minimal-install servers with hardened SSH, firewall (default-deny), LSM enforcement, least-privilege sudo, audit logging, and systemd hardening. Goal: Reduce attack surface, detect breaches, and enforce privilege boundaries. 1. Minimal Install & Patching Minimal Install What it is: Install only required packages (base + SSH + monitoring agent) No GUI, X11, unnecessary daemons Reduces vulnerabilities (fewer packages = fewer CVEs) Install steps (Ubuntu/Debian): …