Phase 2: Boot & Init
Every time you press the power button, a carefully orchestrated sequence runs — from the firmware waking up the CPU to the login prompt appearing. Understanding this sequence is fundamental to debugging startup failures, customizing boot behavior, and understanding how systemd controls your system.
What You'll Learn
1. Linux Boot Process
Step-by-step: power on → BIOS → GRUB → kernel → PID 1 → login.
Intermediate2. GRUB Bootloader
How GRUB finds and loads the kernel, config format, kernel parameters.
Intermediate3. Kernel Startup
What the kernel does before PID 1: hardware detection, memory setup.
Intermediate4. initramfs
Why a temporary RAM filesystem is needed before mounting root.
Intermediate5. systemd vs init
Architecture comparison: sequential SysV scripts vs parallel systemd.
Intermediate6. systemd Units
Service, target, socket, timer units — anatomy and practical usage.
Intermediate7. Boot Targets & Runlevels
systemd targets vs SysV runlevels, rescue and emergency modes.
Intermediate8. journald
Binary logging, journalctl usage, log levels, persistence settings.
IntermediateFrequently Asked Questions
What will I learn here?
This page covers the core concepts and techniques you need to understand the topic and progress confidently to the next lesson.
How should I use this page?
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