Linux Boot Process Diagram

flowchart TD
   A[Power On
Hardware Initialization] --> B[BIOS/UEFI
Firmware Init
- Hardware checks
- Find boot device]
   B --> C[Boot Loader
GRUB/LILO/etc
- Load kernel
- Load initrd]
   C --> D[Kernel Loading
- Decompress
- Initialize
- Hardware detect]
   D --> E[initrd/initramfs
- Temporary rootfs
- Load drivers
- Mount real root]
   E --> F[Real Root FS
Mount
- Switch to real
filesystem]
   F --> G[Init System
systemd/SysV
- Start services
- User processes]
   G --> H[Login Prompt
User Space
- Desktop/Shell
- Applications]

   style A fill:#ff9999
   style B fill:#ffcc99
   style C fill:#ffff99
   style D fill:#ccff99
   style E fill:#99ffcc
   style F fill:#99ccff
   style G fill:#cc99ff
   style H fill:#ff99cc

Boot Process Steps Explained

1. Power On - Hardware initialization, CPU starts
2. BIOS/UEFI - Firmware tests hardware, locates boot device
3. Boot Loader - GRUB loads kernel and initial ramdisk into memory
4. Kernel - Decompresses, initializes, detects hardware, starts init
5. initrd/initramfs - Temporary filesystem loads essential drivers
6. Real Root - Mounts actual root filesystem, switches from initrd
7. Init System - Starts system services and daemons
8. User Space - Login manager, desktop environment, user applications

Key Files/Locations: - /boot/vmlinuz* - Kernel image - /boot/initrd* - Initial ramdisk - /boot/grub/ - GRUB configuration - /etc/fstab - Filesystem mount points - /sbin/init - First user process (PID 1)