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 it and switch to the 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)