Linux Boot Process? Best Geeks Know It!

Nawaz Abbasi — Tue, 06 May 2025 16:00:00 +0000

The Linux boot process is a sequence of events that initializes a Linux system from a powered-off state to a fully operational state. The knowledge of Linux boot process is essential when it comes to technical interviews, but sometimes it becomes difficult to remember or recall the key steps in the process. This article discusses a quick and easy way to remember it - Best Geeks Know It! Yes, you only need to remember that.

Best Geeks Know It -> B – G – K – I -> BIOS – GRUB – KERNEL – INIT

This BGKI acronym provides a high-level overview of the Linux boot process. Each step builds upon the previous one, gradually bringing the system to a fully operational state. Of course, there are more detailed processes within each step, but this simplified version should give you a good foundation for understanding and remembering the Linux boot sequence.

Here's a concise expansion of B-G-K-I:

B - BIOS/UEFI

Performs Power-On Self-Test (POST)
Checks hardware: CPU, RAM, storage
Loads MBR (Master Boot Record) or GPT (GUID Partition Table)
Transfers control to bootloader

G - GRUB

Located in first 512 bytes of boot drive
Reads /boot/grub/grub.conf
Shows menu with kernel options
Loads selected kernel + initramfs (temporary root filesystem) into RAM
Passes boot parameters to kernel
Can handle multiple OS boot options

K - KERNEL

Decompresses itself into RAM
Initializes hardware and drivers
Mounts root filesystem, loads initramfs
Sets up memory management
Starts device detection
Creates kernel threads

I - INIT (systemd in modern systems)

PID 1 (first process)
Reads /etc/inittab (traditional) or unit files (systemd)
Sets default runlevel/target
Starts essential services in order:
- System services
- Network services
- Display manager
- User interface (CLI/GUI)
Reaches default target state

Key files to remember

/boot/grub/grub.conf - GRUB configuration

/etc/systemd/system/ - systemd unit files

/etc/inittab - Init configuration (traditional)

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Linux Boot Process? Best Geeks Know It!