The UNIX boot process describes how the system starts from the moment the computer powers on until the login prompt appears.

The sequence typically follows:

Power ON → Firmware (BIOS/UEFI) → Bootloader → Kernel → init/systemd → Services → Login

Let’s break it down.

1️⃣ Power On & Hardware Initialization (BIOS/UEFI)

When the system is powered on:

• BIOS/UEFI performs a hardware test known as POST (Power-On Self-Test).

• Checks CPU, memory, disks, keyboard, etc.

• Then it looks for a bootable device (HDD, SSD, USB, PXE).