Demystifying the Linux Boot Process: A Visual Guide for Seamless Understanding and Troubleshooting.

Linux Boot Process Illustrated. The diagram below shows the steps.

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Collected.

Step 1 —
When we turn on the power, BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface) firmware is loaded from non-volatile memory and executes POST (Power On Self Test).

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Step 2 —
BIOS/UEFI detects the devices connected to the system, including CPU, RAM, and storage.

Step 3 —
Choose a booting device to boot the OS from. This can be the hard drive, the network server, or CD ROM.

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Step 4 —
BIOS/UEFI runs the boot loader (GRUB), which provides a menu to choose the OS or the kernel functions.

Step 5 —
After the kernel is ready, we now switch to the user space. The kernel starts up systemd as the first user-space process, which manages the processes and services, probes all remaining hardware, mounts filesystems, and runs a desktop environment.

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Step 6 —
systemd activates the default. target unit by default when the system boots. Other analysis units are executed as well.

Step 7 —
The system runs a set of startup scripts and configure the environment.

Step 8 —
The users are presented with a login window. The system is now ready.

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