How Linux Boots

This video is an overview of how Linux boots from power on to login.
Watch the bonus: video:https://youtu.be/4yDxxodO5vI

HOW LINUX BOOTS

A simplified view of the boot process:

1. POST (Power On Self Test) – Runs diagnostics on hardware.

2. BIOS (Basic Input Output System) or UEFI (Unified Extensible Firmware
Interface) – Finds and starts the boot loader.

3. GRUB (Grand Unified Boot Loader) – Gives users a chance to choose an OS
(Operating System) to run and also offers older kernels, recovery
mode, memory testing and a shell. GRUB usually loads the latest Linux
kernel and intramfs automatically. It starts the kernel and exits.

4. Linux Kernel – Initializes devices and loads drivers, kernel modules and
the init program from initramfs. It then mounts the root filesystem and
starts init with a process ID of 1. This is where user space begins.

5. Systemd – The init program found on most modern Linux distribution. It
starts and manages essential services such as udevd and syslogd. It sets up
network configuration and starts high level services like cron and cups.
Once the services are running, it then starts getty for user login or a
graphic desktop manager like GDM, KDM or LightDM. the init program is also
used to perform an orderly computer shutdown.