How Linux Boots

This video is an overview of how Linux boots from power on to login. Watch the bonus: video:   • BONUS: How to Watch Linux Kernel Messages ...   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.