boot

View the boot process documentation

$ man 7 boot

$ man 7 bootup

This is a documentation page describing the Linux boot sequence, not an executable command.

The boot(7) man page documents the Linux system startup process based on UNIX System V Release 4. The boot sequence consists of several phases:
Hardware Boot (BIOS/UEFI)

POST (Power-On Self-Test) runs, hardware is initialized, and firmware locates the bootloader

The bootloader locates and loads the kernel into memory

The kernel initializes devices, starts the swapper process (kswapd), and mounts the root filesystem

The first userspace process (PID 1) starts. Modern systems use systemd, older systems use SysVinit

System services are started according to the configured runlevel or systemd target

This documentation primarily describes the traditional SysV init boot process. Most modern Linux distributions use systemd, which has a different boot architecture documented in bootup(7).
The exact boot sequence varies between distributions, hardware platforms, and init systems in use.

The System V init process originated in AT&T Unix System V released in 1983. Linux distributions historically adopted this model before the transition to systemd beginning around 2010-2011. Systemd became the default init system in most major distributions by 2015.

systemctl(1), journalctl(1), grub(8)