Whenever a Linux system is booted, a number of processes are started to initialize the system. This process is known as system startup or initialization, and it typically happens in the following order:
The Basic Input/Output System (BIOS) is the first thing that runs when a computer is turned on. It is responsible for booting the computer by reading the boot sector of the hard drive, which contains the boot loader.
The MBR is a small piece of code that is responsible for loading the boot loader. It is typically located on the first sector of the hard drive.
The boot loader is a program that is responsible for loading the operating system kernel. The most common boot loader used on Linux systems is GRUB (Grand Unified Bootloader).
The kernel is the core of the operating system and is responsible for managing the system's resources, such as memory, devices, and processes.
The init process is the first process that is started by the kernel. It is responsible for starting all other processes on the system.
After the init process has started all other necessary processes, the system is said to be in user space. This is where normal users can login and run programs.