The process of booting Linux in a BIOS environment involves several critical steps that ensure the operating system is loaded correctly.Initially, when the computer is powered on, the BIOS (Basic Input/Output System) performs a Power-On Self Test (POST) to check the hardware components for any issues. This includes verifying the integrity of the RAM, detecting connected devices, and ensuring that the CPU is functioning properly.Once the POST is successfully completed, the BIOS locates the bootable device, which could be a hard drive, SSD, or USB drive, and reads the Master Boot Record (MBR) or GUID Partition Table (GPT) to identify the bootloader.
The bootloader, typically GRUB (Grand Unified Bootloader) in many Linux distributions, is then executed. This program is responsible for loading the Linux kernel into memory. The bootloader presents a menu to the user, allowing them to select which operating system or kernel version to boot if multiple options are available. After the user makes a selection, the bootloader loads the specified kernel and initial RAM disk (initrd) into memory, preparing the system for the next phase of the boot process.The kernel is then initialized, and it begins to set up the system environment, including detecting hardware components and mounting the root filesystem.
Once the kernel has completed its initialization, it hands over control to the init system, which is the first user-space program to run. In modern Linux distributions, this is often systemd, which takes charge of starting all other services and processes necessary for the operating system to function. The init system reads its configuration files to determine which services to start, managing dependencies and ensuring that everything is in place for the user to interact with the system.
This entire sequence, from BIOS to the fully operational Linux environment, is crucial for the proper functioning of the operating system and highlights the intricate relationship between hardware and software during the boot process.
