BIOS startup phase: Detailed explanation of the Linux system startup process

BIOS startup phase: Detailed explanation of the Linux system startup process

1. BIOS phase

BIOS (Basic Input/Output System) is a basic software in the computer system and is responsible for Perform hardware self-test and initialization when the computer starts. When the computer is turned on, the BIOS will first be activated and loaded into memory for execution. At this stage, the BIOS will perform the following steps:

1.1 POST (Power-On Self-Test) self-test

After the computer is turned on, the BIOS will perform a POST self-test to check the computer Whether the basic functions of the hardware are normal, such as CPU, memory, hard disk, graphics card and other hardware devices. If there is a hardware failure, the BIOS will beep or display an error message on the monitor.

1.2 Initialize and load the boot device

After self-test, the BIOS will find the boot device (usually the hard disk) in the CMOS and load the boot sector on the device into memory for execution. The boot sector contains the bootloader, which is responsible for loading the operating system.

1.3 Start the boot loader

The BIOS will load the bootloader into memory for execution. In Linux systems, commonly used boot loaders include GRUB (GRand Unified Bootloader) or LILO (LInux LOader). These bootloaders display a boot menu and guide the user in selecting which kernel to boot.

2. Boot loader stage

The bootloader (bootloader) is responsible for loading the operating system kernel and initializing the RAM disk image (initrd), and passing control to the operating system Kernel. At this stage, the boot loader will perform the following operations:

2.1 Load the kernel

The boot loader will load the operating system kernel (vmlinuz) into memory for execution. The kernel is the core of the operating system and is responsible for managing system resources, process scheduling, device drivers and other functions.

2.2 Initialize RAM disk image

The RAM disk image (initrd) is a temporary root file system used to load necessary drivers and file system modules before the operating system starts normally. The bootloader loads the initrd into memory and starts it together with the kernel.

2.3 Pass control to the kernel

The boot loader will pass control to the operating system kernel, allowing the kernel to continue the system initialization process. The kernel will parse the initrd, load necessary modules and drivers, start user space programs, etc.

3. Linux kernel startup phase

The Linux kernel startup process can be divided into the following stages:

3.1 Startup parameter analysis

When the kernel starts, it will parse the startup parameters passed by the boot loader, including the root file system, startup level, etc. These parameters tell the kernel how to initialize the system.

3.2 Initialization process and memory management

The kernel will initialize the first process in the system (init process) and the memory management subsystem. The memory management subsystem is responsible for managing the physical memory and virtual memory in the system and allocating memory to processes.

3.3 Initializing device drivers

The kernel will initialize various hardware device drivers in the system, including network cards, disks, USB and other devices. These drivers are responsible for communicating with the hardware device so that the operating system can use the hardware device normally.

3.4 Mount the root file system

The kernel will mount the root file system and set the root directory of the file system to the system root directory for user space programs to access. Usually the root file system is located on the partition of the hard disk, which can be a file system format such as ext4, xfs, etc.

3.5 Start user space programs

The kernel will start user space programs, including init system processes and other system services. These user space programs are responsible for the daily operation of the system, providing functions such as user interface and application scheduling.

Through the above steps, the Linux system has completed the startup process from the BIOS stage to the kernel startup stage. In actual applications, you can use debugging tools and logs to learn more about each stage of the system startup process. I hope this document will help you understand the Linux system startup process.

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