Boot Loader loading phase: Linux system startup sequence analysis

Boot Loader loading phase: Linux system startup sequence analysis

When the Linux system starts, the Boot Loader (boot program) plays a vital role. It is responsible for the loading and initialization of the boot system kernel. The first program during system startup. This article will introduce the loading phase of Boot Loader and the startup sequence of the Linux system, and analyze the entire startup process through specific code examples.

1. Boot Loader loading phase

The Boot Loader loading phase usually includes the following steps:

1. BIOS/UEFI initialization: When the computer is turned on, the BIOS ( Basic Input Output System) or UEFI (Unified Extensible Firmware Interface) will start to initialize and self-test the hardware.
2. Boot Loader loading: BIOS/UEFI will load the Boot Loader in the boot sector of the boot device. The most common Boot Loader is Grub (Grand Unified Bootloader).
3. Boot Loader initialization: Boot Loader is responsible for loading the operating system kernel and initializing the system environment, and then transfers control to the kernel.

2. Linux system startup sequence

After the Boot Loader is loaded, the Linux system startup sequence usually includes the following stages:

1. Boot Loader stage: Boot Loader is responsible for loading the kernel image file (vmlinuz) and initializing the RAM disk image (initrd.img).
2. Kernel startup phase: After the kernel is loaded, the basic components and drivers of the system will be initialized, and memory management and process scheduling mechanisms will be established.
3. User space initialization phase: After the kernel loading is completed, init, the first process in user space, is started, and then system services and user space programs are loaded.
4. System initialization phase: After the initialization of system services and user space programs is completed, the system enters normal operation.

3. Code sample analysis

The following is the sample code of the Boot Loader (Grub) configuration file (/boot/grub/grub.cfg):

set default="0"
set timeout=5
menuentry "Linux" {
    set root=(hd0,1)
    linux /vmlinuz root=/dev/sda1 ro
    initrd /initrd.img
}

In this code, the default options and timeout are first set, then a menu item named "Linux" is defined, the kernel file path and the initialization RAM disk file path are specified, and finally the kernel startup parameters are specified.

Through the above sample code, we can understand the configuration process of the Boot Loader loading phase and how to start the Linux system kernel through the Boot Loader.

Summary: The Boot Loader loading phase is a crucial link in the Linux system startup process. It is responsible for loading the kernel and passing startup parameters, laying the foundation for the normal operation of the system. By understanding the loading sequence and configuration method of Boot Loader, you can better grasp the startup process of the Linux system.

The above is the analysis of the Boot Loader loading phase and the Linux system startup sequence. I hope it will be helpful to you!

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