An in-depth discussion of the functions and principles of Linux MBR

During the boot process of the Linux system, Master Boot Record (MBR) plays a vital role. The MBR is the first sector of the hard disk, usually 512 bytes, and contains key information needed to boot the operating system. This article will deeply explore the functions and principles of Linux MBR, and provide specific code examples to help readers better understand.

The function and structure of MBR

The role of MBR mainly includes the following aspects:

1. Boot loader: MBR contains boot loading Boot Loader is responsible for loading the operating system when the computer starts. Common boot loaders include GRUB and LILO.
2. Partition Table: MBR also contains the partition table of the hard disk (Partition Table), which records the starting position, size, partition type and other information of each partition on the hard disk.
3. Signature information: The last two bytes of MBR are AA55H (0x55AA), which is a special identifier used to indicate that the MBR is valid. If these two bytes are not AA55H, the computer will not boot properly.

The MBR structure is as follows:

• The first 446 bytes are the boot loader code, responsible for loading the operating system;
• The next 64 bytes are partitions Table, each partition table entry occupies 16 bytes, and generally supports up to four primary partitions;
• The last two bytes are the AA55H logo.

Linux MBR loading process

During the Linux system boot process, the MBR loading process is as follows:

1. BIOS (Basic Input/Output System) startup: After the computer is powered on, the MBR is first loaded by the BIOS. The BIOS will hand over control to the boot loader in the MBR.
2. Boot loader loads the kernel: The boot loader loads the operating system kernel according to the configuration file. In Linux systems, GRUB is usually used as the boot loader.
3. Kernel initialization: Once the kernel is loaded successfully, the operating system kernel begins to initialize system resources, load drivers and other operations.
4. Start the system process: Then the kernel will start the init process, and then start other processes in the system to complete the system startup.

Sample Code

The following is a simple sample code that demonstrates how to use the GRUB boot loader to load a Linux operating system in an MBR:

; MBR代码示例
bits 16               ; 使用16位模式
org 0x7C00            ; MBR加载地址

start:
    jmp main          ; 跳转到主程序入口

times 510-($-$$) db 0 ; 填充剩余空间为0，使总长度为512字节
dw 0xAA55             ; MBR有效标识

main:
    ; 在这里编写引导加载器代码，加载操作系统内核

Conclusion

This article briefly introduces the functions and principles of Linux MBR, and provides a simple MBR code example. By in-depth study of the role and loading process of MBR, readers can better understand the process of Linux system booting. In practical applications, understanding the working principle of MBR is of great significance for system maintenance and troubleshooting. I hope this article can help readers better master the key knowledge of Linux system booting.

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