Linux MBR: an important part of the system startup process

When we start the computer, the startup process of the operating system is actually a complex and sophisticated process. Among them, MBR (Master Boot Record) is an important part of the system startup process. In the Linux system, MBR plays a linking role. It is responsible for booting and loading the operating system and passing control to the kernel. This article will delve into the role, structure and specific code examples of Linux MBR.

1. The role of MBR

MBR is located in the first sector of the hard disk (usually track 0, magnetic surface 1), with a size of 512 bytes. It contains the boot loader (Boot Loader) and hard disk partition table. When the computer starts, the BIOS (Basic Input/Output System) reads the MBR of the hard disk and hands control to the boot loader in the MBR.

In Linux systems, common boot loaders include GRUB (GRand Unified Bootloader) and LILO (LInux LOader). They load the kernel image (vmlinuz) and initialize the memory file system (initrd) from the hard disk to boot the system.

2. The structure of MBR

The structure of Linux MBR is as follows:

• Boot Code (Boot Code): occupies the first 446 of MBR Bytes, responsible for loading the operating system's boot loader.
• Partition Table (Partition Table): Occupies the next 64 bytes of the MBR and records the hard disk partition information. Each partition table entry is 16 bytes.
• MBR Signature (MBR Signature): Occupies the last two bytes of the MBR and is used to identify whether the sector is a valid MBR.

3. Specific code example

The following is a simple example code to show how to write a custom boot loader to the MBR of the hard disk. Please note that this requires root access and caution to prevent data loss.

# 下载一个示例的引导加载程序
wget http://example.com/bootloader.bin

# 将引导加载程序写入硬盘的MBR
sudo dd if=bootloader.bin of=/dev/sda bs=446 count=1

In the above example, we write a boot loader named bootloader.bin to the hard disk through the dd command sda in the MBR. This bootloader can be customized and used to load a Linux system.

4. Summary

Linux MBR is a crucial part of the system startup process. It is responsible for booting and loading the operating system and passing control to the kernel. Understanding the structure and function of MBR can help us gain a deeper understanding of the system startup process. Through specific code examples, we can operate the MBR, customize the boot loader, and expand control over system startup.

I hope this article will help everyone understand Linux MBR, and also remind everyone to be careful when operating MBR to avoid damage to system data.

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