Explore the role of Linux MBR

Linux MBR (Master Boot Record) is a special boot record stored in the first sector of the hard disk and is used to start the computer and load the operating system. Understanding the capabilities of the Linux MBR is important for a deep understanding of the computer boot process and operating system loading process. This article will introduce the functions of Linux MBR and provide specific code examples to help readers better understand.

1. Overview of Linux MBR

Linux MBR contains two parts of information: the main boot code and the partition table. The master boot code is a small program that initiates the boot process and transfers control to the operating system's boot program. The partition table records hard disk partition information, including the starting position, size and partition type of each partition.

2. Functions of Linux MBR

1. Start the computer

When the computer is turned on, the BIOS will first load the first sector on the hard disk. area (i.e. Linux MBR) and execute the boot code in it. The boot code initializes the system environment and loads the operating system's boot program.

2. Load the operating system

Linux MBR will read the partition table information, find the partition where the operating system is located based on the partition information recorded in it, and transfer control Hand it over to the boot program in that partition (such as GRUB or LILO). The boot program will continue to load the operating system's kernel and file system, and finally complete the system startup process.

3. Specific code example

The following is a simple example code that demonstrates how to read the partition table information in the Linux MBR:

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

#define SECTOR_SIZE 512
#define PARTITION_TABLE_OFFSET 446
#define PARTITION_TABLE_ENTRY_SIZE 16

int main() {
    int fd = open("/dev/sda", O_RDONLY);
    if (fd == -1) {
        perror("open");
        return 1;
    }

    unsigned char mbr[SECTOR_SIZE];
    if (read(fd, mbr, SECTOR_SIZE) != SECTOR_SIZE) {
        perror("read");
        close(fd);
        return 1;
    }

    unsigned char* partitionTable = mbr + PARTITION_TABLE_OFFSET;
    for (int i = 0; i < 4; i++) {
        printf("Partition %d:
", i+1);
        printf("Status: %02x
", partitionTable[i*PARTITION_TABLE_ENTRY_SIZE]);
        // 输出更多分区信息，如起始位置、分区类型等
    }

    close(fd);
    return 0;
}

The above code opens the hard disk device File /dev/sda, reads the first sector of the hard disk (i.e. Linux MBR), and parses the partition table information in it. Readers can extend the code according to their own needs and output more partition information.

Conclusion

By having an in-depth understanding of the functions of Linux MBR and combining it with specific code examples, readers can better understand the computer boot process and operating system loading process. I hope this article can help readers deepen their understanding of Linux MBR and gain a deeper understanding of computer systems.

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