What is the role of linux MBR

In Linux, the role of MBR is to store the startup boot program. The functions of the startup boot program are: 1. Load the kernel of the operating system; 2. Have a menu that allows the user to choose which system to boot; 3. Call other startup boot programs, which is the key to multi-system startup. .

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

What is Linux MBR? What is the use?

MBR is the abbreviation of English Master Boot Record, and the Chinese meaning is master boot record. The first sector of track 0 of the hard disk is called MBR. Its size is 512 bytes, and this area can be divided into 3 parts.

• The first part is the pre-boot area (pre-boot area), occupying 446 bytes;

• The second part is the Partition table area ( Partition table), accounting for 64 bytes. This area is equivalent to a small program. Its function is to determine which partition is marked as the active partition, then read the boot area of ​​that partition and run the code in that area;

• The third part is the sector end mark, occupying 2 bytes.

The most important function in MBR is to store the boot boot program.

The role of the startup boot program

The function of BIOS is to self-test and then read the startup boot program from the MBR. Then, the most important function of the bootloader is to load the kernel of the operating system. Of course, the bootloader for each operating system is different.

The file format of each operating system is different, so the startup boot program of each operating system is also different. Different operating systems can only load their own kernels using their own bootloaders. If I only have one operating system installed on my server, the boot loader for that operating system will be installed in the MBR. When the BIOS calls the MBR, it reads the startup boot program and the kernel can be loaded.

But sometimes, there are multiple operating systems installed in my server, but there is only one MBR. So which operating system boot program is installed in the MBR?

Obviously, one MBR is not enough. Each hard disk can only have one MBR and cannot be changed, so it is impossible to increase the number of MBRs. The system can only divide one sector in each file system (which can be regarded as a partition), which is called the Boot Sector. The boot loader can also be installed in the boot sector of each partition, that is, the boot loader can be installed in the MBR and in the boot sector of each individual partition. In this way, multiple operating systems can be installed on the same server (each operating system must be installed in a different partition), and each operating system can be booted.

There is another problem. The BIOS can only find the boot boot program in the MBR, but not the boot boot program in the boot sector of the partition. So, to complete multi-system boot, our method is to increase the function of the boot boot program so that the boot boot program (GRUB) installed in the MBR can call other boot boot programs in the boot sector of the partition.

Therefore, the startup bootloader has the following functions:

• Load the kernel of the operating system. This is the most important function of the bootloader.

• Have a menu that allows users to choose which system to start. If you have installed dual Windows systems on a server, you should have seen a similar selection menu, but this selection menu is provided by the Windows startup boot program, not GRUB.

• You can call other startup boot programs, which is the key to multi-system startup. However, it should be noted that the Windows startup boot program cannot call the Linux startup boot program, so we generally recommend installing Windows first and then Linux. This is to install the Linux startup boot program into the MBR and overwrite the Windows startup boot program. .

Of course, this installation sequence is not absolute. Even if Windows is installed in the end, we can also manually install GRUB to ensure that the Linux startup boot program is still installed in the MBR. .

The picture below shows us the function of starting the boot program.

The role of bootloader

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