Can linux be mbr booted?

Linux can be booted by mbr. In a Linux system, when the system is started from the local hard disk, system control is first transferred to the partition containing the operating system boot file according to the setting of the MBR (Master Boot Record) in the first sector of the hard disk; or directly based on The boot information in the MBR record calls the boot menu (such as GRUB).

Linux operating system boot process

##Power on self-test

When the server is turned on, it will perform a power-on self-check to detect whether hardware devices such as CPU, memory, graphics card, keyboard, etc. are faulty. If there are no faults, it will hand over system control according to the preset boot sequence. Under normal circumstances, this is the machine hard drive.

Summary: Detect the first device that can boot the system, such as a hard disk or optical drive

MBR boot

When booting from the local hard disk system, first transfer system control to the partition containing the operating system boot file based on the settings of the MBR (Master Boot Record) in the first sector of the hard disk; or directly call the boot menu (such as GRUB) based on the boot information in the MBR record ).

MBR size is 512 bytes, which stores pre-boot information, partition table and other information.

Summary: Run the startup GRUB boot program placed in the MBR sector

GRUB menu

For the Linux operating system, GRUB (unified Boot loader) is the most widely used multi-system boot program. After the system control is transferred to GRUB, the boot menu will be displayed for the user to choose, and the Linux kernel file will be loaded according to the selected option (or the default value), and then the system control will be transferred to the kernel.

CentOS 7 uses the GRUB2 boot bootloader.

GRUB is the first 446 bytes of the MBR program.

Summary: The GRUB boot program obtains the settings and path locations of the kernel and image file system by reading the GRUB configuration file /boot/grub2/grub.cfg

Loading the Linux kernel

The Linux kernel is a pre-compiled special binary file, which is between various hardware resources and system programs and is responsible for resource allocation and scheduling. After the kernel takes over system control, it will fully control the running process of the entire Linux operating system.

In CentOS 7 system, the default kernel file is located at "/boot/vmlinuz-3.10.0-514.el7.x86_64".

Summary: Load the kernel and image file system into memory

init process initialization

After the kernel is loaded, the first program to run It is "/sbin/init" (the running program is called a process). The init process is responsible for completing the initialization of the entire system and finally waiting for the user to log in.

Summary: Load the hardware driver, and the kernel loads the init process into the memory to run

Extended knowledge: MBR sector failure analysis

Cause of failure

Damage caused by viruses, Trojans, etc.

Incorrect partition operation, disk read and write misoperation

Fault phenomenon

Cannot find the boot program, startup is interrupted

Unable to load the operating system, black screen after booting

Solution ideas

Backup files should be prepared in advance

Boot into rescue mode with the installation CD
Restore from the backup file
Simulate MBR sector failure and repair
The MBR is located in the first physical sector of the first hard disk (/dev/sda). 512 bytes in total

Steps

1. Create a disk partition

2. Format, and Mount

3. Back up the MBR sector data to the /dev/sdb1 disk. At this time, the MBR sector in the sda ​​disk has been backed up to the mbr.bak file of sdb1. middle.

4. Simulate the destruction of the MBR sector of sda and overwrite the first 512 bytes of sda with null characters.

5. Restart init6

##Establish the mount point/backupdir, mount sdb1 for use, copy the backed-up mbr.bak file back to sda, and finally enter exit to exit. After exiting, the system will automatically restart!

Extract from backupdir and overwrite it

exit exit repair successfully

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