Shulou(Shulou.com)06/03 Report--

The boot process of the system

1. energized

2. Bios initialization

memory, hard drive not plugged in properly

3. disk boot

The data inside the hard disk is stored in the form of partitions, and the magnetic head on the hard disk scans the data on the hard disk.

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track: The track of a magnetic head revolution that determines which ring the data is in

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Sectors: Determine which section of data

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System-guided processes:

#When installing dual systems, when starting windows, the magnetic head needs to jump to the c disk data position to read the data inside before starting the system.

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After the system is shut down, the power is off, the magnetic head will return to the position when the power is off, the hard disk will turn up, the disk will not jump to the c disk position, or in the default position (track 0), how to make the magnetic head jump to the c disk, read the data?

#When installing the system, load the magnetic head on the first part of the hard disk to read what data to read next, which position program to write data on sector 1 of track 0: mbr (tell the magnetic head to read c disk information after reading)

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Role of MBR:

The head reads the mbr boot record, automatically jumps to the boot partition, reads the data inside,(reads the next file) mbr Location: Track 0, sector 1, 446 bytes

Record the location of the boot partition

mbr If damaged, repair required: system cannot boot from hard disk, so use CD to enter system rescue mode

#Execute the repair command, as shown in the following note

You can't clear all the data in the device. The 64 bytes behind the 446 bytes are the partition table. After the partition table is damaged, you need to know how many blocks the device starts and ends. You need to backup the partition table. bs=446 count=1 backup

Enterprise 8 failed to reboot from hard drive, data needs to be repaired, enter rescue mode

Enter Repair from CD

** Explanation: Rescue mode will be in the mode as shown in the figure, will find the installed linux in the system, and mount it to the/mnt/sysimage directory, the data is in the CD,(the system in the disk is mounted to the CD rescue environment/mnt/sysimage, you can make operations in it to rescue, repair data) Press 1,

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Continue as shown below

Get the real system environment: chroot /mnt/sysimage/ df mount normally (convert to disk mount mode)

grub2-install /dev/nvme0n1 Write mbr again on the device. The writing tool is called

（grub2-install）

exit to leave

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Close Enterprise 8 Adjust boot from hard drive

Enterprise 8 boot successfully from hard drive

The system cannot be restarted, it has been stuck in the hard disk startup phase: 1. Hard disk damage 2.mbr There is a problem

Try to solve (debug): mbr problem

4.grub2 file boot: automatically load the kernel and initialize the image in the system according to the records in the file

eg: in rhel7

The/boot/grub2/grub.cfg file records a series of files read by the system during boot

Experiment 4 is performed according to 3, and the experimental steps are roughly as shown in the above figure.

1. Simulation question: rm -fr/boot/grub2/grub.cfg

2. Repair, as shown in the above note

Manual boot in Enterprise 8

5. kernel loading

Enterprise 7 connects Enterprise 8

Simulate the problem, restart the system, Enterprise 8 cannot restart, save as shown in the notes above, refer to 3 for specific operations

Note: Enterprise 7 does not require a step

6. System initialization mirror

7. System startup level

8. Super User Password Forgot

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