GRUB is a multi-system boot management tool that is used to load and select the operating system kernel at boot time. It works in three stages: Stage 1 loads the boot sector code, Stage 2 loads the complete program and configuration files, and finally loads the kernel into memory and hands over control. Common features include support for multi-system selection, multiple file systems, command line boot, and configuration customization. Frequently asked questions such as missing boot menu or GRUB command line appearing after deleting Linux, which can be resolved by fixing boot or modifying the configuration. Daily maintenance is recommended to run update-grub or grub-mkconfig after update and reserve the /boot partition for improved stability.

GRUB, the full name is Grand Unified Bootloader , to put it bluntly, it is one of the first programs to run when your computer is booted. Its main task is to load and pass control to the operating system kernel before the operating system starts. You can understand it as "the guide of the operating system".

Why do you need GRUB?

Modern computers often have more than one system, for example, you may have both Windows and Linux installed. At this time, a "selector" is needed to tell you which systems can be started and load the corresponding operating system into memory after selection.

GRUB is an implementation of this "selector", and it is particularly suitable for use in multi-system environments, especially Linux users, which will almost always be exposed to.

Common features include:

• List available operating systems for you to choose from
• Supports multiple file systems (such as ext4, Btrfs)
• Provides a command line interface for manual boot
• Support custom startup items through configuration files

How does GRUB work?

GRUB is divided into several stages of work, simply put:

1. Stage 1 (Phase 1) : The BIOS or UEFI hand over control to the boot sector (MBR or EFI partition) of the hard disk, and the code here will load the next stage.
2. Stage 2 (Stage 2) : This part is the truly complete GRUB program. It will read the configuration file (usually /boot/grub/grub.cfg ), display the menu, and then load the corresponding kernel and initramfs according to your choice.
3. Start the operating system : Once a system is selected, GRUB will load the kernel into memory and hand over the control, and the operating system will start taking over.

Although this process may seem complicated, most of the time users will not notice it. It will only jump out for you to see when the system is updated, installed, or dual-system conflicts.

FAQs and usage tips

If you only use one system on a daily basis, you may rarely encounter GRUB problems. But in the following situations, you may deal with it:

• After installing Linux, you cannot see the boot menu → Usually GRUB is not installed correctly or is overwritten
• GRUB command line still appears after Linux is deleted → Windows boot needs to be repaired or bootstrap reinstalled
• If you want to adjust the default startup item or timeout time → You can modify GRUB_DEFAULT and GRUB_TIMEOUT in the /etc/default/grub file

Some simple maintenance suggestions:

• After updating the system, remember to run update-grub (Debian/Ubuntu) or grub-mkconfig (Arch/Fedora)
• If you encounter a black screen or command line interface, don't panic. Try entering normal to enter to see if the menu can be restored.
• Multi-system users recommend a separate partition mount /boot to help avoid GRUB corruption.

Let's summarize

GRUB is a tool that helps you start the system, especially suitable for multi-system environments. The technical details behind it are quite deep, but it is not difficult to master on daily use. As long as you don't frequently mess with the system partition, it can usually stay in the background to work quietly.

Basically that's it.

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