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Sometimes, in case of troubleshooting, you may have to install a new GRUB bootloader.

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So normally GRUB2 is installed automatically, and you don't have to worry about it. The

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only thing you would do is to use GRUB2 mkconfig to write new settings to the GRUB bootloader

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configuration files. To write a GRUB2 bootloader to a completely new device, you can use the

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GRUB2 install command. And installing or reinstalling GRUB2 can be useful for troubleshooting. On

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BIOS systems, use GRUB2-install-dev-sda, and that will be enough to reinstall GRUB2. Obviously,

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you do need to verify your storage device. It should be your primary disk, and on many

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systems that should be dev-nvme-0-n1 instead of sda. If you are on UEFI, it's a little

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bit more complex, because in UEFI, there is also the cryptographic keys that are required

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for working with Secure Boot. And they need to be reinstalled as well if you are going

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to reinstall GRUB. To do so, you would use the command GRUB2-reinstall-grub2efishim,

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where the shim file contains the cryptographic keys that allow for working with Secure Boot.

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And if you have done all that, while you reinstalled GRUB, and on a system that had

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become unbootable, it should be bootable again.