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5.3. Reinstalling GRUB

This section describes the process for reinstalling the GRUB bootloader and recreating the configuration. Unlike legacy GRUB, which required users to manually create entries, GRUB2 will scan the system for bootable systems and automatically create the menu configuration. There are a number of reasons to reinstall GRUB:
The boot menu does not include an available operating systems.
The bootloader has been overwritten during installation of Windows or another operating system.
You have chosen not to use anaconda to install grub.

5.3.1. Refreshing GRUB configuration

To recreate the GRUB configuration from a booted system, use the grub2-mkconfig utility. The program will scan your system and create menu entries for what it finds. You should also use grub2-mkconfig after customizing menu entries, a process described in Section 5.4, “Configuring the GRUB Bootloader”
Refresh GRUB configuration on a BIOS system:
          # grub2-mkconfig -o /boot/grub2/grub.cfg
Refresh GRUB configuration on UEFI systems:
          #grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg