# This method requires you to boot into your Linux install first.

# On BIOS systems (sdX is the device where grub is installed)
grub-mkconfig -o /boot/grub/grub.cfg
grub-install --target=i386-pc /dev/sdX

# On EFI/UEFI systems (the bootloader id can but adjusted to suit your distro)
grub-mkconfig -o /boot/grub/grub.cfg
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=EndeavourOS-grub

# This method requires you to boot from a Linux live USB.
# (sdXY is your boot partition)

fdisk -l
sudo mount /mnt /dev/sdXY
mount -t proc none /mnt/proc
mount -o bind /dev /mnt/dev
mount -t sysfs sys /mnt/sys
sudo chroot /mnt /bin/bash
update-grub
/usr/sbin/grub-install --recheck --no-floppy /dev/sda
sync & reboot