Usually if you get the grub boot loader and it doesn't show any boot options, it's because grub was not installed correctly and/or the partition that it is supposed to be on has changed or does not exist. It can also happen if you install Linux to one drive, but the boot loader to another by accident, whether EFI or MBR/Legacy mode.
You can normally fix your booting/bootloader/MBR/EFI it by chrooting into your root partition:
#become root
sudo su
#make a directory called target where we will mount your root partition
mkdir /target
#mount /dev/sda3 to target (change to match your root partition)
#eg if your root is /dev/sda2 then change it below
mount /dev/sda3 /target
#if you are using EFI mount your EFI partition to /target/boot/efi (assume here it is /dev/sda1)
mount /dev/sda1 /target/boot/efi
#we need to mount dev proc and sys for the chroot to work like it was booted normally so we can fix it
for mount in dev proc sys; do
mount -o bind /$mount /target/$mount
done
#now chroot
chroot /target
#run grub install on the drive that you installed Linux to
grub-install /dev/sda
--bootloader-id realtechtalk.com
Then in your EFI BIOS it will show as "realtechtalk.com". You can change to what's suitable for you, otherwise it's the OS default (eg. Mint and Ubuntu will present the name Ubuntu).
For the bootloader-id to work you need to do a normal grub-install first which creates the OS defaut, at least in Ubuntu based. For Debian based you need to specify --bootloader-id debian and then do secondary grub-install with your desired bootloaderid.
Read more grub bootloader-id issues on this here on Step 5 of this convert GRUB MBR to EFI guide
If you are using EFI and you are fixing things because the wrong drive or partition received the GRUB bootloader, you'll need to update /etc/fstab to fix the mount for /boot/efi.
#fix your /boot/efi mount
blkid /dev/sda1
/dev/sda1: UUID="21F4-BED9" TYPE="vfat" PARTUUID="ffaee6e2-01"
In our example above the UUID is 21F4-BED9
Edit /etc/fstab by updating the UUID to the correct value for /boot/efi
With the update
Be sure to save the file and then type "mount -a" to make sure everything can mount OK and that there are no errors in fstab.
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