Repair grub2 EFI and BIOS mode

To repair a broken grub boot from a linux live CD/DVD/USB. For the grub2 EFI boot from uEFI mode and BIOS for BIOS mode.

Then install boot-repair tool from PPA

#Add PPA

sudo add-apt-repository ppa:yannubuntu/boot-repair

#Update apt

sudo apt-get update

#Install boot-repair

sudo apt-get install -y boot-repair

#Run boot-repair as sudo

sudo boot-repair

The use the automatic repair (recommended) mode if you are a beginner.