Ubuntu and many other Linux distributions use the GRUB2 boot loader. If GRUB2 breaks—for example, if you install Windows after installing Ubuntu, or overwrite your MBR—you won’t be able to boot into Ubuntu.
You can easily restore GRUB2 from a Ubuntu live CD or USB drive. This process is different from restoring the legacy GRUB boot loader on older Linux distributions.
This process should work on all versions of Ubuntu. It’s been tested on Ubuntu 16.04 and Ubuntu 14.04.
The Graphical Method: Boot Repair
Boot Repair is a graphical tool that can repair GRUB2 with a single click. This is the ideal solution to boot problems for most users.
If you have the media you installed Ubuntu from, insert it into your computer, restart, and boot from the removable drive. If you don’t, download a Ubuntu live CD and burn it to a disc or create a bootable USB flash drive.
When Ubuntu boots, click “Try Ubuntu” to get a usable desktop environment.
Ensure you have an Internet connection before continuing. You may need to choose a Wi-Fi network and enter its passphrase.
Open a Terminal window from the Dash and run the following commands to install and launch Boot Repair:
sudo apt-add-repository ppa:yannubuntu/boot-repair sudo apt-get update sudo apt-get install -y boot-repair boot-repair
The Boot Repair window will automatically scan your system after you run the
boot-repair command. After it scans your system, click the “Recommended repair” button to repair GRUB2 with a single click.
You can choose to use the advanced options here, but Ubuntu’s wiki recommends you not use the advanced options unless you know what you’re doing. The recommended repair option can fix most…