Bootloader Grub for computers with Windows 8.x or 10 (EFI and UEFI): how to re-install it


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Note: this how-to isn't meant for installing Linux Mint or Ubuntu on a computer with UEFI in full UEFI mode, but only for repairing bootloader Grub of an existing installation on such a computer. For installing Ubuntu or Linux Mint on such a computer you can use this other how-to *click*.

A modern computer with Windows 8.x or 10 has EFI or UEFI, that's running in full UEFI mode. On such a computer you might, after a successful installation of Ubuntu or Linux Mint, suddenly lose the possibility to boot Ubuntu or Linux Mint.

For example this might happen because you've reset your UEFI to its defaults, or because you've upgraded your UEFI to a later version.

Thankfully this problem is not difficult to solve. Provided that you apply the how-to below, with exact precision.

Note: this how-to is only fit for modern motherboards that run on UEFI in full UEFI mode. This is usually the case for computers that were sold with a pre-installed Windows 8.x or 10.

But this how-to is definitely unfit for older motherboards that run on an old-fashioned BIOS. This usually means a computer that was sold with Windows Vista or Windows XP pre-installed on it.

The how-to is also unfit for a modern motherboard that runs on an (U)EFI that has been configured to behave as if it were an old-fashioned BIOS. This is normally the case for a computer that was sold with a pre-installed Windows 7.

The how-to for old-fashioned BIOS can be found here.


A computer that's running in full UEFI mode, usually is a computer with a pre-installed Windows 8.x or 10 (64 bit edition). The how-to below is therefore based on a 64-bit Ubuntu, that has suddenly "disappeared" from a dual boot machine that has also Windows 8.x or 10 on it.

Note: the how-to was written for Ubuntu and not for Linux Mint. But it's fit for Linux Mint as well: the how-to is the same for both Linux editions.

This is how you do it:

1. Boot your computer from the 64-bit Ubuntu or Mint DVD (of from a Live USB with 64-bit Ubuntu or Mint on it). Select "Try Ubuntu (without installing)".

Note: only use the DVD of the Ubuntu or Mint version that you wish to repair. So for Ubuntu 16.04, use the DVD of 16.04.


2. Connect to the internet. Wireless or wired, that doesn't matter. But you need internet connection.


3. Now you need to find out which are the names of two partitions: the root partition (on which your Ubuntu has been installed) and the EFI partition (that contains the launchers of both Ubuntu and Windows).

Check this with the application Gparted Partition Editor. Gparted is present both on the Ubuntu DVD and on the Linux Mint DVD.

Tip: the root partition of your Ubuntu or Mint, will usually be formatted in EXT4. The EFI partition wil probably be formatted in FAT32, and it'll have the boot flag.

On my computer, the Ubuntu root partition is called sda5 and the EFI partition is called sda2. For the sake of clarity I'll use that situation in the rest of the how-to.


4. Now you're going to mount both partitions:

a. Launch a terminal window.
(You can launch a terminal window like this: *Click*)

b. First the root partition from Ubuntu or Linux Mint. Copy and paste the following command line into the terminal (with a right-click of your mouse you can use copy/paste):

sudo mount /dev/sda5 /mnt

Note: this command line is only valid when your Ubuntu is on sda5. Adapt it when it's different on your computer.

Press Enter.

c. Now the EFI partition. Copy and paste this command line into the terminal (with a right-click of your mouse you can use copy/paste):

sudo mount /dev/sda2 /mnt/boot/efi

Note: this command line is only valid when the EFI partition is on sda2. Adapt it when it's different on your computer.

Press Enter.

d. Then copy and paste the following command line into the terminal (this is one line):

for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done

Press Enter.


5. Now you're going to make sure that your internet connection stays alive. Copy and paste this command line into the terminal:

sudo cp /etc/resolv.conf /mnt/etc/

Press Enter.


6. Now you're going to load a certain module. Copy and paste the following command line into the terminal:

modprobe efivars

Press Enter.


7. Issue a chroot command. Copy and paste this command line into the terminal:

sudo chroot /mnt

Press Enter.


8. Re-install Grub. Copy and paste the following command line into the terminal:

apt-get install --reinstall grub-efi-amd64

Press Enter.

The execution of this command may take a while; simply wait.


9. When the previous job is done, type this command into the terminal to end chroot:

exit

Press Enter.


10. Finally the completion (unmounting), which consists out of several steps.

a. First copy and paste the following command line into the terminal (this is one line):

for i in /sys /proc /dev/pts /dev; do sudo umount /mnt$i; done

Press Enter.

b. Then unmount the EFI partition. Copy and paste this command line into the terminal:

sudo umount /mnt/boot/efi

Press Enter.

c. Now unmount the root partition from Ubuntu or Mint. Copy and paste the following command line into the terminal:

sudo umount /mnt

Press Enter.


11. Time for a reboot and a check whether all has gone well. Type in the terminal:

sudo reboot

Press Enter.


If all has indeed gone well, your Ubuntu or Linux Mint should be bootable again from the hard disk.


Want more tips?

Do you want more tips and tweaks for Ubuntu and Linux Mint? There's a lot more of them on this website!

For example:

Speed up your Ubuntu

Firefox: improve it

Chrome: tweak it

Libre Office: tune it

Solid State Drive: optimize it


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