Ubuntu – Motherboard replaced – How to recover GRUB

grub2mbrunetbootin

I had a dual boot setup on my Dell laptop with Ubuntu 16.04 and Windows 10. The tech replaced the motherboard and now I'm not able to boot. I am trying to restore GRUB – I installed a version of Ubuntu 16.04 on an USB stick, following the instructions on this site. Then I tried to boot from USB, but received this message:

Missing operating system
Selected boot device failed.

Can somebody tell me how to proceed?

Best Answer

Part 1 - Creating the installation media

3rd party installation media creation tools like Unetbootin are not creating the USB installation media properly in many cases. A tool to create a correctly working installation media is GNOME Disks, it's available in the repositories of nearly every Linux distribution.

Open Disks - select Restore Disk Image from the menu on the top right.
Choose the ISO file and the USB drive to write it to, then start restoring.

In case you have no access to a Linux operating system and have to do it from within Windows, you can create the installation media with the diskpart tool from a running Windows system.

Open Command prompt as administrator and execute :

diskpart
list disk  
select disk *  
clean  
create partition primary  
active  
format fs=fat32 quick  
assign letter=**  
exit

Note : * = number of USB drive | ** = select a free drive letter
Now mount the ISO file and copy the content to the USB disk.

Part 2 - Reinstalling the GRUB boot loader

Boot from the Ubuntu installation media - select the option Try Ubuntu without installing.
Once you are on the Live desktop ... open a terminal and execute the following commands.

Important information concerning the USB boot options :

Choose the USB entry with UEFI in front, in case the systems are installed in EFI mode and
the USB entry without UEFI in front, in case the systems are installed in legacy BIOS mode.

In case your computer has UEFI BIOS execute these commands :

sudo mount /dev/sdXXX /mnt
sudo mount /dev/sdXX /mnt/boot/efi
for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
sudo chroot /mnt
grub-install /dev/sdX
update-grub  
exit

Note : sdX = disk | sdXX = EFI partition | sdXXX = system partition

In case your computer has legacy BIOS execute these commands :

sudo mount /dev/sdXX /mnt  
sudo grub-install --boot-directory=/mnt/boot /dev/sdX  
for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done  
sudo chroot /mnt  
update-grub
exit

Note : sdX = disk | sdXX = system partition

You can identify disk and partition numbers by using GParted (included in the installation media).

Additional information : Do not forget to disable hibernation and Fast startup in Windows !
Then shutdown the PC completely, do NOT restart - otherwise it will always start Windows.

Easiest way is with Grub

It is cumbersome controlling grub from Windows. A third party application to access Ubuntu from Windows and some hacking is required. However from the top part of this post: How to change the order on my dual booting distros, you can setup grub to automatically reboot to the last menu option. So when you initially boot with windows, and it wakes up at 2 am to run updates, grub will reload Windows so it can gracefully finish updates.

When you manually reboot and pick Ubuntu from grub all your next reboots automatically load Ubuntu. This feature works equally well if you have bugs in the current kernel and want grub to automatically reboot into an older kernel version you selected.

How to get Grub to repeat last boot selection

This is fairly straight forward. Using sudo powers edit /etc/default/grub and change the following:

#GRUB_DEFAULT=0 # Rather than option #1, we'll always default to last boot choice.
GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true

The first line you will be commenting out and right below that insert the next two lines.

Save the file and type in the terminal:

sudo update-grub

Ubuntu command line to reboot into Windows

Currently you use something like this:

sudo grub-reboot x # Where x is Windows zero-based grub menu number
sudo reboot now

From this modified Stack Exchange answer you can use the grub default to reboot into Windows. Copy this code into your ~/.bashrc file:

function reboot-to-windows {
    WINDOWS_TITLE=`grep -i "^menuentry 'Windows" /boot/grub/grub.cfg|head -n 1|cut -d"'" -f2`
    sudo grub-set-default "$WINDOWS_TITLE"
    sudo reboot
}

Save the ~/.bashrc file with new reboot-to-windows function.
Close your current terminal session.
Open a new terminal session for changed ~/.bashrc to be loaded.
You could type : ~/.bashrc to reload it into the existing terminal session but some people recommend against do this.

To reboot into Windows from the command line use:

reboot-to-windows

If Windows automatically restarts when you aren't looking, Windows is rebooted. This allows Windows automatic updates to be processed normally over multiple-reboot cycles Windows sometimes uses.

Best Answer

Part 1 - Creating the installation media

Part 2 - Reinstalling the GRUB boot loader

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