Ok so I was installing Kubuntu for a desktop system and the bootloader kept failing to install. I went online and could not find any solution to the problem:
Code:
grub-efi-amd64-signed failed to install
So I am posting the workaround here.

The issue is the installer is not correctly retrieving the packages on the installation CD.

So first thing we're going to do is mount the new system.
Code:
 sudo su
Code:
 mount /dev/sda2 /mnt
Code:
 mount -o proc proc /mnt/proc
Code:
 mount -o sysfs sys /mnt/sys
Code:
 mount -t bind dev /mnt/dev
If you're on an EFI system don't forget to
Code:
 mount /dev/sda1 /mnt/boot/efi
Then we need the WIFI to keep working so do this
Code:
 cp /etc/resolv.conf /mnt/etc/resolv.conf
Now chroot into the new system.
Code:
 chroot /mnt
And edit the sources.list so it can retrieve the GRUB packages online instead of fetching them locally from the disk.
Code:
 nano /etc/apt/sources.list
Now we need to fetch GRUB
Code:
 apt-get update
Code:
 apt-get install grub-efi-amd64-signed
And install it
Code:
 grub-install /dev/sda
Finally update it
Code:
 update-grub
Sorted. Hopefully didn't miss a step

This tutorial also shows you how to reinstall or update grub on any ubuntu as the general principles are the same .

I've also just realized Kubuntu now has its own dedicated forum. It's been a while!