Ubuntu Desktop 18.10 UEFI grub not booting

Question

Neither live CD nor USB image does boot in UEFI on my system. Black screen, that is all, no grub-efi does show up. So, not even coming close to the point to install or reinstall. With 18.04 UEFI ist fine and works as designed.

Answer 1

Boot from a live USB, (or the disk you used to install Ubuntu) the boot device selection in your bios may have multiple options. choose the UEFI device

Identify your boot device with sudo fdisk -l or gpartid.

chroot into your system. (/dev/sda in this example) replace sda# with your device

sudo mount /dev/sda2 /mnt #sda2 is the root partition
sudo mount /dev/sda1 /mnt/boot/efi #sda1 is the efi partition
for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done
sudo cp /etc/resolv.conf /mnt/etc/ #makes the network available after chrooting
modprobe efivars # make sure this is loaded
sudo chroot /mnt

Reinstall and update GRUB

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

or if you have a 32bit system:

apt-get install --reinstall grub-efi

then

update-grub

exit chroot with Ctrl+D

unmount everything and reboot

for i in /sys /proc /dev/pts /dev; do sudo umount /mnt$i; done
sudo umount /mnt/boot/efi #please do this. Corrupted efi partitions are not nice
sudo umount /mnt
sudo reboot

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I've referenced these answers:
https://superuser.com/a/376471/953420
https://askubuntu.com/a/681442/234305