Installing Ubuntu 18.04 Bionic Beaver on Lenovo G50-45

My Lenovo G50-45 has Windows 10 and Ubuntu 16.04, Debian 9 and two more partitions to install whatever Linux I feel like.

I downloaded Ubuntu 18.04 Desktop ISO on 27 April 2018 and tried to install on spare partition. It failed to install Grub with error message 'grub-efi-amd64-signed' package failed to install target/ and also wiped menu entries of Ubuntu 16.04 and Debian making my system unbootable.

I had to boot again on Ubuntu 18.04 Live USB, install and run Boot Repair to get the menu entries back.

Today I installed Ubuntu 18.04 once again with following command:

sudo ubiquity -b

which installed without Grub.

After login in Ubuntu 16.04 I updated grub and got the entries of Ubuntu 18.04 and could boot Ubuntu 18.04.

But for anybody trying to install Ubuntu 18.04 without any other Linux present should use following procedure on AMD machines:
 

1) Boot Ubuntu Live DVD/USB in testing mode and open terminal
2) Run installation process without installing bootloader by:
sudo ubiquity -b
3) Press "Continue testing" after installation is over.
4) Mount newly installed file system into /mnt:
sudo mount /dev/sda2 /mnt
sudo mkdir /mnt/boot/efi
sudo mount /dev/sda1 /mnt/boot/efi
for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done
(where sda2 is the root partition and sda1 is the efi partition)
5) Load efivars by:
sudo modprobe efivars
6) Reinstall grub-install for a 64bit version
sudo apt-get install --reinstall grub-efi-amd64
sudo grub-install --no-nvram --root-directory=/mnt
7) Change root to /mnt and update grub
sudo chroot /mnt
sudo update-grub
8) Move and rename the installed bootloader
cd /boot/efi/EFI
sudo cp -R ubuntu/* BOOT/
cd BOOT
sudo cp grubx64.efi bootx64.efi
9) Reboot the system.