Grub doesn't show both Ubuntu installations
I the os-prober utility wasn't executable. I had to run this:
sudo chmod +x /etc/init.d/30_os-prober
and then
sudo update-grub2
I the os-prober utility wasn't executable. I had to run this:
sudo chmod +x /etc/init.d/30_os-prober
and then
sudo update-grub2