It may sound strange but in all the years I’ve been using Ubuntu only one or two distro upgrades worked without problems. All the other attempts resulted in long lists of errors during the installation of the new packages. And the last upgrade from 17.10 to 18.04 ended in a black screen with a nice blinking cursor and nothing else.
After a reboot Ubuntu was bootable but halfway starting the services it stopped and left me with another blinking cursor. Because Ubuntu was bootable i decided to boot into recovery mode and to drop into the root shell prompt. To start Ubuntu into safe mode (Recovery Mode) hold down the left Shift key as the computer starts to boot. If holding the Shift key doesn’t display the menu press the Esc key repeatedly to display the GRUB 2 menu. From there you can choose the recovery option.
I entered the following command: sudo apt upgrade and the upgrade process continued where it stopped. After installing the new packages the process freezed so i rebooted my pc and repeated the same steps. When the upgrade was finished i rebooted my pc and logged into the recovery mode again to repair all the broken packages. When the all the broken packages were repaired i rebooted my pc and Ubuntu 17.10 was upgraded to 18.04.
This may seem a lot of work and a lot of waiting to you and it is. But.. there’s an easier way! You can simply (re)install Ubuntu 18.04 from a dvd or a flash drive, this will work faster to fix an failed upgrade. But it’s also less fun 😉