How to fix the inability to log in to local users with the correct passwords?

Question

ubuntu

Did sudo apt-get update && sudo apt-get upgrade && sudo apt-get dist-upgrade
Installed Gambas3.
Installed version 5.0.10 on top of VirtualBox 5.0.8 with sudo dpkg -i virtualbox_5_0_10.deb packagename
Immediately after that installed version 5.0.12 on top of 5.0.10 with sudo dpkg -i virtualbox_5_0_12.deb packagename
Restarted and couldn't login to any user.
I could not enter recovery mode either (neither by an empty password, nor by the correct password of the first installed user, nor by Ctrl-D).
I understand that I am my own enemy.
But what can I fix to make it work?
Of course, I can easily reinstall the OS and all the software, since there are three partitions: swap, system and user.
But I want to figure out what's what.
How to fix the inability to log in to local users with the correct passwords?

Answer 1

Boot into a Live USB, chroot into the installed system, and change the password for the correct user again. Installing the apps mentioned shouldn't change the password, maybe just the keyboard layout is wrong?