Cannot login after partitioning

Question

I‘m on a dualboot Windows 10 / Ubuntu 19.10. I tried to assign more storage to my ubuntu partition: I shrank the windows partition in GParted. Then I did a reboot. After that I tried to login to Ubuntu. After a short black screen I always return to the login screen. Hence I cannot login to ubuntu. What is the problem? How can I log back in without reinstalling ubuntu?

More details (listing everything I did before and since the problem occurred):

• I downloaded lutris (without any error).
• I shrank the windows partition (Please ignore my more than naive approach to partitioning; still a noob).
• Reboot —> Login didn‘t work —> windows login worked —> reboot —> ubuntu login still didn‘t work.
• System details: Lenovo Yoga 260, Dualboot Windows10/Ubuntu19.10, lightdm.

What I‘ve tried:

• Checked permissions for Xauthority which were fine.
• Switched login manager to see whether the problem is due to lightdm (see Ubuntu login-loop).
• Logged into console (Ctrl + Alt + F3) and then started desktop with „sudo startx“ which started a session as root but didn‘t give me access to my home folder.

Answer 1

I was able to solve the problem. Here's the procedure I followed:

1. I created a bootable live usb and started an install session.
2. When the installer asked about the installation type I clicked "Something else" which brought me to the partitioning screen.
3. I then created a 300MB EFI Primary Partition.
4. After that I aborted the installation process and rebooted. --> Problem solved.

I then solved my the first problem (assigning more storage to ubuntu) by following this tutorial.