I'm on Ubuntu 18.04 bionic with a xfce desktop.
Today I needed a terminal and had to learn that I'm not able any more to open ANY terminal emulator. The terminal windows just close as they appear. I'm not able to see any error message. I tested xterm, qTerminal and the gnome terminal, but they all behave the same.
I also switched to the virtual terminal. There I was able to enter login information, but as I confirm an error message flashes and I'm back on the login screen.
All other software seems to work without any problems. Even CLI software like htop and shell scripts with shell output!
What did cause this problem? Yesterday I installed qgis with ubuntugis according to this instructions. Did I break something? I'm absolutely lost!
I took my camera and recorded the flashing error in the virtual terminal. Unfortunately there is no error, but just the normal login message: cf. https://linuxconfig.org/how-to-change-welcome-message-motd-on-ubuntu-18-04-server