Ubuntu – screen shuts down when connecting to dock

Your dock is probably not supported in linux unless its a true thunderbolt dock or has its own driver.

Please update your question with the full lspci output.

Thunderbolt 2 is the same physical connector as mini displayport , on a true thunderbolt dock the displayport is just another socket for the display card. I use an OWC thunderbolt dock this way , its almost invisible to the computer as its basically pci-e hotlpug.

If your dock is made by dell it almost certainly uses a displaylink chipset it will need a driver for it to work properly, you can get one here. It will be laggy and slow , these are barely usable in linux. http://www.displaylink.com/downloads/ubuntu

Unless you need the dock for the other ports i would just plug the monitor directly in to the thunderbolt socket, you might need an adapter.

Andrew. I experienced something similar to what you're getting. I have 18.04 with Linux 4.15.0-29-generic. This started to happen to me after I did install Nvidia Proprietary Drivers. If you updated from 16.04 where you were using proprietary drivers it can be the problem.

I would suggest to remove all the "Nvidia" drivers.

sudo apt-get --purge remove nvidia*

And maybe reconfigure X server.

sudo service gdm3 stop
sudo dpkg-reconfigure xserver-xorg

Helped me. Had it working with Nouveau.