Ubuntu – Ubuntu 18.04 screen goes black after connecting external monitors


I've had a setup that's been working for several months. My laptop has been connected to a Dell dock that's been connected to two Dell monitors. The laptop has been running Ubuntu 18.04 with the lid closed.

As of some hours ago, when I connect the dock, first all three screens appear to work, but after a few seconds all of the three screens turn black. After that, the computer keeps running but the screens stay black. Even if I disconnect the dock the laptop screen will stay black, and I have to restart it by pressing its physical button.

I haven't done anything sophisticated recently AFAIK, the only thing I can think of is that I deleted some .gz files in the var/logs folder (`sudo rm *.gz), but that should be safe.

  1. How can this be fixed?
  2. Is there any way to regain control of the computer after disconnecting the dock without restarting it?

I can connect one of the monitors directly to the laptop via HDMI and that works, but I don't have ports enough to connect both of the monitors in that way.

Best Answer

Problem and solution confirmed on a Lenovo T460s, running Ubuntu 18.04 from an LUKS encrypted volume with a dock/external monitor setup. After updating to kernel 4.15.0-44, I was able to have a visible login screen only when disconnected from the dock/external monitor. When connected to the dock using kernel -44, everything went black after applying the encryption key. Upgrading to kernel 4.15.0-45 solved the problem. Now the login screen displays also when the computer is docked with an external monitor. Thanks, sg2!

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