Problem with dual display on Linux


I’m new to PsychToolBox and I’m trying to make dual display possible on my laptop that runs on Linux, for example, experiment presentation on one monitor and Matlab codes showing on the other monitor. The PTB version I have is 3.0.18, and my operating system is Ubuntu 20.04.

I followed the instructions in this post and ran “PsychLinuxConfiguration” as root. The output showed that my system does not have the /etc/X11/xorg.conf.d/ folder. I allowed it to create this folder. Afterwards, I ran the “XOrgConfCreator” and the “XOrgConfSelector” commands to create a configuration file and copy it to the /etc/X11/xorg.conf.d/ folder. However, after I had done all these, I could no longer login Ubuntu. Moreover, Ubuntu couldn’t restart normally unless I deleted the /etc/X11/xorg.conf.d/ folder.

Is this a bug between PTB and the current Ubuntu version? Is there a way to make dual display possible on Ubuntu 20.04? Otherwise, what is an Ubuntu version on which “XOrgConfSelector” works (I don’t mind switch to an older version of Ubuntu)?

Thanks in advance for your help!


Ubuntu 20.04-LTS + PTB 3.0.18 is the most well tested and well supported configuration of all possible PTB + operating system combos at this point, and what you did should work just fine.

If you downloaded Psychtoolbox from us, PsychLinuxConfiguration would have run automatically, only when installing via sudo apt ... do you need to run it manually, but this doesn’t matter here.

Deleting the file inside /etc/X11/xorg.conf.d/ will be enough on login failure, no need to delete the folder, which is needed.

So something went wrong when creating the xorg.conf file by XOrgConfCreator, i guess. Maybe due to some exotic or unsupported graphics hardware setup. NVidia and especially involving the NVidia proprietary driver is a potential troublemaker and strongly discouraged.

What’s your laptop model, graphics card, etc.? Is this a strongly discouraged NVidia Optimus laptop or using NVidia’s proprietary driver - which is also strongly discouraged? What’s the output of ~/.local/share/xorg/Xorg.0.log after a failed login?

Note: If this takes me more than 5 minutes more time to resolve, because it is something not super-trivial, you will have to buy priority support, or i won’t help you further: help PsychPaidSupportAndServices.


Thank you so much for getting back to me! My laptop model is DELL Precision M3800. It has two graphics cards, Intel HD Graphics 4600 (driver=i915) and NVidia Quadro K1100M (driver=NVidia v390.144). So I guess my laptop is both NVidia Optimus and using NVidia’s proprietary driver, both of which are strongly discouraged?

I suppose I can try following the instructions in the sychtoolbox/PsychHardware/LinuxDrivers/NVidiaOptimus/ folder (my X.Org version: 1.20.11) and see if that would make everything work? Do you have any other suggestions? Thank you!

Those Optimus hacks don’t work with Ubuntu 20.04LTS or X-Server 1.20 anymore. As the K1100M is an old Kepler family gpu, which still was supported ok by nouveau, i’d switch back to the purely open-source nouveau driver for NVidia. XOrgConfCreator should work then again. Intel will do display and rendering, and the end of “help HybridGraphics” will explain you how to optionally use the NVidia for render-offload which may or may not give a bit of a speed boost, ie. section " Tell Matlab or Octave to use the dGPU for rendering with Psychtoolbox". At least this way you also get proper timing and timestamping.