Black screen on virtual console with GeForce 9600M GT & 9400 M

Hi! Recently a friend gave me an old but lightly used MacBook Pro (15-inch, Late 2008) with two Nvidia GeForce graphics processors, a 9600M GT and a 9400 M. I wiped the disk, installed Kubuntu 18.04 and created two user accounts. Initially fast user switching was working: I was able to start a parallel session as the other user either graphically, via the Application Launcher and Switch User, or textually, via Ctrl+Alt+Fn+F2 and the command line. But soon a system notification prompted me to open the Driver Manager system settings module and change from the default option, “Using X.Org X server – Nouveau display driver from xserver-xorg-video-nouveau”, to “Using NVIDIA binary driver - version 340.106 from nvidia-340 (Recommended Driver)”. After making that change, in the launcher, clicking Switch User and then clicking Switch results in a black screen. To get back to the session already running, I enter Ctrl+Alt+Fn+F1, where I get a lock screen with most of the text missing and only a few random-seeming letters remaining. After I enter my password, all appears normal again. Changing virtual terminals using Ctrl+Alt+Fn+F2 or any other F-key besides F1 also produces a black screen. Selecting the Nouveau driver and rebooting restores the other virtual terminals and fast user switching. I reselected the Nvidia driver, restarted the X server with -logverbose 6, attempted a user/console switch and ran nvidia-bug-report.sh, so I have an nvidia-bug-report.log.gz file to share, but I can’t see any attachment controls. I understand that the 9600M GT and 9400 M are considered legacy hardware, and in the Linux world there are never any guarantees, but any advice here would be very helpful and much appreciated. Thanks!
nvidia-bug-report.log.gz (112 KB)

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More of a problem is that this is Apple HW which often has its own proprietary quirks when it comes to gpu switching. The nouveau driver contains some support for that while the proprietary driver does not.

Thanks for the help finding the attachment link. The bug report log is now attached. I’ve done some googling and tinkering before posting here, so I realize I may end up having to choose between smoother, faster graphics performance with no fast user switching nor virtual consoles (Nvidia driver) or rougher, slower graphics performance with fast user switching and virtual consoles (Nouveau driver). It’d be great if I could have it all by editing some config file, using a different driver version or some such. But in the end I will be happy just getting the best advice I can find from someone who understands how this driver stuff works. :-)

Maybe start by checking out gpu switching:
https://lwn.net/Articles/707616/
https://www.kernel.org/doc/html/latest/gpu/vga-switcheroo.html#manual-switching-and-manual-power-control

And thanks again, generix, this time for the articles. I read them multiple times and learned a lot! But those articles are concerned primarily with switching between the two graphics processors and managing the power on the discrete one. All I want to do is get the integrated GPU, which is already working fine displaying my first user session on virtual terminal 1, to be able to switch to the other virtual terminals and display them too. After more research and poking around, I combed through the script-generated bug report attached to my first post, and I found something that seems relevant comparing the Xorg.0.log and Xorg.1.log sections. When starting up display 0 on VT1 (Xorg.0.log), just after adding the DRM device for each GPU, Xorg comes to the “nvidia” OutputClass in the config file and adds /usr/lib/nvidia-340/xorg to the search path for loadable Xorg server modules. There are then many more lines indicating Xorg has found and is using the Nvidia driver. But when starting up display 1 on VT2 (Xorg.1.log), adding each DRM device results in the error, “failed to set DRM interface version 1.4: Permission denied”, and Xorg proceeds to use other drivers. This suggests to me that the Nvidia driver is working fine for me and what I actually have is a problem with Xorg configuration. So maybe I should pursue this further on Kubuntu Forums, but if anyone here has any more advice I’d certainly appreciate it.

I have the same problem, except that I am using Xubuntu 18.04 so virtual terminal numbering is different. My MacBook has GeForce 9400M only.

Did you find anything relevant on Ubuntu forums?

I have another laptop which uses the same nvidia-340 driver and which does not have this problem. It has VGA compatible controller: NVIDIA Corporation G84GLM [Quadro FX 570M] (rev a1)

Nope, JarnoIS, never did. Fast user switching and multiple virtual terminals work with the nouveau driver, so I’m using that one.