Unable to run second X server on second video card


I have a system set up with two NVidia cards:

  • a GTX 1070 - main, used when booting
  • a GTX 750 Ti card

They are both connected to the same monitor - a Dell U2515H. The 1070 is connected to the mini display port, while the 750 Ti is connected to the HDMI port.

I have tried the following:

  1. Boot using 1070
  2. Log in to Gnome
  3. Start a second Xorg instance using the 750Ti using a custom script

The script is below

sudo strace Xorg :2 vt8 -config xorg-second.conf -configdir pwd/conf.d

I’ll attach the xorg-second.conf file shortly. The conf.d directory is empty, I’ve passed it to try and prevent other config files from being processed.

The result is that the monitor receives no signal via HDMI. More annoying, certain operations seem to hang the second Xorg instance. For example, running

xrandr --display :2

once works, but the second time it hangs.

The same setup works with Windows, I’ve booted a Windows 8.1 from an external drive and output is sent via both video cards.

What do I have to do to enable the second video card?



nvidia-bug-report.log.gz (214 KB)
xorg-second.conf.txt (1.22 KB)

Do you really plan to run two completely separate X servers on these cards? The traditional way to handle this is to have one X server with two X screens, one for each GPU. But most modern desktop environments really don’t like having more than one X screen, so you’ll probably want to turn on Xinerama to stitch them together into one logical X screen. That comes with its own caveats, of course.

If you really want to run two independent X servers, you’ll need to start them with the -sharevts option (and maybe -novtswitch), and disable the ProbeAllGpus option on both X servers. This is not a supported configuration though, so it’s not really expected to work.

Thanks for the reply Aaron, I’ll investigate the options you mentioned.

My end goal is VFIO passthrough, but since that did not seem to work I tried to double-check and see whether I was able to use both GPUs at the same time on Linux.