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Linux: keyboard doesn't work without display manager (Gnome/KDE) but everything else is fine

Running on Linux (CentOS/RedHat). Our use case is a kiosk, so I want to minimize installed packages. I assumed running X should be sufficient, without having to run Gnome or KDE.
For testing, I’m using “Platformer Game” from https://wiki.unrealengine.com/Linux_Demos
Running the game from Gnome or KDE – everything is fine.
Running the game without a display manager, after simply starting an X session – everything works (including mouse) except the keyboard.
What gives? This doesn’t make sense. How do I get the keyboard working without Gnome/KDE/twm/etc.?

First of, I would suggest running UE4 in unbuntu. Also I do believe it requires the GUI to run. And if it doesn’t require it, then I suggest asking this on the answerhub in the Linux section.

My guess would be that you are missing a xorg input configuration for your keyboard, or it is not configured correctly. There shouldn’t be any reason it would not work. You probably just have to go the extra mile to set up all the configuration yourself since you are not using a display manager. You might consider using something lightweight instead, to save yourself the headache, such as i3 (i3wm.org).

Thanks, will do.

I thought that such configuration is done by the X startup scripts, not the display manager. But this is what I see: startx script looks at the user .xinitrc, if any, otherwise uses the system default xinitrc. The system default xinitrc, in turn, checks user .Xlaunch files, if any, else uses the system defalt Xlaunch, in order to determine which programs to have running at the start of your X session. In the system Xlaunch, I see that it checks whether Gnome and/or KDE are present, and runs one of those; if not, it falls back to twm with xterm and the clock – nothing about keyboards. Also, it looks like installing the NVIDIA driver only rewrites the xorg.conf files and doesn’t touch these others.
The other thing is, that if I launch another X program, such as xterm, without a display manager, it works fine. I can type in xterm, and it receives and loses focus when I move the mouse in and out of its area. Now, I don’t know if there’s something special about the way UE4 connects to the keyboard that’s different – it seems to me that must be the case, as I don’t see any other possibilities.

You can use xev to monitor a specific window, in this case the UE4 window to see where or if the X window events are even reaching the game window.

http://linux.die.net/man/1/xev