Linux
Dead keyboard
If almost none of the keys on your keyboard seem to work when you start the emulation (only Return, but no Space, letters, or numbers), this may be a problem with Wayland. There seem to be problems between SDL (Simple DirectMedia Layer) and Wayland.
If you cannot run X11 on your desktop (many distributions have already removed the X11 desktop), put this setting in your script files:
export SDL_VIDEODRIVER=x11
This forces the SDL library to use the XWayland adapter. At least on my system, this restores the keyboard function in MAME.
