This was supported in the old dos version, through the 3 keyboard leds, but of course accessing these leds with a multitasking os can be more problematic and the emulation was just dropped when switching to the sdl version, a very long time ago... Now there are ways to access the leds available on the system in linux through sysfs. It makes accessing any led and controlling it much easier. These leds are available in /sys/class/leds, see the description in any kernel documentation in /usr/s