I've installed Ubuntu Studio Xenial 16.04.1 on my PC with i7 6800k and GTX 970, connected to my iMac 11,3 (which I'm using as a monitor) via DisplayPort.I'm not able to change the backlight levels of my display; in fact, my /sys/class/backlight is completely empty.

When I run lshw -c video, I get:

       description: VGA compatible controller
       product: GM204 [GeForce GTX 970]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:03:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller bus_master cap_list rom
       configuration: driver=nvidia latency=0
       resources: irq:53 memory:fa000000-faffffff memory:e0000000-efffffff memory:f0000000-f1ffffff ioport:e000(size=128) memory:fb000000-fb07ffff

If I open Software & Updates and go to the Additional Drivers tab, under the NVIDIA Corporation:GM204[GeForce GTX 970], is says I'm Using NVIDIA binary driver-version 367.57 from nvidia-367 (proprietary, tested).

For the device Unknown: Unknown, it says I'm Using Processor microcode firmware for Intel CPUs from intel-microcode(proprietary) instead of Do not use the device.

In case it helps, I've located the brightness and max_brightness files in another directory: /sys/devices/pci0000:00/0000:00:1c.3/0000:06:00.0/leds/phy0-led/

How can I setup my system so that I can change my iMac screen brightness using my apple keyboard shortcuts just as I can volume?

  • It is not possible to change backlight on the external device. Unless some special way to send commands through the Display port. I do not think there is an easy solution for that. – Pilot6 Jan 28 '17 at 21:15
  • Really? So everyone who uses external monitors have to use physical controls on the actual monitor, and can't change from within the OS? Even on Windows? I don't get how I can control my iMac's speaker volume levels through DisplayPort but not display backlight levels. – CPLTarun Jan 28 '17 at 21:19
  • Some monitor vendors provide some utilities to control the backlight of their monitors, some don't. There is no generic way to control backlight of external monitors. – Pilot6 Jan 28 '17 at 21:21
  • Well, that's a bummer :/. Does this mean my iMac display will be using full backlight levels (and draw full power) as long as it's in use by my pc? – CPLTarun Jan 28 '17 at 21:23
  • I think you can adjust it in your iMac. – Pilot6 Jan 28 '17 at 21:25

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