Backlight
This page documents methods for controlling backlight (aka screen brightness) and tips to control it via hotkeys.
Kernel native
Some laptops, using a recent enough kernel, will automatically handle increasing and decreasing the backlight using the hot keys. The following tools will allow scripting or controlling the backlight using other means, if desired.
Desktop Environment native
Some desktop environments will handle querying and setting the backlight, including configuring the backlight keys. These include at least: Plasma (KDE) and XFCE. It may be needed to configure or start some desktop environment-specific services.
xbacklight
xbacklight uses X to change the light settings. This can be inconvenient in some situations, e.g. for use with the services.actkbd service, which doesn't know about the X session. It, though, has an history of being more compatible with different hardware, especially newer hardware[citation needed]
To install xbacklight globally, add this to your configuration.nix.
environment.systemPackages = with pkgs; [ xorg.xbacklight ];
Alternatively, use nix-env -iA nixos.xorg.xbacklight to install it to your user profile.
light
light does not use X to change the light settings. This can be used in situations where the X service isn't available. While it does not use X, it will need some privileges to work.
To enable the use of light, add this to your configuration.nix and make sure that your user is a member of the video group.
programs.light.enable = true;
The following commands will allow you to test light:
light -U 30— the screen should become darker.light -A 30— the screen should become brighter.
Be careful using light -U, as you might turn your backlight completely off! You will not be able to see what you're typing anymore.
brightnessctl
brightnessctl (homepage) is another option, which, like light, would work even without X.
To enable it, set hardware.brightnessctl.enable to true, and ensure that the users which will use brightnessctl are members of the video group.
Tips
Key mapping
While controlling the backlight via the command line is useful, it would be preferable to control it using key bindings. This is especially true considering most laptops have backlight control keys.
There are two main choices to add key bindings, using a system-level service like actkbd or using an X session tool, either provided by your Desktop environment, Window manager or a tool like xbindkeys.
Depending on the tools that work for controlling the backlight you will be able to choose one of those options.
light
|
xbacklight
| |
| System service | Yes | With hacks |
| X session | Yes | Yes |
Follows, an example mapping for use with actkbd:
programs.light.enable = true;
services.actkbd = {
enable = true;
bindings = [
{ keys = [ 224 ]; events = [ "key" ]; command = "/run/current-system/sw/bin/light -A 10"; }
{ keys = [ 225 ]; events = [ "key" ]; command = "/run/current-system/sw/bin/light -U 10"; }
];
};