#keyboard #backlight #laptop #thinkpad

app keyboard-backlightd

Keyboard backlight timeout daemon for laptops

10 releases

0.1.9 Apr 2, 2024
0.1.8 Feb 9, 2024
0.1.7 Oct 21, 2023
0.1.5 Apr 27, 2023
0.1.1 Feb 19, 2023

#130 in Hardware support


461 lines


[ crates.io ] [ lib.rs ] [ AUR ]

A daemon to turn off the keyboard backlight when idle.


  • Small, minimal dependencies, fast to compile.
  • Supports adjusting the keyboard backlight using the normal key (by monitoring if brightness was changed by hardware and adjusting accordingly).


  • Only tested on modern ThinkPads.
  • Very little auto-detection, you will need to configure your input devices
  • Linux only. Uses some very low level APIs.


While this package can be built with cargo as most rust packages, it uses make for installation. This is because cargo is not able to install the additional files that are needed: The config file and the systemd unit file.

Why is this needed? Since this is a system daemon it needs to be installed system-wide and run as root (to be able to access certain files in /dev and /sys).

Thus you should ideally install this with your distro package manager. A package for Arch Linux is available on AUR (maintained by the author of this package).

If you do not use Arch Linux, I would appreciate if you can contribute creating a package! However, if you do not want to create a package, do something like this to install into /usr/local:

$ # NOTE! Not recommended! This will overwrite your config file for this
$ # program, which sucks if you customised it. Use your package manager
$ # instead!
$ make
$ sudo make install


This program will monitor your key presses, but only to detect when you press the keys. It does however not care about what you press. The only thing the code checks is if it is a LED changing state, in which case it is ignored (otherwise, pressing Caps Lock on an external keyboard would light up the keyboard backlight).

In summary: This code works very similar to how a keylogger would, except that it is benign. But you should read the code first to make sure you trust me with this! (This is a good idea in general!)

The code that does this is in handlers.rs in the mod ev_dev section.

Figuring out input devices & LEDs

You probably want this daemon to turn on the keyboard backlight on any of:

  • Keyboard keys
  • Special Fn-key combos?
  • Touchpad
  • Trackpoint

The easiest way is to run sudo evtest (you may need to install a package such as evtest). This will give you an output such as this:

$ sudo evtest
No device specified, trying to scan all of /dev/input/event*
Available devices:
/dev/input/event0:	Sleep Button
/dev/input/event1:	Lid Switch
/dev/input/event10:	ThinkPad Extra Buttons
/dev/input/event11:	HDA Intel PCH Mic
/dev/input/event12:	HDA Intel PCH Headphone
/dev/input/event13:	HDA Intel PCH HDMI/DP,pcm=3
/dev/input/event14:	HDA Intel PCH HDMI/DP,pcm=7
/dev/input/event15:	HDA Intel PCH HDMI/DP,pcm=8
/dev/input/event16:	Synaptics TM3276-022
/dev/input/event17:	TPPS/2 IBM TrackPoint
/dev/input/event18:	Integrated Camera: Integrated C
/dev/input/event19:	MX Vertical Mouse
/dev/input/event2:	Power Button
/dev/input/event3:	AT Translated Set 2 keyboard
/dev/input/event4:	Video Bus
/dev/input/event5:	Video Bus
/dev/input/event6:	Microsoft Comfort Curve Keyboard 3000
/dev/input/event7:	Microsoft Comfort Curve Keyboard 3000
/dev/input/event8:	Raydium Corporation Raydium Touch System
/dev/input/event9:	PC Speaker
Select the device event number [0-19]:

This lets you identify the input devices Linux sees. However, this is not quite what you want, as the numbering is not guaranteed to be stable across reboots.

Next you need to find a stable ID for these:

$ ls -l /dev/input/by-id                                
lrwxrwxrwx 1 root root  9  7 feb 16.31 usb-Microsoft_Comfort_Curve_Keyboard_3000-event-kbd -> ../event6
lrwxrwxrwx 1 root root  9  7 feb 16.31 usb-Microsoft_Comfort_Curve_Keyboard_3000-if01-event-kbd -> ../event7
lrwxrwxrwx 1 root root  9  7 feb 16.31 usb-Raydium_Corporation_Raydium_Touch_System-event-if00 -> ../event8
lrwxrwxrwx 1 root root 10  7 feb 16.31 usb-SunplusIT_Inc_Integrated_Camera-event-if00 -> ../event18
$ ls -l /dev/input/by-path
lrwxrwxrwx 1 root root  9  7 feb 16.31 pci-0000:00:14.0-usb-0:10:1.0-event -> ../event8
lrwxrwxrwx 1 root root  9  7 feb 16.31 pci-0000:00:14.0-usb-0:1:1.0-event-kbd -> ../event6
lrwxrwxrwx 1 root root  9  7 feb 16.31 pci-0000:00:14.0-usb-0:1:1.1-event-kbd -> ../event7
lrwxrwxrwx 1 root root 10  7 feb 16.31 pci-0000:00:14.0-usb-0:8:1.0-event -> ../event18
lrwxrwxrwx 1 root root 10  7 feb 16.31 pci-0000:00:1f.4-event-mouse -> ../event16
lrwxrwxrwx 1 root root  9  7 feb 16.31 pci-0000:00:1f.4-mouse -> ../mouse1
lrwxrwxrwx 1 root root 10  7 feb 16.31 pci-0000:00:1f.4-serio-2-event-mouse -> ../event17
lrwxrwxrwx 1 root root  9  7 feb 16.31 pci-0000:00:1f.4-serio-2-mouse -> ../mouse2
lrwxrwxrwx 1 root root  9  7 feb 16.31 platform-i8042-serio-0-event-kbd -> ../event3
lrwxrwxrwx 1 root root  9  7 feb 16.31 platform-pcspkr-event-spkr -> ../event9
lrwxrwxrwx 1 root root 10  7 feb 16.31 platform-thinkpad_acpi-event -> ../event10

Here you should prefer a by-id mapping if one exists for your device, though for non-USB devices by-path will likely work fine.

From the output above we can conclude that we want:

Device Human readable name Number Path we want
Keyboard AT Translated Set 2 keyboard 3 /dev/input/by-path/platform-i8042-serio-0-event-kbd
Special buttons ThinkPad Extra Buttons 10 /dev/input/by-path/platform-thinkpad_acpi-event
Touchpad Synaptics TM3276-022 16 /dev/input/by-path/pci-0000:00:1f.4-event-mouse
Trackpoint TPPS/2 IBM TrackPoint 17 /dev/input/by-path/pci-0000:00:1f.4-serio-2-event-mouse
Touchscreen Raydium Corporation Raydium Touch System 8 /dev/input/by-id/usb-Raydium_Corporation_Raydium_Touch_System-event-if00

These are (for this laptop, a ThinkPad T480) all the inputs we want to monitor.

Here are some hints for figuring this out:

  • The two most common vendors I have seen for touchpads are Synaptics and ALPS.
  • You can always use evtest to check if key presses go to a specific device.

Thus, our command line for keyboard-backlightd would look like:

-i /dev/input/by-path/platform-i8042-serio-0-event-kbd \
-i /dev/input/by-path/platform-thinkpad_acpi-event \
-i /dev/input/by-path/pci-0000:00:1f.4-event-mouse \
-i /dev/input/by-path/pci-0000:00:1f.4-serio-2-event-mouse \
-i /dev/input/by-id/usb-Raydium_Corporation_Raydium_Touch_System-event-if00

Then you also need to figure out the path to your LED for keyboard backlight. This is thankfully much easier:

$ ls -d /sys/class/leds/*kbd*

In this case there was only one option. This means we want:

-l /sys/class/leds/tpacpi::kbd_backlight


Once you have found your required command line parameters, edit /etc/conf.d/keyboard-backlightd to set them for use in the systemd service.

Then enable and start the systemd service and make sure everything still works:

$ systemctl enable keyboard-backlightd
$ systemctl start keyboard-backlightd

If you have issues with the service not starting during boot, consider increasing WAIT in the configuration file. This might help with late loaded kernel modules causing the device node to not be available when the daemon starts.


The keyboard backlight stops turning on if I hit the key that manually controls the backlight

This is by design. The daemon monitors (on supported laptops) for external changes to the keyboard backlight. That could be other software or the user pressing some laptop specific key combo (often involving the Fn key). On modern Thinkpads (2020-ish) this key combo is Fn+Space which cycles between "off", "half" and "bright".

keyboard-backlightd will adapt to what the user sets and toggle between "off" and whatever brightness level the user just set. If you happen to set it to off, that means you will get toggling between "off" and "off". Just hit the key combo again to resume operation at the next level of brightness.

If you really don't want this, you can use the flag --no-adaptive-brightness to the daemon. But consider giving it a try first, you might grow to like it.

Minimum supported rust version (MSRV)

Currently at least Rust 1.71.0 is needed, but this may change at any time if needed. MSRV change is not considered a breaking change and as such may change even in a patch version.


keyboard-backlightd is released under GPL 3.0 (only, not "or later").


~128K SLoC