Setting the keyboard backlight to turn off and on based on the idle trigger and a time delay

Table of Contents

• Setting the keyboard backlight to turn off and on based on the idle trigger and a time delay
  • Overview
  • 1. Install xidlehook
  • 2. Create a service that only changes the permission on the file /sys/class/leds/tpacpi::kbd_backlight/brightness
  • 3. Copy the other files from repo into their correct locations (relative to home)

Overview

The below gives you an approach to set a timer to turn off the keyboard back light from when you have last touched the input devices (touchpad/keyboard/mouse). The keyboard back light will then return to its original state when coming out of idle mode.

This approach below works for thinkpads - I suspect this will work on non-Thinkpads too - with this line changed to whatever works for other products. /sys/class/leds/tpacpi::kbd_backlight/brightness

• I had to write in some logic to check kb backlight state and provide behaviour accordingly.
• I also had to work around some weird parse error when trying to run xidlehook from a systemd service

Five things needed to do this

1. Install xidlehook
2. Create a service that only changes the permission on the file /sys/class/leds/tpacpi::kbd_backlight/brightness
3. Create a /home/[YOUR_HOME_DIRECTORY]/.config/autostart file to execute the xidlehook command on boot and login
4. Create a script to run on idle and a cancel script to run when idle cancels in /home/[YOUR_HOME_DIRECTORY]/bin
5. Create a file to hold the original state of the kb-backlight /home/[YOUR_HOME_DIRECTORY]/.backlight_state

• Keep in mind when copying the scripts below that depending on the language and environment it can help reduce weird bugs to have a spare line at the end of each file.

Once you following the instructions you will have five new files as below (swap out my name for your home directory name)

• /etc/systemd/system/brightness-kb-backlight-permission.service
• /home/[YOUR_HOME_DIRECTORY]/.config/autostart/kb_brightness.desktop
• /home/[YOUR_HOME_DIRECTORY]/bin/run_dim_check.sh
• /home/[YOUR_HOME_DIRECTORY]/bin/run_dim_check_cancel.sh
• /home/[YOUR_HOME_DIRECTORY]/.backlight_state

1. Install xidlehook

​For archlinux

paru -S xidlehook

You can test it by trying this command

sudo xidlehook --timer 3 'echo 0 | tee /sys/class/leds/tpacpi::kbd_backlight/brightness' 'echo 1 | tee /sys/class/leds/tpacpi::kbd_backlight/brightness'

2. Create a service that only changes the permission on the file /sys/class/leds/tpacpi::kbd_backlight/brightness

Linux resets the permission on this file on each reboot - so this gets the permission back to a permissions state where we can write to the file without needing sudo

Copy the script into /etc/systemd/system/brightness-kb-backlight-permission.service

Once it is copied do the following to make sure the service is registered

➜ sudo systemctl daemon-reload

~ 
➜ sudo systemctl enable brightness-kb-backlight-permission.service

~ 
➜ sudo systemctl start brightness-kb-backlight-permission.service

~ 
➜ sudo systemctl status brightness-kb-backlight-permission.service
○ brightness-kb-backlight-permission.service - Change permission for kb backlight file for use without sudo with xidlehook
     Loaded: loaded (/etc/systemd/system/brightness-kb-backlight-permission.service; enabled; vendor preset: disabled)
     Active: inactive (dead) since Thu 2021-05-27 11:27:53 NZST; 24min ago
    Process: 21032 ExecStart=/usr/bin/chmod 777 /sys/class/leds/tpacpi::kbd_backlight/brightness (code=exited, status=0/SUCCESS)
   Main PID: 21032 (code=exited, status=0/SUCCESS)
        CPU: 1ms

May 27 11:27:53 arch-t460p systemd[1]: Started Change permission for kb backlight file for use without sudo with xidlehook.
May 27 11:27:53 arch-t460p systemd[1]: brightness-kb-backlight-permission.service: Deactivated successfully.

3. Copy the other files from repo into their correct locations (relative to home)

• /home/[YOUR_HOME_DIRECTORY]/.config/autostart/kb_brightness.desktop
• /home/[YOUR_HOME_DIRECTORY]/bin/run_dim_check.sh
• /home/[YOUR_HOME_DIRECTORY]/bin/run_dim_check_cancel.sh
• /home/[YOUR_HOME_DIRECTORY]/.backlight_state