Module to control the brightness of the screen in linux environments

Requirements

This module assumes that the following files exists:

• /sys/class/backlight/intel_backlight/max_brightness
• /sys/class/backlight/intel_backlight/brightness

Also, brightness should be updatable by changing the content of /sys/class/backlight/intel_backlight/brightness.

Permissions

To use this module, the owner of the xmonad process will need to have permission to write to /sys/class/backlight/intel_backlight/brightness. To achieve this, you can:

• Create a group with your user and root and give permissions to this group to write to the file. I usually follow these steps:

  • Create a group named xmonad

  $ sudo groupadd xmonad

  • Add user root and your user name to the group xmonad.

  $ sudo usermod -a -G xmonad root
  $ sudo usermod -a -G xmonad sibi

  • The files under /sys are virtual. It's a RAM based filesystem through which you can access kernel data structures. The permission you give there won't persist after reboot. One of the way for persisting is creating a systemd script:

  $ cat /etc/systemd/system/brightness.service
  [Unit]
  Description=Set brightness writable to everybody
  Before=nodered.service
  
  [Service]
  Type=oneshot
  User=root
  ExecStart=/bin/bash -c "chgrp -R -H xmonad /sys/class/backlight/intel_backlight && chmod g+w /sys/class/backlight/intel_backlight/brightness"
  
  [Install]
  WantedBy=multi-user.target
  
  $ sudo systemctl enable brightness.service
  $ sudo systemctl start brightness.service
  $ sudo systemctl status brightness.service

• Allow anyone to write the file through 646 permissions: -rw-r--rw-;