sysbacklight is a tiny tool meant to be used on configurations where xbacklight does not work.
It changes the display brightness on the first sysfs backlight device of type raw.
It is written in C using libsysfs so it is possible to install it SUID-root.
sysbacklight is free software under the GNU AGPL version 3. See LICENSE for details.
sysbacklight needs libsysfs.
On Debian, you can install them with:
# apt install libsysfs-dev
sysbacklight or sysbacklight ?
sysbacklight = 42
sysbacklight + 10
sysbacklight - 10