The internal display is the master. Brightness keys change the internal panel, show a compact OSD, and a user service mirrors the same percentage to the external monitor with ddcutil.

This avoids drift from letting two outputs auto-adjust independently.

Features

Internal display controlled with brightnessctl
External monitor mirrored with ddcutil VCP code 10
Compact GTK4/libadwaita OSD for custom brightness shortcuts
Optional Wayland top-edge positioning with gtk4-layer-shell
systemd user service for continuous external sync
Configurable backlight device, DDC bus, monitor model, step size, and sync interval
Optional wluma config where only the internal display is managed

Tested Setup

Fedora 43
GNOME Shell 49
Internal panel: intel_backlight
External monitor: DDC/CI via ddcutil

Other Fedora/GNOME setups should work if brightnessctl and ddcutil can control the displays.

Dependencies

sudo dnf install -y brightnessctl ddcutil python3-gobject gtk4 libadwaita gtk4-layer-shell

gtk4-layer-shell is recommended on GNOME Wayland. Without it, GNOME may place the OSD like a normal GTK window instead of pinning it at the top edge.

If your ddcutil command needs sudo, configure passwordless sudo for the specific command you use. Example:

jan ALL=(root) NOPASSWD: /usr/bin/ddcutil

Use a stricter sudoers rule if you prefer limiting arguments.

Quick Install

git clone https://gitea.diehanis.de/Jan/Fedora_Brightness_Automation_Buttons_OSD.git
cd Fedora_Brightness_Automation_Buttons_OSD
./install.sh

The installer writes:

~/.local/bin/brightness-osd
~/.local/bin/brightness-up-all
~/.local/bin/brightness-down-all
~/.local/bin/brightness-sync-hg342pcb
~/.config/systemd/user/external-brightness-sync.service
~/.config/brightness-automation/env

Then set your GNOME custom keyboard shortcuts to:

/home/YOUR_USER/.local/bin/brightness-down-all
/home/YOUR_USER/.local/bin/brightness-up-all

Use the full path in GNOME Settings.

Configuration

Edit:

~/.config/brightness-automation/env

Default config:

BRIGHTNESS_BACKLIGHT_DEVICE="intel_backlight"
BRIGHTNESS_SYNC_BACKLIGHT="/sys/class/backlight/intel_backlight"
BRIGHTNESS_STEP="10"
BRIGHTNESS_DDCUTIL_MODEL="HG342PCB"
BRIGHTNESS_DDCUTIL_DISPLAY="1"
BRIGHTNESS_DDCUTIL_BUS="16"
BRIGHTNESS_SYNC_INTERVAL="1"
BRIGHTNESS_SYNC_MIN_PERCENT="1"
BRIGHTNESS_OSD_VISIBLE_MS="1400"

After changing DDC or sync values:

systemctl --user restart external-brightness-sync.service

Finding Your Values

Backlight device:

brightnessctl -l
ls /sys/class/backlight

External monitor:

sudo ddcutil detect
sudo ddcutil getvcp 10

If ddcutil detect reports a bus like /dev/i2c-16, set:

BRIGHTNESS_DDCUTIL_BUS="16"

wluma

If you use wluma, let it manage only the internal display. The external monitor should follow through the sync service.

Optional install of the example wluma config:

INSTALL_WLUMA_CONFIG=1 ./install.sh
systemctl --user restart wluma.service

Example config is in:

wluma/config.toml

Status

systemctl --user status external-brightness-sync.service
journalctl --user -u external-brightness-sync.service -n 50 --no-pager

Design Notes

Implementation decisions and failed attempts are documented in:

docs/implementation-log.md

Uninstall

./uninstall.sh

The uninstall script keeps ~/.config/brightness-automation/env so local settings are not destroyed.