Automatic Dark/Light Theme Switching on Sway with Guix

I’ve been meaning to set up automatic theme switching for a while now. Manually toggling between dark and light themes gets old fast, especially when I’m working across different times of day. Enter darkman - a simple daemon that handles this automatically.

What is Darkman?

Darkman is a framework for dark-mode and light-mode transitions. It automatically switches themes at sunrise and sunset based on your location, and lets you manually toggle when needed. The beauty is in its simplicity: it runs scripts when switching modes, so you can control exactly what changes.

Guix Home Setup

On Guix, darkman integrates via a home service. Add this to your home configuration:

(service home-darkman-service-type
         (home-darkman-configuration
          (latitude 38.7)
          (longitude -9.2)
          (use-geoclue? #f)))

Set your latitude and longitude to get accurate sunrise/sunset times. I disable geoclue since I don’t need dynamic location tracking.

What Gets Switched

Darkman will handle:

• GTK applications: LibreOffice, Thunar, file managers (Yaru-dark ↔ Yaru theme)
• Foot terminal: Instant color switching via UNIX signals
• Dunst notifications: Background and foreground colors

The Implementation

Darkman executes scripts from two directories:

• ~/.local/share/dark-mode.d/ - runs when switching to dark mode
• ~/.local/share/light-mode.d/ - runs when switching to light mode

For GTK apps, two separate mechanisms are needed - not all applications respect both:

1. Portal/D-Bus (for modern apps)

gsettings set org.gnome.desktop.interface color-scheme 'prefer-dark'
gsettings set org.gnome.desktop.interface gtk-theme 'Yaru-dark'

The color-scheme setting broadcasts via D-Bus to the FreeDesktop portal (org.freedesktop.appearance.color-scheme). Modern applications - Firefox, Chrome, VSCode, Electron apps - listen to this portal and switch automatically.

The gtk-theme setting tells GTK applications which theme to use (e.g., Yaru-dark vs Yaru). For light mode, use prefer-light and remove the -dark suffix from the theme name.

2. GTK-3 settings.ini (for legacy apps)

Some applications like Thunar read ~/.config/gtk-3.0/settings.ini directly instead of using D-Bus:

[Settings]
gtk-theme-name = Yaru-dark
gtk-application-prefer-dark-theme = 1

The darkman script copies a template to this location:

TEMPLATE="$HOME/.local/share/gtk-themes/settings-dark.ini"
GTK3_CONFIG="$HOME/.config/gtk-3.0/settings.ini"
cp "$TEMPLATE" "$GTK3_CONFIG"

For light mode, set gtk-theme-name = Yaru and gtk-application-prefer-dark-theme = 0.

For the Foot terminal I run foot --server and connect with footclient. This lets me use signals for instant theme switching - one signal updates the server and all connected terminals without restart:

# Dark mode: SIGUSR1 switches to [colors] section
kill -SIGUSR1 $(pgrep -x foot) 2>/dev/null || true

# Light mode: SIGUSR2 switches to [colors2] section
kill -SIGUSR2 $(pgrep -x foot) 2>/dev/null || true

Your foot.ini just needs both color sections defined, with initial-color-theme=1 to start dark.

Usage

Once configured, darkman runs automatically:

• Switches to light mode at sunrise
• Switches to dark mode at sunset
• Manual toggle with darkman toggle (I bind this to Mod+T in Sway)

Test it works:

darkman toggle

Everything should switch instantly - GTK apps, terminal colors, notifications.

Full Implementation

The complete setup with all scripts and configurations is in my dotfiles repository.