kb-layout-daemon

A lightweight daemon that automatically switches keyboard layout based on which physical keyboard you're typing on.

Perfect for users with multiple keyboards who want different layouts for each (e.g., English on one keyboard, German on another).

Features

• Monitors multiple keyboards simultaneously
• Two modes:
  • Grab mode: Correct layout on first keystroke (~1ms latency)
  • Passive mode: Zero latency (first key after switch may use old layout)
• Toggle between modes via D-Bus or KDE Plasma widget
• Native D-Bus integration with KDE Plasma
• Minimal resource usage (~2MB RAM, <1% CPU)
• Single static binary, no runtime dependencies
• Configurable via TOML file
• Systemd user service included
• KDE Plasma widget to toggle modes (KDE Store)

Requirements

• Linux with evdev support
• KDE Plasma (Wayland or X11)
• User must be in the input group

Installation

From source

git clone https://github.com/aydiler/kb-layout-daemon
cd kb-layout-daemon
cargo build --release
sudo cp target/release/kb-layout-daemon /usr/local/bin/

Arch Linux (AUR)

yay -S kb-layout-daemon-git

From crates.io

cargo install kb-layout-daemon

Setup

1. Add yourself to the input group:

   sudo usermod -aG input $USER

   Then log out and back in.

2. Create config file at ~/.config/kb-layout-daemon/config.toml:

   # Mode: "grab" (correct first key) or "passive" (zero latency)
   mode = "grab"
   
   [[keyboards]]
   name = "Lofree"
   layout_index = 1
   layout_name = "English (US)"
   
   [[keyboards]]
   name = "CHERRY"
   layout_index = 0
   layout_name = "German"

   The layout_index corresponds to the order in KDE's keyboard layout settings (0-based).

3. Install the systemd service:

   mkdir -p ~/.config/systemd/user
   cp kb-layout-daemon.service ~/.config/systemd/user/
   systemctl --user enable --now kb-layout-daemon

KDE Plasma Widget

A panel widget is included to toggle between Grab and Passive modes.

Install from KDE Store

KB Layout Mode Toggle on KDE Store

Or install manually:

cp -r widget ~/.local/share/plasma/plasmoids/org.kblayout.toggle

Then right-click your panel → "Add Widgets" → search for "KB Layout Mode" → drag to panel.

• Green "KB": Grab mode (correct first key, ~1ms latency)
• Red "GM": Passive/Game mode (zero latency)

Click to toggle between modes.

D-Bus Interface

Control the daemon via D-Bus at org.kblayout.Daemon:

# Get current mode
dbus-send --session --print-reply --dest=org.kblayout.Daemon \
  /org/kblayout/Daemon org.kblayout.Daemon.GetMode

# Set mode
dbus-send --session --print-reply --dest=org.kblayout.Daemon \
  /org/kblayout/Daemon org.kblayout.Daemon.SetMode string:"passive"

# Toggle mode
dbus-send --session --print-reply --dest=org.kblayout.Daemon \
  /org/kblayout/Daemon org.kblayout.Daemon.ToggleMode

Configuration

The config file uses TOML format:

Field	Description
mode	Initial mode: "grab" or "passive" (default: "grab")

Each [[keyboards]] section defines a keyboard to monitor:

Field	Description
name	Substring to match in the device name (case-insensitive)
layout_index	KDE layout index (0-based, matches order in System Settings)
layout_name	Human-readable name for logging

To find your keyboard names:

cat /proc/bus/input/devices | grep -A 4 "Name="

How It Works

1. On startup, scans /dev/input/event* for keyboards matching configured names
2. Monitors all keyboards using evdev
3. On keypress, checks if layout switch is needed
4. Switches layout via D-Bus call to org.kde.keyboard

Grab mode: Grabs exclusive access to keyboards, intercepts all input, switches layout, then forwards events through a virtual keyboard. This ensures the first keystroke uses the correct layout.

Passive mode: Monitors keyboards without grabbing. Layout switches after detecting a keypress, so the first key may use the old layout. Zero added latency.

Troubleshooting

"No keyboards found"

• Ensure you're in the input group: groups | grep input
• Log out and back in after adding yourself to the group

Layout not switching

• Check KDE has multiple layouts configured
• Verify layout_index matches your KDE layout order
• Check logs: journalctl --user -u kb-layout-daemon -f

Keys not working in Grab mode

• Try switching to Passive mode: dbus-send --session --print-reply --dest=org.kblayout.Daemon /org/kblayout/Daemon org.kblayout.Daemon.SetMode string:"passive"
• Report the issue with your keyboard model

License

MIT