KDE

KDE Plasma is a desktop environment that aims to be simple by default, powerful when needed.

Installation

Plasma 6

/etc/nixos/configuration.nix

{
  services.xserver.enable = true; // optional
  services.displayManager.sddm.enable = true;
  services.displayManager.sddm.wayland.enable = true;
  services.desktopManager.plasma6.enable = true;
}

Plasma 5

/etc/nixos/configuration.nix

{
  services.xserver.enable = true;
  services.displayManager.sddm.enable = true;
  services.xserver.desktopManager.plasma5.enable = true;
}

Configuration

Rootless X11

sddm launches X11 as a root user by default. For better security, X11 can be run as a non-root user but using Wayland is preferred and better tested:

services.xserver.displayManager.sddm.settings.General.DisplayServer = "x11-user";

Excluding applications from the default install

Some optional packages can be excluded if they are not needed at the cost of functionality.

Plasma 6

Optional packages: plasma6.nix

environment.plasma6.excludePackages = with pkgs.kdePackages; [
  plasma-browser-integration
  konsole
  elisa
];

Plasma 5

Optional packages: plasma5.nix

environment.plasma5.excludePackages = with pkgs.libsForQt5; [
  plasma-browser-integration
  konsole
  oxygen
];

GNOME desktop integration

Using the following example configuration, QT applications will have a look similar to the GNOME desktop, using a dark theme.

qt = {
  enable = true;
  platformTheme = "gnome";
  style.name = "adwaita-dark";
};

For other themes, you may need the packages libsForQt5.qt5ct and libsForQt5.qtstyleplugin-kvantum and a symlink from ~/.config/Kvantum/ to your theme package. Here is an example using Arc-Dark and Home Manager. In the Home Manager configuration:

qt = {
  enable = true;
  platformTheme = "qtct";
  style.name = "kvantum";
};

xdg.configFile = {
  "Kvantum/ArcDark".source = "${pkgs.arc-kde-theme}/share/Kvantum/ArcDark";
  "Kvantum/kvantum.kvconfig".text = "[General]\ntheme=ArcDark";
};

For more details, see this forum post.

Default Wayland/X11 session

Plasma 5

Plasma 5 runs on X11 by default and it is recommend to use Plasma 6 for Wayland instead. To launch a Wayland session by default anyway:

services.xserver.displayManager.defaultSession = "plasmawayland";

Plasma 6

Plasma 6 runs on Wayland by default. To launch an X11 session by default:

services.xserver.displayManager.defaultSession = "plasmax11";

SDDM on Wayland

services.xserver.displayManager.sddm.wayland.enable = true;

Troubleshooting

Qt/KDE applications segfault on start

This is caused by a stale QML cache (see this issue). A dirty way to fix this is by running on a terminal the following command:

find ${XDG_CACHE_HOME:-$HOME/.cache}/**/qmlcache -type f -delete

GTK themes are not applied in Wayland applications / Window Decorations missing / Cursor looks different

This affects GTK applications including Firefox and Thunderbird.

If you are using Plasma 5, add to your configuration.nix the following line:

programs.dconf.enable = true;

You might also need to set a GTK theme Breeze imitating the KDE theme with the same name in System Settings -> Application Style -->Configure GNOME/GTK Application Style.

(See this issue)

Tips and tricks

Plasma-Manager

Note: Plasma-Manager is not matured yet and unofficial community project

By default, the Plasma configuration can be handled like on traditional systems. With plasma-manager, it is possible to make Plasma configurations via nix by providing home-manager modules.