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COSMIC Desktop Environment Skill

cosmic-deolafkfreund
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Updated 2/6/2026

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SKILL.md

COSMIC Desktop Environment Skill

Expert guidance for System76's COSMIC Desktop on NixOS Rust-based desktop environment with modern Wayland compositor

Overview

COSMIC (Computer Operating System Main Interface Components) is System76's next-generation desktop environment written entirely in Rust. Built using the iced cross-platform GUI library and Smithay compositor framework, COSMIC provides a modern, performant, and customizable desktop experience on NixOS.

Key Features:

  • Rust-based: Memory-safe, high-performance implementation
  • Wayland-native: Modern compositor (cosmic-comp) built on Smithay
  • Tiling & Floating: Flexible workspace management
  • RON Configuration: Rusty Object Notation for settings
  • Modular Architecture: Component-based design
  • Active Development: Regular updates from System76

NixOS Status:

  • Native support since NixOS 25.05 (Alpha 7)
  • Beta support in NixOS 25.11+
  • Flake available for cutting-edge versions
  • Binary cache available for faster builds

Installation

Method 1: Native NixOS (25.05+)

Basic Setup (NixOS 25.05 and later):

# configuration.nix
{
  # Enable COSMIC Desktop
  services.desktopManager.cosmic.enable = true;

  # Enable COSMIC Greeter (login manager)
  services.displayManager.cosmic-greeter.enable = true;
}

Minimal Installation (exclude unwanted apps in NixOS 25.11+):

{
  services.desktopManager.cosmic.enable = true;
  services.displayManager.cosmic-greeter.enable = true;

  # Exclude specific COSMIC applications
  environment.cosmic.excludePackages = with pkgs; [
    cosmic-edit      # Text editor
    cosmic-term      # Terminal emulator
    cosmic-files     # File manager
    # Add other packages to exclude
  ];
}

Method 2: Flake-Based (Cutting-Edge)

For Latest Development Versions:

Create /etc/nixos/flake.nix:

{
  description = "NixOS configuration with COSMIC Desktop";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

    # COSMIC flake (follows specific nixpkgs)
    nixos-cosmic = {
      url = "github:lilyinstarlight/nixos-cosmic";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = { self, nixpkgs, nixos-cosmic, ... }: {
    nixosConfigurations.hostname = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";

      modules = [
        # Enable binary cache FIRST
        {
          nix.settings = {
            substituters = [ "https://cosmic.cachix.org/" ];
            trusted-public-keys = [
              "cosmic.cachix.org-1:Dya9IyXD4xdBehWjrkPv6rtxpmMdRel02smYzA85dPE="
            ];
          };
        }

        # Import COSMIC module
        nixos-cosmic.nixosModules.default

        # Your configuration
        ./configuration.nix
      ];
    };
  };
}

Important: Run nixos-rebuild test FIRST to set up binary substituters before adding COSMIC packages.

Build Requirements:

  • RAM: ~16 GiB (reduce with --cores 1)
  • Disk: ~40 GiB for local builds
  • Binary cache available for nixos-unstable and nixos-24.11

Method 3: Home Manager Integration

COSMIC can be managed via Home Manager for user-specific configurations:

# home.nix
{ config, pkgs, ... }:
{
  # Install COSMIC applications
  home.packages = with pkgs; [
    cosmic-edit
    cosmic-term
    cosmic-files
    cosmic-store
  ];

  # Manage COSMIC config files declaratively
  xdg.configFile = {
    # Panel configuration
    "cosmic/com.system76.CosmicPanel.Panel/v1/name".text = "Panel";

    # Applets configuration (example)
    "cosmic/com.system76.CosmicPanel.Panel/v1/plugins_center".text = ''
      (
        entries: [
          CosmicAppletTime,
          CosmicAppletNotifications,
        ],
      )
    '';

    # Compositor settings
    "cosmic/com.system76.CosmicComp/v1/xkb_config".text = ''
      (
        rules: "",
        model: "",
        layout: "us",
        variant: "",
        options: Some("caps:escape"),
      )
    '';
  };
}

Configuration Structure

Configuration File Hierarchy

COSMIC uses RON (Rusty Object Notation) files for configuration:

~/.config/cosmic/
├── com.system76.CosmicPanel.Panel/
│   ├── v1/
│   │   ├── name              # Panel name
│   │   ├── plugins_wings     # Left/right applets
│   │   ├── plugins_center    # Center applets
│   │   └── output            # Display output
│   └── v2/                   # Future version
├── com.system76.CosmicComp/
│   └── v1/
│       ├── xkb_config        # Keyboard layout
│       ├── workspaces        # Workspace config
│       └── autotile          # Tiling settings
├── com.system76.CosmicSettings/
│   └── v1/
│       └── ...               # Desktop settings
└── com.system76.CosmicAppletTime/
    └── v1/
        └── ...               # Applet-specific settings

Key Characteristics:

  • System-wide: /run/current-system/sw/share/cosmic/ (NixOS defaults)
  • User-specific: ~/.config/cosmic/ (overrides system defaults)
  • RON Format: Rust Object Notation (similar to JSON)
  • Versioned: Each component uses versioned directories (v1, v2, etc.)

RON Configuration Examples

Panel Applet Configuration:

// ~/.config/cosmic/com.system76.CosmicPanel.Panel/v1/plugins_wings
(
  entries: [
    (
      applet: CosmicAppletWorkspaces,
      config: (
        workspace_mode: Fixed(4),
      ),
    ),
    CosmicAppletLauncher,
    CosmicAppletAudio,
    CosmicAppletNetwork,
    CosmicAppletBattery,
    CosmicAppletTime,
    CosmicAppletNotifications,
  ],
)

Compositor Configuration:

// ~/.config/cosmic/com.system76.CosmicComp/v1/autotile
(
  enabled: true,
  behavior: Global,
  gap: 8,
)

Keyboard Layout:

// ~/.config/cosmic/com.system76.CosmicComp/v1/xkb_config
(
  rules: "",
  model: "pc105",
  layout: "us",
  variant: "",
  options: Some("caps:escape,compose:ralt"),
)

Essential Configuration

Auto-Login

{
  services.displayManager.autoLogin = {
    enable = true;
    user = "username";
  };
}

Performance Optimization

Enable System76 Scheduler (recommended):

{
  # Improves system responsiveness and performance
  services.system76-scheduler.enable = true;

  # Optional: Configure scheduler settings
  services.system76-scheduler.settings = {
    cfsProfiles.enable = true;
    processScheduler.foregroundBoost.enable = true;
  };
}

Clipboard Management

Enable Clipboard Protocol (required for some apps):

{
  # Override Wayland security restrictions for clipboard
  environment.sessionVariables.COSMIC_DATA_CONTROL_ENABLED = "1";
}

Flatpak Support

For COSMIC Store and Flatpak Applications:

{
  services.flatpak.enable = true;
}

Then add Flathub as a user:

flatpak remote-add --user flathub https://dl.flathub.org/repo/flathub.flatpakrepo

Firefox Integration

Fix Firefox Theming (disable libadwaita interference):

{
  programs.firefox = {
    enable = true;
    preferences = {
      # Prevent GTK4/libadwaita from overriding COSMIC theme
      "widget.gtk.libadwaita-colors.enabled" = false;
    };
  };
}

Declarative Configuration with Home Manager

Complete Panel Configuration

{ config, pkgs, lib, ... }:
{
  xdg.configFile = {
    # Panel name and basic config
    "cosmic/com.system76.CosmicPanel.Panel/v1/name".text = "Panel";
    "cosmic/com.system76.CosmicPanel.Panel/v1/output".text = ''"All"'';
    "cosmic/com.system76.CosmicPanel.Panel/v1/anchor".text = "Bottom";
    "cosmic/com.system76.CosmicPanel.Panel/v1/size".text = "S";

    # Left/right applets
    "cosmic/com.system76.CosmicPanel.Panel/v1/plugins_wings".text = ''
      (
        entries: [
          CosmicAppletWorkspaces,
          CosmicAppletApplications,
          CosmicAppletAudio,
          CosmicAppletNetwork,
          CosmicAppletBattery,
          CosmicAppletTime,
          CosmicAppletNotifications,
          CosmicAppletPower,
        ],
      )
    '';

    # Center applets (optional)
    "cosmic/com.system76.CosmicPanel.Panel/v1/plugins_center".text = ''
      (
        entries: [],
      )
    '';
  };
}

Compositor Settings

{
  xdg.configFile = {
    # Auto-tiling configuration
    "cosmic/com.system76.CosmicComp/v1/autotile".text = ''
      (
        enabled: true,
        behavior: Global,
        gap: 8,
      )
    '';

    # Workspace configuration
    "cosmic/com.system76.CosmicComp/v1/workspaces".text = ''
      (
        workspace_mode: OutputBound,
        workspace_layout: Horizontal,
      )
    '';

    # Keyboard layout
    "cosmic/com.system76.CosmicComp/v1/xkb_config".text = ''
      (
        rules: "",
        model: "pc105",
        layout: "us,ru",
        variant: "",
        options: Some("grp:alt_shift_toggle,caps:escape"),
      )
    '';
  };
}

Application Theming

{
  xdg.configFile = {
    # Dark mode preference
    "cosmic/com.system76.CosmicTheme.Dark/v1/".text = ''
      (
        base: (
          palette: Dark,
          neutral_tint: None,
        ),
      )
    '';

    # Light mode preference
    "cosmic/com.system76.CosmicTheme.Light/v1/".text = ''
      (
        base: (
          palette: Light,
          neutral_tint: None,
        ),
      )
    '';
  };
}

Theming and Customization

Current Theming Status

Stylix Integration: Not yet available (tracked in issue #265)

Current Approach: Manual theme configuration via RON files

Manual Theme Configuration

Dark Theme Example:

{
  xdg.configFile."cosmic/com.system76.CosmicTheme.Dark/v1/".text = ''
    (
      base: (
        palette: Dark,
        neutral_tint: Some(Rgb(0.2, 0.3, 0.4)),
        accent: Rgb(0.5, 0.7, 1.0),
      ),
      spacing: Comfortable,
      corner_radii: Round,
      interface_density: Default,
    )
  '';
}

Wallpaper Configuration:

{
  # Set wallpaper via COSMIC settings
  xdg.configFile."cosmic/com.system76.CosmicSettings.Wallpaper/v1/".text = ''
    (
      wallpapers: [
        (
          path: "/path/to/wallpaper.png",
          method: Zoom,
        ),
      ],
    )
  '';
}

Font Configuration

{
  # System-wide fonts (affects COSMIC)
  fonts = {
    enableDefaultPackages = true;
    packages = with pkgs; [
      noto-fonts
      noto-fonts-cjk
      noto-fonts-emoji
      (nerdfonts.override { fonts = [ "JetBrainsMono" "FiraCode" ]; })
    ];

    fontconfig = {
      defaultFonts = {
        serif = [ "Noto Serif" ];
        sansSerif = [ "Noto Sans" ];
        monospace = [ "JetBrainsMono Nerd Font" ];
        emoji = [ "Noto Color Emoji" ];
      };
    };
  };
}

Keyboard Shortcuts

Default Shortcuts

Window Management:

  • Super + Tab / Alt + Tab - Switch windows
  • Super + Q - Close window
  • Super + M - Maximize/restore window
  • Super + R - Resize mode (use arrows to resize)
  • Super + Shift + R - Resize opposite direction
  • Super + G - Toggle tiling/floating mode

Workspace Management:

  • Super + 1-9 - Switch to workspace
  • Super + Shift + 1-9 - Move window to workspace
  • Super + Ctrl + Left/Right - Switch workspace
  • Super + Shift + Ctrl + Left/Right - Move window to adjacent workspace

Launcher and Tools:

  • Super + / - Open launcher
  • Super + T - Open terminal
  • Super + E - Open file manager
  • Super + L - Lock screen
  • Super + Esc - Power menu

Tiling Shortcuts:

  • Super + Left/Right/Up/Down - Tile window in direction
  • Super + Enter - Swap with master

Custom Keyboard Shortcuts

Via Home Manager (RON configuration):

{
  xdg.configFile."cosmic/com.system76.CosmicComp/v1/keybindings".text = ''
    (
      bindings: {
        // Custom terminal launcher
        (Modifiers(Super), "Return"): System(Terminal),

        // Custom browser launcher
        (Modifiers(Super), "b"): Spawn("firefox"),

        // Screenshot
        (Modifiers(Super Shift), "s"): System(Screenshot),

        // Custom workspace switching
        (Modifiers(Super), "bracketleft"): Workspace(Previous),
        (Modifiers(Super), "bracketright"): Workspace(Next),
      },
    )
  '';
}

Troubleshooting

1. NVIDIA Phantom Display Issue

Problem: Extra phantom display appears with NVIDIA GPUs

Solution:

{
  boot.kernelParams = [ "nvidia_drm.fbdev=1" ];
}

2. Clipboard Not Working

Problem: Copy/paste between applications fails

Solution:

{
  environment.sessionVariables.COSMIC_DATA_CONTROL_ENABLED = "1";
}

3. Observatory Service Not Starting

Problem: System monitoring tool (Observatory) doesn't start

Solution:

{
  systemd.packages = [ pkgs.observatory ];
  systemd.services.monitord.wantedBy = [ "multi-user.target" ];
}

4. Settings Not Persisting

Problem: Changes in COSMIC Settings don't persist after reboot

Causes:

  • Home Manager overwriting config files
  • Conflicting declarative and imperative configurations
  • Incorrect file permissions

Solution:

{
  # Option 1: Remove Home Manager config file management
  # Comment out xdg.configFile for COSMIC settings

  # Option 2: Use Home Manager force option
  xdg.configFile."cosmic/...".force = true;

  # Option 3: Exclude specific paths from Home Manager
  home.file = {
    ".config/cosmic".source = lib.mkForce null;
  };
}

5. Applets Not Loading

Problem: Panel applets don't appear or crash

Debugging:

# Check applet logs
journalctl --user -u cosmic-panel -f

# Verify applet configuration
cat ~/.config/cosmic/com.system76.CosmicPanel.Panel/v1/plugins_wings

# Reset applet configuration
rm -rf ~/.config/cosmic/com.system76.CosmicPanel.Panel/

Solution: Ensure RON syntax is valid and applet names are correct

6. Theme Not Applying

Problem: Custom theme doesn't take effect

Solution:

# Restart COSMIC session
cosmic-session --reload

# Or log out and log back in

# Verify theme file syntax
cat ~/.config/cosmic/com.system76.CosmicTheme.Dark/v1/

7. Slow Performance

Problem: Laggy desktop, slow animations

Solutions:

{
  # Enable System76 scheduler
  services.system76-scheduler.enable = true;

  # Reduce compositor effects
  xdg.configFile."cosmic/com.system76.CosmicComp/v1/animations".text = ''
    (
      enabled: false,
    )
  '';

  # Disable transparency
  xdg.configFile."cosmic/com.system76.CosmicComp/v1/opacity".text = ''
    (
      window: 1.0,
      panel: 1.0,
    )
  '';
}

8. Flatpak Apps Not Theming Correctly

Problem: Flatpak applications don't match COSMIC theme

Solution:

# Install COSMIC theme for Flatpak
flatpak install org.gtk.Gtk3theme.cosmic
flatpak install org.kde.KStyle.cosmic

# Force Flatpak to use system theme
flatpak override --user --env=GTK_THEME=cosmic

9. Multi-Monitor Issues

Problem: Incorrect display layout or resolution

Solution:

{
  # Use COSMIC Settings UI for initial setup
  # Then capture configuration:
  xdg.configFile."cosmic/com.system76.CosmicComp/v1/outputs".text = ''
    (
      outputs: {
        "DP-1": (
          mode: (1920, 1080, 60.0),
          position: (0, 0),
          scale: 1.0,
          transform: Normal,
        ),
        "HDMI-1": (
          mode: (1920, 1080, 60.0),
          position: (1920, 0),
          scale: 1.0,
          transform: Normal,
        ),
      },
    )
  '';
}

10. Flake Build Failures

Problem: Building from nixos-cosmic flake fails

Solutions:

# Ensure substituters are set FIRST
nixos-rebuild test  # Sets up binary cache

# Then rebuild with COSMIC
nixos-rebuild switch --flake .#hostname

# For low-memory systems
nixos-rebuild switch --flake .#hostname --cores 1 -j 1

# Update flake inputs
nix flake update

Discovery and Debugging Tools

Configuration Discovery

Find Configuration Files:

# List all COSMIC config directories
ls -la ~/.config/cosmic/

# View component configuration
cat ~/.config/cosmic/com.system76.CosmicPanel.Panel/v1/plugins_wings

# Watch configuration changes in real-time
watch -n 1 'ls -lt ~/.config/cosmic/*/v1/*'

Monitor COSMIC Processes:

# View running COSMIC components
ps aux | grep cosmic

# Monitor resource usage
htop -p $(pgrep -d',' cosmic)

Log Analysis

Component Logs:

# Panel logs
journalctl --user -u cosmic-panel -f

# Compositor logs
journalctl --user -u cosmic-comp -f

# Greeter logs
journalctl -u cosmic-greeter -f

# All COSMIC logs
journalctl --user -t cosmic -f

Session Debugging:

# Start COSMIC session with debug output
RUST_LOG=debug cosmic-session

# Or set in configuration:
environment.sessionVariables.RUST_LOG = "debug";

Testing Configuration Changes

Safe Testing Workflow:

# 1. Backup current config
cp -r ~/.config/cosmic ~/.config/cosmic.backup

# 2. Make changes via Home Manager or direct edit

# 3. Test without rebuilding (if manual edit)
cosmic-session --reload

# 4. If using Home Manager, test first
home-manager switch --flake .#user

# 5. Verify changes took effect
diff ~/.config/cosmic ~/.config/cosmic.backup

Binary Cache Verification

Check Substituter Status:

# Verify binary cache is configured
nix show-config | grep substituters

# Test cache availability
nix store ping --store https://cosmic.cachix.org/

# Check cache statistics
nix path-info --all --store https://cosmic.cachix.org/ | wc -l

Golden Path: Best Practices

1. ✅ Use Native NixOS Module (25.05+)

Do: Start with the native NixOS module for stability

services.desktopManager.cosmic.enable = true;
services.displayManager.cosmic-greeter.enable = true;

Why: Official support, binary cache, less maintenance

2. ✅ Enable Binary Cache First

Do: Configure substituters BEFORE adding COSMIC packages

nix.settings = {
  substituters = [ "https://cosmic.cachix.org/" ];
  trusted-public-keys = [ "cosmic.cachix.org-1:Dya9IyXD4xdBehWjrkPv6rtxpmMdRel02smYzA85dPE=" ];
};

Why: Avoids lengthy local builds (~40GB, 16GB RAM requirement)

3. ✅ Use Home Manager for User Config

Do: Manage user-specific COSMIC settings via Home Manager

xdg.configFile."cosmic/com.system76.CosmicPanel.Panel/v1/plugins_wings".text = ''...'';

Why: Declarative, version-controlled, reproducible across machines

4. ✅ Enable System76 Scheduler

Do: Enable the scheduler for better performance

services.system76-scheduler.enable = true;

Why: Optimizes process scheduling for desktop responsiveness

5. ✅ Test Configuration Incrementally

Do: Build and test before committing

# Test first
nixos-rebuild test

# If successful, switch
nixos-rebuild switch

Why: Allows rollback without reboot if something breaks

6. ✅ Validate RON Syntax

Do: Validate RON files before deploying

# Check for syntax errors
cat ~/.config/cosmic/file.ron | cosmic-settings --validate-ron

Why: Invalid RON causes silent failures or crashes

7. ✅ Version Your Configuration

Do: Use versioned directories in COSMIC config paths

xdg.configFile."cosmic/com.system76.CosmicComp/v1/...".text = ''...'';

Why: Future COSMIC versions may use v2, v3, etc.

8. ✅ Exclude Unwanted Packages

Do: Minimize installation footprint

environment.cosmic.excludePackages = with pkgs; [
  cosmic-edit
  cosmic-term
];

Why: Reduces disk usage and potential conflicts

9. ✅ Document Custom Settings

Do: Add comments to your configuration

# Custom keyboard layout: US with Caps as Escape
xdg.configFile."cosmic/com.system76.CosmicComp/v1/xkb_config".text = ''
  (
    layout: "us",
    options: Some("caps:escape"),
  )
'';

Why: Future you (or team members) will understand the choices

10. ✅ Monitor Development Progress

Do: Track COSMIC development and NixOS integration

Why: Stay informed about breaking changes and new features

Anti-Patterns: What to Avoid

1. ❌ Mixing Imperative and Declarative Config

Don't: Use COSMIC Settings GUI AND Home Manager for same settings

# Bad: This will be overwritten by Home Manager
# Then manually changing in COSMIC Settings
xdg.configFile."cosmic/...".text = ''...'';

Why: Creates conflicts, settings don't persist

Do Instead: Choose one approach - preferably Home Manager for reproducibility

2. ❌ Skipping Binary Cache Setup

Don't: Add COSMIC without configuring substituters

# Bad: Will trigger massive local build
services.desktopManager.cosmic.enable = true;
# (without substituters configured)

Why: Requires 16GB RAM, 40GB disk, hours of compilation

Do Instead: Configure binary cache FIRST, then enable COSMIC

3. ❌ Hardcoding Paths

Don't: Use absolute paths in configuration

# Bad: Not portable
xdg.configFile."cosmic/wallpaper".source = /home/user/pictures/wall.png;

Why: Breaks on other machines, not reproducible

Do Instead: Use relative paths or package references

xdg.configFile."cosmic/wallpaper".source = ./wallpapers/default.png;

4. ❌ Ignoring RON Syntax Errors

Don't: Deploy invalid RON configuration

# Bad: Invalid RON syntax
(
  entries: [
    CosmicAppletTime,  # Missing comma or wrong format
    CosmicAppletAudio
  ]
)

Why: Silent failures, applets won't load

Do Instead: Validate RON syntax, test incrementally

5. ❌ Using Bleeding Edge Without Understanding

Don't: Use nixos-cosmic flake without understanding implications

# Bad: Blindly using development version
inputs.nixpkgs.follows = "nixos-cosmic/nixpkgs";

Why: Unstable, frequent breaking changes, no guarantees

Do Instead: Use native NixOS module unless you need cutting-edge features

6. ❌ Not Restarting COSMIC Session

Don't: Expect configuration changes to apply without restart

# Bad: Edit config and expect immediate effect
nano ~/.config/cosmic/...
# No restart

Why: Most settings require session restart

Do Instead: Restart session after changes

cosmic-session --reload
# Or log out and back in

7. ❌ Overusing environment.systemPackages

Don't: Install user applications system-wide

# Bad: Installing user apps system-wide
environment.systemPackages = with pkgs; [
  cosmic-edit
  cosmic-term
  firefox
  vscode
];

Why: Clutters system, applies to all users

Do Instead: Use Home Manager for user applications

home.packages = with pkgs; [ cosmic-edit cosmic-term ];

8. ❌ Ignoring COSMIC Version Compatibility

Don't: Mix COSMIC versions or ignore version warnings

# Bad: Using incompatible package versions
environment.systemPackages = [ pkgs.cosmic-edit ];
services.desktopManager.cosmic.enable = true;
# (from different nixpkgs commits)

Why: API incompatibilities, crashes

Do Instead: Ensure consistent COSMIC package versions

9. ❌ Disabling Security Features Without Reason

Don't: Globally disable Wayland security

# Bad: Unnecessary security compromise
environment.sessionVariables = {
  COSMIC_DATA_CONTROL_ENABLED = "1";
  MOZ_ENABLE_WAYLAND = "0";  # Disabling Wayland entirely
};

Why: Reduces security for no benefit

Do Instead: Enable only what's needed, understand implications

10. ❌ Not Backing Up Configuration

Don't: Make major changes without backup

# Bad: Deleting config without backup
rm -rf ~/.config/cosmic/

Why: May lose working configuration, hard to recover

Do Instead: Always backup before major changes

cp -r ~/.config/cosmic ~/.config/cosmic.backup.$(date +%Y%m%d)

Complete Configuration Examples

Example 1: Developer Workstation

Full NixOS + Home Manager Setup:

# configuration.nix
{ config, pkgs, ... }:
{
  # COSMIC Desktop
  services.desktopManager.cosmic.enable = true;
  services.displayManager.cosmic-greeter.enable = true;

  # Performance
  services.system76-scheduler.enable = true;

  # Flatpak for COSMIC Store
  services.flatpak.enable = true;

  # Clipboard support
  environment.sessionVariables.COSMIC_DATA_CONTROL_ENABLED = "1";

  # Development tools
  environment.systemPackages = with pkgs; [
    git
    vim
  ];

  # Minimal COSMIC apps
  environment.cosmic.excludePackages = with pkgs; [
    cosmic-edit  # Using VSCode instead
  ];
}

# home.nix
{ config, pkgs, ... }:
{
  home.packages = with pkgs; [
    cosmic-term
    cosmic-files
    firefox
    vscode
  ];

  # Panel configuration
  xdg.configFile = {
    "cosmic/com.system76.CosmicPanel.Panel/v1/plugins_wings".text = ''
      (
        entries: [
          CosmicAppletWorkspaces,
          CosmicAppletApplications,
          CosmicAppletAudio,
          CosmicAppletNetwork,
          CosmicAppletBattery,
          CosmicAppletTime,
          CosmicAppletNotifications,
        ],
      )
    '';

    # Dark theme
    "cosmic/com.system76.CosmicTheme.Dark/v1/".text = ''
      (
        base: (
          palette: Dark,
          neutral_tint: Some(Rgb(0.15, 0.2, 0.25)),
          accent: Rgb(0.4, 0.6, 1.0),
        ),
      )
    '';

    # Tiling enabled by default
    "cosmic/com.system76.CosmicComp/v1/autotile".text = ''
      (
        enabled: true,
        behavior: Global,
        gap: 8,
      )
    '';

    # Keyboard shortcuts
    "cosmic/com.system76.CosmicComp/v1/xkb_config".text = ''
      (
        rules: "",
        model: "",
        layout: "us",
        variant: "",
        options: Some("caps:escape"),
      )
    '';
  };
}

Example 2: Minimal COSMIC (Flake-Based)

For Cutting-Edge Testing:

# flake.nix
{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    nixos-cosmic.url = "github:lilyinstarlight/nixos-cosmic";
  };

  outputs = { nixpkgs, nixos-cosmic, ... }: {
    nixosConfigurations.cosmic-test = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
        {
          nix.settings = {
            substituters = [ "https://cosmic.cachix.org/" ];
            trusted-public-keys = [
              "cosmic.cachix.org-1:Dya9IyXD4xdBehWjrkPv6rtxpmMdRel02smYzA85dPE="
            ];
            experimental-features = [ "nix-command" "flakes" ];
          };
        }

        nixos-cosmic.nixosModules.default

        {
          services.desktopManager.cosmic.enable = true;
          services.displayManager.cosmic-greeter.enable = true;
          services.system76-scheduler.enable = true;

          users.users.user = {
            isNormalUser = true;
            extraGroups = [ "wheel" "networkmanager" ];
          };
        }
      ];
    };
  };
}

Example 3: Multi-Monitor Setup

# home.nix
{
  xdg.configFile = {
    # Display configuration
    "cosmic/com.system76.CosmicComp/v1/outputs".text = ''
      (
        outputs: {
          "DP-1": (
            mode: (2560, 1440, 144.0),
            position: (0, 0),
            scale: 1.0,
            transform: Normal,
          ),
          "HDMI-1": (
            mode: (1920, 1080, 60.0),
            position: (2560, 0),
            scale: 1.0,
            transform: Normal,
          ),
        },
      )
    '';

    # Workspace per monitor
    "cosmic/com.system76.CosmicComp/v1/workspaces".text = ''
      (
        workspace_mode: OutputBound,
        workspace_layout: Horizontal,
      )
    '';
  };
}

Resources and References

Official Documentation

Community

Related Issues

Learning Resources

Remember: COSMIC is actively developed. Configuration patterns may change. Always check the official NixOS wiki and nixos-cosmic repository for the latest information.

Install

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82/100Analyzed 2/6/2026

A high-quality technical guide for the COSMIC Desktop Environment on NixOS, providing detailed installation methods and declarative configuration examples. It is slightly truncated at the end.

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