name: configuring-layers description: "khanelinix 7-level configuration hierarchy and customization strategy. Use when deciding where to put customizations, understanding override precedence, resolving option conflicts, or working with host/user specific configs."

Configuration Layering

7-Level Hierarchy

From lowest to highest precedence:

1. Common modules - Cross-platform base functionality
2. Platform modules - OS-specific (nixos/darwin)
3. Home modules - User-space applications
4. Suite modules - Grouped functionality with defaults
5. Archetype modules - High-level use case profiles
6. Host configs - Host-specific overrides
7. User configs - User-specific customizations (highest priority)

Quick Decision Tree

Question: Where should I put this configuration?

1. Does it require sudo/root access? → System modules (nixos/ or darwin/)
2. Is it hardware-specific? → Host config (systems/{arch}/{hostname}/)
3. Is it user-preference specific? → User config (homes/{arch}/{user@host}/)
4. Does it configure user applications? → Home modules (modules/home/)
5. Is it shared across platforms? → Common modules (modules/common/)

Still unsure? Default to home modules - they're easiest to test and most portable.

Customization Strategy

Host Configuration

systems/{arch}/{hostname}/
├── default.nix       # Host-specific system config
└── hardware.nix      # Hardware-specific settings

Example: systems/x86_64-linux/khanelimain/default.nix

User Configuration

homes/{arch}/{username@hostname}/
├── default.nix       # User-specific home config
└── packages.nix      # User-specific packages

Example: homes/x86_64-linux/khaneliman@khanelimain/default.nix

Override Precedence

# In module (low priority - can be overridden)
programs.git.userName = lib.mkDefault "Default Name";

# In host config (overrides module default)
programs.git.userName = "Host Specific";

# Force (highest priority - rarely needed)
programs.git.userName = lib.mkForce "Forced Value";

Override Patterns by Use Case

Pattern 1: Testing a new value (keep module default)

# In home config - temporarily override
programs.git.userName = "Test Name";  # Plain assignment

# Module default still exists for other hosts

Pattern 2: Setting project-wide standard (weak default)

# In module
programs.git.userName = lib.mkDefault "Default Name";

# Easily overridden in host/user configs

Pattern 3: Enforcing a requirement (strong override)

# In security-critical module
security.sudo.wheelNeedsPassword = lib.mkForce true;

# Cannot be overridden by downstream configs

Common Override Scenarios

Scenario: Different git config per host

# modules/home/programs/terminal/tools/git/default.nix
programs.git.userName = lib.mkDefault "khaneliman";

# homes/x86_64-linux/khaneliman@workhost/default.nix
programs.git.userName = "Work Name";  # Overrides for this host

# homes/x86_64-linux/khaneliman@personalhost/default.nix
# Uses module default ("khaneliman")

Scenario: Override theme but not fonts

# Suite sets defaults
khanelinix.user.theme = lib.mkDefault "catppuccin-mocha";
khanelinix.user.font.mono = lib.mkDefault "JetBrainsMono";

# User overrides just theme
khanelinix.user.theme = "gruvbox";  # Plain assignment overrides mkDefault
# Font remains JetBrainsMono from suite

Best Practice

Prefer customization in this order:

1. Home configuration wherever possible
2. Host config for hardware/host-specific
3. Platform modules for OS-specific behavior
4. Common modules for shared base functionality

See Also

• Module placement: See scaffolding-modules for determining where to place configuration
• Option design: See designing-options for creating properly namespaced options