Local Configuration

You can customize the system’s configuration for managed components with config files that are located in /etc/local/*.

Every component that supports customizing its configuration creates a directory writable by service users, such as /etc/local/firewall. The specific format and allowed filenames depend on the specifics of each component and are documented separately.

Changes to the files in the local configuration directory are picked up automatically upon the next run of our configuration agent (generally every 10 minutes) but you can also explicitly trigger it by running:

$ sudo fc-manage --build

This will update the machine’s system configuration, which includes copying the local configuration files into the Nix store. Your custom config is thus versioned along the general system config (in case we have to revert to an older configuration version) and is atomically loaded and activated.

To inspect the result of this call, you can check the journal:

$ journalctl --since -1h --unit fc-manage

Custom NixOS Configuration

You can put custom NixOS modules in /etc/local/nixos that are included in the system’s configuration. See custom.nix.example for the basic structure of a NixOS module. All options offered by NixOS and our platform code can be set there.


Care must be taken to avoid breaking the system. Overriding options set by platform can be dangerous. Use component-specific local config dirs if possible.

For more information about writing NixOS modules, refer to the NixOS manual

NixOS options can be looked up here (may not be accurate due to version differences):