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Your First Systemd Service

This tutorial walks you through creating and managing a systemd service with System Manager.

Prerequisites

  • System Manager initialized (see Getting Started)
  • Basic familiarity with Nix syntax

What You'll Build

A simple "hello world" systemd service that runs when System Manager activates your configuration.

Step 1: Create a Service Module

Create a file called hello-service.nix in your ~/.config/system-manager/ folder:

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{ lib, pkgs, ... }:
{
  config = {
    nixpkgs.hostPlatform = "x86_64-linux";

    systemd.services.say-hello = {
      description = "say-hello";
      enable = true;
      wantedBy = [ "system-manager.target" ];
      serviceConfig = {
        Type = "oneshot";
        RemainAfterExit = true;
      };
      script = ''
        ${lib.getBin pkgs.hello}/bin/hello
      '';
    };
  };
}

Let's break down what each part does:

  • systemd.services.say-hello: Creates a service named "say-hello".
  • enable = true: Activates the service.
  • wantedBy = [ "system-manager.target" ]: Starts the service when System Manager activates.
  • Type = "oneshot": Runs once and exits.
  • RemainAfterExit = true: Keeps the service marked as "active" after the script finishes.
  • script: The actual command to run.

Step 2: Add the Module to Your Flake

Edit your flake.nix and add the new module:

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modules = [
    ./system.nix
    ./hello-service.nix
];

Step 3: Apply the Configuration

Run System Manager to activate your new service:

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nix run 'github:numtide/system-manager' -- switch --flake . --sudo

Step 4: Verify It Worked

Check the journal to see if your service ran:

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journalctl -n 20

You should see output like:

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Nov 18 12:12:51 my-ubuntu systemd[1]: Starting say-hello.service - say-hello...
Nov 18 12:12:51 my-ubuntu say-hello-start[3488278]: Hello, world!
Nov 18 12:12:51 my-ubuntu systemd[1]: Finished say-hello.service - say-hello.

Step 5: Check the Generated Service File

System Manager created a systemd unit file at /etc/systemd/system/say-hello.service. You can view it with:

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cat /etc/systemd/system/say-hello.service

Next Steps