Writing your first .Net Core 2.0 systemd service

This tutorial will cover the basics of writing a systemd daemon using .Net Core 2.0 on Linux. For background on writing “new style” (systemd compatible) daemons, see the documentation. This tutorial assumes you already have a working .Net Core installation. If not, follow the instructions here to install .Net.

Getting started

Run dotnet new console -o myfirstdaemon. This will generate a myfirstdaemon directory containing the following files:

service.csproj
Program.cs

Open the Program.cs file with the text editor of your choice. We will now begin working on the logic of our daemon.

1. First we need to set up signal handlers for SIGINT (Ctrl-C) and SIGTERM (sent by systemd upon daemon termination). Add the following lines in Main:

   AssemblyLoadContext.Default.Unloading += SigTermEventHandler; //register sigterm event handler. Don't forget to import System.Runtime.Loader!
   Console.CancelKeyPress += CancelHandler; //register sigint event handler
   

2. Then add the event handler methods in the Program class:

   private static void SigTermEventHandler(AssemblyLoadContext obj)
   {
   	System.Console.WriteLine("Unloading...");
   }
   
   private static void CancelHandler(object sender, ConsoleCancelEventArgs e)
   {	     
   	System.Console.WriteLine("Exiting...");
   }
   

3. Finally, add the main daemon logic in Main:

   while(true)
   {
   	Console.WriteLine("Hello World!");
   	Thread.Sleep(2000); //Sleep for 2 seconds. Don't forget to import System.Threading!
   }
   

4. Publish your app: dotnet publish -o /opt/daemons/myfirstdaemon/

5. Now we need to tell systemd about our service. We’re going to use systemd user units. Run systemctl edit --user --full --force myfirstdaemon.service and add the following contents:

   [Unit]
   Description=Test .Net service
   
   [Service]
   ExecStart=/usr/local/bin/dotnet /opt/daemons/myfirstdaemon/myfirstdaemon.dll #Tell systemd which program to start
   

6. Run your service: systemctl start --user myfirstdaemon.service. You should be able to see the output by running systemctl status --user myfirstdaemon.service or journalctl --user -u myfirstdaemon.service

That’s it! You now know how to write a very simple .Net Core daemon managed by systemd. To view the full source code, please visit my Github.