If you are working in an enterprise setting, utilising Azure to host and run services as a Azure Functions and WebJobs makes life easier.
But what about hosting on Linux?
With .NET Core, you can! That's why, in this article, I will describe how to create a passive Console Application which runs as a cron job on a Linux server such as a Ubuntu.
You will need...
- dotnet SDK installed
- Command prompt (cmd.exe)
- Notepad (or another basic text editor)
- Ubuntu server via SSH or the terminal
- sftp and cron installed on your Ubuntu server
Building a passive console application
The easiest way to create a simple console application does not even require you to open Visual Studio.
Instead, open Command Prompt (Windows Key + R, type cmd, hit Enter).
Use the cd command to change directory and navigate to where you want to create your test application. I'm using C:\Users\AntonyAllen\source\repos>
Once in your directory, use the mkdir command to make a new folder for you:
Now to create the console application in this folder.
dotnet new console
Now, let's edit our application.
Change the contents of the static void Main function to:
Console.WriteLine("This is a test!");
Now save and close Notepad.
Verify that your changes were saved by typing the following in Command Prompt:
What is a passive application?
By passive, I mean to say that there should be no interaction with the user in the console application. So, no Console.ReadKey() or .ReadLine(), or any other function which requires user input. When running as a background process in Linux, this will cause an infinite loop to occur.
Build and Publish
Now we need to publish our application.
For the sake of simplicity, we can publish a self-contained application that we can deploy to our Ubuntu server. However, it is of course possible to install the dotnet runtime directly on Ubuntu, so we do not need to publish the Core DLL files.
dotnet publish -c release -r ubuntu.18.04-x64
This will publish for the 64-bit edition of Ubuntu 18.04, so you may need to change the runtime accordingly.
Now, navigate through the directory structure to see what was published:
As you can see, there are a lot of .dll files in that folder, and some *.so files, amongst others.
Your executable is called MyLinuxApp (without an extension).
Transfer files to your Ubuntu server
For this next stage, I won't go into detail, but essentially, you need to transfer the contents of the "publish" folder we just created to your Ubuntu server.
Use sftp from Command Prompt as follows:
Once you're in, you can use the recursive put command to place the files into your desired folder on the server:
put -r "C:\Users\AntonyAllen\source\repos\MyLinuxApp\bin\release\net5.0\ubuntu.18.04-x64\publish" "MyLinuxApp"
Obviously, you need to provide the correct directory from your local machine.
Once the files are uploaded, get out of sftp by typing:
Run the app inside Ubuntu
Use SSH to get into your server from Command Prompt
Locate the folder that you just uploaded.
If you've done everything correctly, you should see the published files on your Ubuntu server.
Set the executable permission
In order to run our app, we need to add the right permission:
chmod +x MyLinuxApp
Run the app in SSH
Let's try running our app:
If all is well, you will see "This is a test!"
Setup the Cron Job
Now to configure our passive console application to run as a "service" in Linux Ubuntu.
More specifically, we will use the cron system to schedule the app every 1 minute.
To access the cron task definition list, type:
Now, you can use GNU nano or another text editor to add the following line to the end of the file:
* * * * * cd ~/MyLinuxApp && ./MyLinuxApp > ~/test.log
Now hit Ctrl+X, Y, and Enter to save and close the file.
Wait a minute for the cron job to run, and then type:
If the file exists, and you read the contents "This is a test!" then congratulations, you have just created your first Ubuntu cron job running a .NET console application!
- Create a passive Console Application in .NET Core (3.1, 5.0, 6.0, etc.)
- Publish the app with dotnet publish for the target environment
- Transfer files to your Linux server
- Set the correct permissions using chmod
- Add the task to the crontab
Thanks for reading! Please share this article and come back soon! 😊