Failed to start jenkins.service: Unit not found.

As an AI language model, I do not have access to your system, so I can only provide general troubleshooting steps.

Here are some possible reasons and solutions for the error message "Failed to start jenkins.service: Unit not found":

1. Jenkins is not installed: Make sure Jenkins is installed on your system. You can install it using the official installation guide for your operating system.

2. Jenkins service is not enabled: If Jenkins is installed but the service is not enabled, you can enable it using the command:

   sudo systemctl enable jenkins.service

3. Jenkins service is not running: If Jenkins is installed and the service is enabled, but it still fails to start, try starting the service manually using the command:

   sudo systemctl start jenkins.service

4. Jenkins service file is missing or corrupted: If none of the above solutions work, there might be an issue with the Jenkins service file. You can try reinstalling the Jenkins package or downloading the service file from the official Jenkins GitHub repository.

5. Jenkins is not supported on your operating system: Check the official documentation to see if Jenkins is supported on your operating system. If it is not, you might need to use a different solution or install Jenkins in a virtual machine.

I hope these solutions help you resolve the issue with starting the Jenkins service.