Both examples create a service from a c# mono application.

Snap Service

The below yaml file copies all files from the local ./build/Release folder into the root of the snap. It installes all packages fro state-packages as dependencies that the service will require.

your-program-service-name.yaml

name: your-program-service-name
version: 0.1
summary: Your programs summary
description: 
  A description of what this service does
confinement: strict

apps:
  your-program-service-name-searcher:
    command: mono $SNAP/YourProgramName.exe
    plugs: [network-bind]
    daemon: simple

parts:
  your-program-service-name-searcher-bin:
    plugin: copy
    files:
       "./build/Release/*": "."
    stage-packages:
      - mono-runtime
      - libmono-corlib4.5-cil
      - libmono-system-core4.0-cil
      - libmono-system-net-http4.0-cil
      - libmono-system-runtime4.0-cil
      - libmono-system-web-extensions4.0-cil
      - libmono-system-xml4.0-cil
      - libmono-system-web4.0-cil
      - libmono-system-web-http4.0-cil
      - libmono-system-xml-linq4.0-cil
      - libmono-microsoft-csharp4.0-cil
      - libmono-http4.0-cil
      - curl

To build the snap package run

snapcraft clean
mkdir -p build
snapcraft snap -o "$(pwd)/build/your-program-service-name.snap"

To install the snap without uploading to the ubuntu snap store run

snap install "${pwd}/build/your-program-service-name.snap" --force-dangerous'

At this point your c# console app should be running as a systemd service.

Systemd service

Another way to create a service is to use systemd directly.

[Unit]
Description=The description of your service
# How to install:
# Copy YourProgramName binary to /opt/your-program-service-name/YourProgramName.exe
# Copy /etc/systemd/system/your-program-service-name.service
# systemctl enable your-program-service-name.service
# systemctl start your-program-service-name.service

[Service]
ExecStart=mono /opt/your-program-service-name/YourProgramName.exe
Restart=always
RestartSec=10                       # Restart service after 10 seconds if node service crashes
StandardOutput=syslog               # Output to syslog" >> /etc/systemd/system/your-program-service-name.service
StandardError=syslog                # Output to syslog" >> /etc/systemd/system/your-program-service-name.service
SyslogIdentifier=your-program-service-name
WorkingDirectory=/opt/your-program-service-name/YourProgramName.exe

[Install]
WantedBy=multi-user.target