Fixed Buffer

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Threading.Tasks;

namespace PostServicioNetCore
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var host = new HostBuilder()
                 .ConfigureHostConfiguration(configHost =>
                 {
                     //Configuración del host
                 })
                 .ConfigureAppConfiguration((hostContext, configApp) =>
                 {
                     //Configuración de la aplicacion

                 })
                .ConfigureServices((hostContext, services) =>
                {
                    //Configuración de los servicios
                    services.AddHostedService<LifetimeHostedService>();
                });
            if (!Debugger.IsAttached) //En caso de no haber debugger, lanzamos como servicio
            {
                await host.RunServiceAsync();
            }
            else
            {
                await host.RunConsoleAsync();
            }
        }
    }
}

using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

namespace PostServicioNetCore
{
    public class LifetimeHostedService : IHostedService, IDisposable
    {
        ILogger<LifetimeHostedService> logger;
        private Timer _timer;
        private string _path;
        public LifetimeHostedService(ILogger<LifetimeHostedService> logger, IHostingEnvironment hostingEnvironment)
        {
            this.logger = logger;
            _path = $"{hostingEnvironment.ContentRootPath}PostServicioCore.txt";
        }

        public Task StartAsync(CancellationToken cancellationToken)
        {
            try
            {
                WriteToFile("Inicia el servicio");
                _timer = new Timer((e) => WriteTimeToFile(), null, TimeSpan.Zero, TimeSpan.FromMinutes(1));
            }
            catch (Exception ex)
            {
                logger.LogError($"{ex.Message},{ex.StackTrace}");
            }
            return Task.CompletedTask;
        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            _timer?.Change(Timeout.Infinite, 0);
            WriteToFile("Finaliza el servicio");
            return Task.CompletedTask;
        }

        private void WriteTimeToFile()
        {
            WriteToFile(DateTime.Now.ToString());
        }

        private void WriteToFile(string message)
        {
            if (!File.Exists(_path))
            {
                using (var sw = File.CreateText(_path))
                {
                    sw.WriteLine(message);
                }
            }
            else
            {
                using (var sw = File.AppendText(_path))
                {
                    sw.WriteLine(message);
                }
            }
        }

        public void Dispose()
        {
            _timer?.Dispose();
        }
    }
}

using Microsoft.Extensions.Hosting;
using System;
using System.ServiceProcess;
using System.Threading;
using System.Threading.Tasks;

namespace PostServicioNetCore
{
    public class ServiceBaseLifetime : ServiceBase, IHostLifetime
    {
        private readonly TaskCompletionSource<object> _delayStart = new TaskCompletionSource<object>();

        public ServiceBaseLifetime(IApplicationLifetime applicationLifetime)
        {
            ApplicationLifetime = applicationLifetime ?? throw new ArgumentNullException(nameof(applicationLifetime));
        }

        private IApplicationLifetime ApplicationLifetime { get; }

        public Task WaitForStartAsync(CancellationToken cancellationToken)
        {
            cancellationToken.Register(() => _delayStart.TrySetCanceled());
            ApplicationLifetime.ApplicationStopping.Register(Stop);

            new Thread(Run).Start(); //Ejecutamos la tarea en un hilo para bloquear y prevenir que IHost.StartAsync termine.
            return _delayStart.Task;
        }

        private void Run()
        {
            try
            {
                Run(this); // Bloqueamos la ejecución hasta que el servicio termine.
                _delayStart.TrySetException(new InvalidOperationException("Stopped without starting"));
            }
            catch (Exception ex)
            {
                _delayStart.TrySetException(ex);
            }
        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            Stop();
            return Task.CompletedTask;
        }

        // Se llama desde base.Run() cuando el servicio esta listo para funcionar.
        protected override void OnStart(string[] args)
        {
            _delayStart.TrySetResult(null);
            base.OnStart(args);
        }

        protected override void OnStop()
        {
            ApplicationLifetime.StopApplication();
            base.OnStop();
        }
    }
}

using System.Runtime.InteropServices;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System.Threading;
using System.Threading.Tasks;

namespace PostServicioNetCore
{
    public static class ServiceBaseLifetimeHostExtensions
    {
        public static IHostBuilder UseServiceBaseLifetime(this IHostBuilder hostBuilder)
        {
            return hostBuilder.ConfigureServices((hostContext, services) => services.AddSingleton<IHostLifetime, ServiceBaseLifetime>());
        }

        public static Task RunServiceAsync(this IHostBuilder hostBuilder, CancellationToken cancellationToken = default)
        {
            //Si es Windows, añadimos el ServiceBaseLifetime a la inyeccion de dependencias
            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            {
                return hostBuilder.UseServiceBaseLifetime().Build().RunAsync(cancellationToken);
            }
            else //Sino, ejecutamos normalmente
            {
                return hostBuilder.Build().RunAsync(cancellationToken);
            }
        }
    }
}

sc create "Servicio Core" binpath= "C:\Users\jorge\source\repos\PostServicioNetCore\PostServicioNetCore\bin\Release\netcoreapp2.2\publish\PostServicioNetCore.exe"