UWP applications have restricted access to the local file system and this can cause a few issues when using logging frameworks if you’re expecting to write logs to c:\Temp
or %Temp% locations (for example).

Your UWP application can write to the application’s installation folder, for example

var installedLocation = 
   Windows.ApplicationModel.Package.Current.InstalledLocation.Path;

another alternatively is application data location, such as

var localFolder = 
   ApplicationData.Current.LocalFolder.Path;

// or

var localCache = 
   ApplicationData.Current.LocalCacheFolder.Path;

These last two location will translate to a location such as the following, where username is the (as you’d expect) username the user logged into the machine with, and the GUID is the package family name GUID (taken from the application’s manifest). This is actually an extended GUID.

C:\Users\<username>\AppData\Local\Packages\<guid>

Note: At the time of writing I’m not sure where the string after the underscore which follows the GUID comes from.

Let’s take a quick look at using Serilog’s File Sink to write our log files. Using NuGet install Serilog and Serilog.Sink.File and use the following code

Log.Logger = _logger = new LoggerConfiguration()
   .WriteTo.File(
      new JsonFormatter(renderMessage: true),
      ApplicationData.Current.LocalCacheFolder.Path + "\\log.txt", 
      rollingInterval: RollingInterval.Minute)
      .MinimumLevel.Verbose()
      .CreateLogger();

References

File access permissions