The log output is stored in a file or can be displayed in the console. When the Unity Player initializes, any initial errors are logged in the console through stderr. If any initialization error occurs, Unity Player stops running with an error exit code.
By default, Unity writes standard log output into a log file located in your current home directory at ~/.config/unity3d/CompanyName/ProductName/Player.log. You can customize this path via the Player Data Path setting (menu: Player Settings > Other Settings > Configuration > Player Data path) or using the command line arguments.
If the standard log output fails to initialize, Unity writes the log output to the console.