ArcGIS Server records system messages in log files. When you suspect something isn't working right, you can examine the log files to see exactly what is happening with your GIS server.
You can specify where the server writes its log files, or simply accept the default location in the ArcGIS Server installation directory, which is <ArcGIS Server Install directory>\Server\user\log on the SOM machine.
If you're configuring a distributed installation of ArcGIS Server (where components of the server run on more than one machine), you will need to share the log directory and reference it using a UNC path (for example, \\myServer\log) You'll also need to make sure the SOM and SOC Accounts have Read and Write permissions to the log directory.
Set the logging level:
0-No logging