3.5. Setting the Log Level of the Server

If the functions call the slapi_log_error() function to write messages to the error log, you need to make sure that the Directory Server is configured to log messages with the severity level that you have specified. The available severity levels are fully documented in Part IV, “Function Reference”.
For example, suppose you call this function in the plug-in:
slapi_log_error( SLAPI_LOG_PLUGIN, "searchdn_preop_init", "Plug-in successfully registered.\n" );
You need to make sure that the Directory Server is configured to log messages with the severity level SLAPI_LOG_PLUGIN. Error logging is controlled with the nsslapd-errorlog-level attribute in cn=config.