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I see log messages in azure iot device client source code like this: log.debug("Connection already opened by TransportClient."); or log.info("Device client opened successfully");

My question is where these log messages going? how to get that messages for debug purpose? Thanks

blueGrass29
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    This depends upon your platform. If you are running the C SDK on Linux or Windows these messages are routed to stdout. Hower there is a hook in the SDK that lets you send them wherever you want. I could help you more if you provide more detail about your platform. – Mark Radbourne Dec 27 '19 at 21:43
  • @MarkRadbourne where is the hook to send the C SDK logging to a place other than stdout? Is there a C SDK function I can call? – Timothy John Laird Aug 07 '20 at 14:32
  • @TimothyJohnLaird I haven't looked at this is in some time. Take a look at xlogging.h. There is a function declared in there called xlogging_set_log_function. You can find the file here: https://github.com/Azure/azure-c-shared-utility/blob/65c27eb4ab9a8bbe36b4d7c5a0e9ad305becb8b4/inc/azure_c_shared_utility/xlogging.h#L219 – Mark Radbourne Aug 07 '20 at 18:54

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In general, Blob Storage is added as a 'logging endpoint' which shall encompass a storage account, container in the account and blob in the container. The blobs of type 'Block blobs' shall be utilized for storing text and binary data.

All logs get stored in 'Block blobs' in a container named $logs, which is automatically created when Storage Analytics is enabled for a storage account. The $logs container is located in the blob namespace of the storage account, for example: http://.blob.core.windows.net/$logs

To view and analyze your log data, you should download the blobs that contain the log data you are interested in to a local machine. There are many tools like AzCopy, Azure Storage Data Movement library, Azure Import/Export service to import or export data to and from your storage account. To view the logs, you can also use any tool that can access Azure blob storage, such as Visual Studio or Cerebrata Azure Management Studio.

In case of azure-iot-sdk, each IoT hub exposes a set of endpoints(service endpoints) for the solution's back end to communicate with the devices. An IoT hub has a default built-in-endpoint (messages/events). By default, messages are routed to the built-in service-facing endpoint (messages/events) that is compatible with Event Hubs. You can refer to below link to various methods to read from built-in endpoint https://learn.microsoft.com/en-us/azure/iot-hub/iot-hub-devguide-messages-read-builtin

You can also create custom endpoints to route messages to by linking other services in your subscription to the IoT Hub. In case if the custom endpoint is created, a message is routed to multiple endpoints whose routing queries it matches. There are two storage services IoT Hub can route messages to Azure Blob Storage and ADLS (Azure Data Lake Storage) Gen2 accounts. You can refer to the below link to various methods to read from custom endpoint https://learn.microsoft.com/en-us/azure/iot-hub/iot-hub-devguide-messages-read-custom

In the scenario of logs from IoT SDK itself, the logs can get logged in stdout or stderr as per type of log and based on the deployment environment and also can be redirected accordingly as per the requirement. The SDK uses debug library for detailed logs. The below link can be helpful in giving additional details https://github.com/Azure/azure-iot-sdk-node/wiki/Troubleshooting-Guide-Devices

Karthik Balaguru
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