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Notice: Running the AWS IoT Device Client will incur usage of AWS IoT services, and is likely to incur charges on your AWS account. Please refer the pricing pages for AWS IoT Core, AWS IoT Device Management, and AWS IoT Device Defender for more details.

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Environment Variables

In addition to the application configuration settings described in Configuring the AWS IoT Device Client, the device client will also read from the environment variables listed below.

  • AWS_CRT_MEMORY_TRACING

    • The AWS C-runtime aka CRT supports capturing statistics about memory allocations at runtime.
    • This diagnostic information is made configurable by the device client through the AWS_CRT_MEMORY_TRACING environment variable.
    • When AWS_CRT_MEMORY_TRACING is unset or has the value 0, then no diagnostic information is captured by the CRT.
    • When AWS_CRT_MEMORY_TRACING=1 aka AWS_MEMTRACE_BYTES, then the CRT will collect information about the size and number of allocations.
    • When AWS_CRT_MEMORY_TRACING=2 aka AWS_MEMTRACE_STACKS, then the CRT will also collect the callstack for each allocation.
    • Sending the hangup signal SIGHUP to a running device client process when memory tracing is enabled will print the contents of the trace to the SDK log file.
    • The device client will also print the contents of the trace during shutdown when memory tracing is enabled.
    • When there are no pending allocations or memory trace is not enabled, then nothing is printed to the SDK log file.
    • Enabling memory allocation tracing has a nontrivial cost and we do not recommend that customers enable this by default for production deployments.

  • LOCK_FILE_PATH

    • To enforce single instance creation, device client writes a file to a specific directory. By default, the device client will write the lockfile to /run/lock/ and name it "devicecl.lock".
    • To override the default directory, set LOCK_FILE_PATH to a writable directory e.g. LOCK_FILE_PATH=/my/dir/. Permissions still apply when writing to restricted directories.
    • While this should in theory enforce a single instance of device client, double check with ps if device client is not starting properly.

  • AWSIOT_TUNNEL_ACCESS_TOKEN

    • The Secure Tunneling Feature allows customers to gain remote access to the device client.
    • When the secure tunneling feature is enabled, the device client will obtain the destination access token used to communicate with the secure tunnel proxy by listening for a notification on an MQTT topic. More details are available at Secure Tunneling Feature.
    • The AWSIOT_TUNNEL_ACCESS_TOKEN environment variable can be used to inject the destination access token in situations where listening for the notification on an MQTT topic is disabled.
    • Since the destination access token has a limited lifetime and will change each time a new secure tunnel is provisioned, using AWSIOT_TUNNEL_ACCESS_TOKEN to pass the destination access token is strictly for debugging purposes and not recommended for production deployments.

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