MQTT Persistent Session Not Supported

The broker does not support persistent sessions.

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What is

MQTT Persistent Session Not Supported

?

Understanding MQTT and Its Purpose

MQTT, which stands for Message Queuing Telemetry Transport, is a lightweight messaging protocol designed for constrained devices and low-bandwidth, high-latency, or unreliable networks. It is widely used in IoT (Internet of Things) applications for its efficiency and ease of use. MQTT operates on a publish/subscribe model, allowing devices to communicate asynchronously.

Identifying the Symptom: Persistent Session Not Supported

When working with MQTT, you might encounter an issue where the broker does not support persistent sessions. This symptom is typically observed when clients attempt to connect with the 'clean session' flag set to false, expecting the broker to retain session information across disconnections, but instead, the session data is lost.

What is a Persistent Session?

A persistent session in MQTT allows the broker to store session information, such as subscriptions and undelivered messages, even when the client disconnects. This feature is crucial for applications where message continuity and reliability are important.

Exploring the Issue: Why Persistent Sessions May Not Be Supported

The root cause of this issue is often that the MQTT broker is not configured to support persistent sessions. Some brokers may have this feature disabled by default, or it might not be supported at all, depending on the broker's implementation.

Common Scenarios

The broker's configuration file does not enable persistent sessions.
The broker version in use does not support persistent sessions.
Client settings are incorrectly configured, leading to session data not being retained.

Steps to Resolve the Issue

To address the issue of persistent sessions not being supported, follow these steps:

Step 1: Verify Broker Configuration

Check the broker's configuration file to ensure that persistent sessions are enabled. This often involves setting a specific parameter in the configuration file. For example, in Mosquitto, you might need to set persistent_client_expiration to a non-zero value.

Step 2: Update Broker Software

If the broker version does not support persistent sessions, consider upgrading to a newer version that includes this feature. Refer to the broker's documentation for upgrade instructions. For instance, Eclipse Paho provides comprehensive guides for upgrading.

Step 3: Adjust Client Settings

Ensure that the client is configured correctly to request a persistent session. This involves setting the 'clean session' flag to false when connecting to the broker. Here's an example in Python using the Paho MQTT client:

import paho.mqtt.client as mqtt client = mqtt.Client(clean_session=False) client.connect("broker.hivemq.com", 1883, 60) client.loop_start()

Conclusion

By ensuring that your MQTT broker is configured to support persistent sessions and that your client settings are correct, you can effectively resolve the issue of persistent sessions not being supported. For further reading, consider exploring the official MQTT documentation for more in-depth information on session management and broker configurations.

Attached error:

MQTT Persistent Session Not Supported

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The SSL/TLS handshake between client and server failed.

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The broker did not acknowledge the publish request.

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A network error occurred, disrupting the connection between client and server.

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The MQTT broker is not available or not reachable.

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The client is not authorized to connect to the broker.

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The client is using an MQTT protocol version that the server does not support.

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The client did not receive a response from the server within the expected time frame.

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Authentication failed due to incorrect username or password.

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The client identifier is malformed or not accepted by the server.

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