# Miscelaneous

{% hint style="success" %}
Usually, you'll want to subscribe to a widcard topic like **downlink/#**.
{% endhint %}

## Reboot Device

Reboot can be triggered using `Device Menu -> Reboot`.

You will get a message on **downlink/reboot** topic, with an empty payload.

```bash
mosquitto_sub -h blynk.cloud -p 8883 -u device -P '{DEVICE_TOKEN}' -t 'downlink/reboot'
```

## Ping Device

This feature is activated using `Device Menu -> Ping`.

The server publishes **downlink/ping** topic, with `QOS 1` and an empty payload. Subsequently, the client should automatically respond with an MQTT `PUBACK` packet, in accordance with the MQTT standard.

```bash
mosquitto_sub -h blynk.cloud -p 8883 -u device -P '{DEVICE_TOKEN}' -t 'downlink/ping'
```

## Reconfigure Device

This feature is activated using a `Device -> Info Icon -> Three dots -> Reconfigure` button in the mobile application (see the [Mobile App Device Actions menu section](/en/blynk.apps/overview.md#device-actions-menu)).

The server publishes the downlink/reconfigure topic with an empty payload. Subsequently, the device should enter the Wi-Fi configuration stage, by broadcasting a Wi-Fi Access Point and asking the user to enter the new Wi-Fi network credentials.

```bash
mosquitto_sub -h blynk.cloud -p 8883 -u device -P '{DEVICE_TOKEN}' -t 'downlink/reconfigure'
```

## Last Will and Testament

Upon connection, the client can specifiy the Last Will message along with the topic to which it should be published. If the client loses connection **without sending a proper MQTT `DISCONNECT` message**, the broker will publish this pre-determined Last Will message.

## Server Diagnostics

The server has the capability to publish messages under the **downlink/diag** topic under certain circumstances, typically when it detects potentially problematic behavior from the client. These diagnostic messages are designed to be observed and addressed by developers.

```bash
mosquitto_sub -h blynk.cloud -p 8883 -u device -P '{DEVICE_TOKEN}' -t 'downlink/diag'
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.blynk.io/en/blynk.cloud-mqtt-api/device-mqtt-api/miscelaneous.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.