About the message "Warning: Invalid DFU suffix signature" [HC-1426] (#503)

Various improvements

Author: seaxwi

content/Hardware Support/Portenta Family/About-the-Invalid-DFU-suffix-signature-warning-from-dfu-util.md

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+---
+title: About the "Invalid DFU suffix signature" warning from dfu-util
+id: 4411327110674
+---
+
+When uploading a sketch you may see this warning in the console output:
+
+```
+Warning: Invalid DFU suffix signature
+A valid DFU suffix will be required in a future dfu-util release
+```
+
+The message is informational and **does not** indicate a failed a failed upload or error.
+
+---
+
+## About the warning message
+
+The warning message is generated by dfu-util, a program used to upload sketches to some Arduino boards. The **DFU suffix** is a small block of data appended to the end of a firmware file that can be used to verify the firmware's integrity and compatibility with the target device.
+
+While a DFU suffix is recommended by the DFU standard and might become mandatory in a future version of dfu-util, it's not currently required for successful flashing. The version of dfu-util used for sketch uploads is [defined in the Arduino board platform](https://arduino.github.io/arduino-cli/0.19/package_index_json-specification). Any future version of dfu-util would only be adopted after verifying compatibility with the board platform.
+
+Currently, there is no way to prevent the warning from being displayed.
+
+---
+
+## How to tell if the sketch was uploaded
+
+If you see the lines `Download  [=========================] 100%`and `Download done`, it indicates that the sketch was uploaded to your board. This may be followed by a few lines of additional information, which can vary depending on the board. For example, a successful sketch upload to Arduino Portenta H7 completes with this console output:
+
+```
+...
+Download    [=======================  ]  93%       147456 bytes
+Download    [======================== ]  96%       151552 bytes
+Download    [=========================] 100%       156956 bytes
+Download done.
+File downloaded successfully
+Transitioning to dfuMANIFEST state
+```
+
+If the sketch upload fails, this will be indicated by other messages:
+
+* For `Failed uploading: uploading error: exit status 74`, see [dfu-util errors when uploading (exit status 74)](https://support.arduino.cc/hc/en-us/articles/11011849739804-dfu-util-errors-when-uploading-exit-status-74).
+* For `Compilation error: <error description>`, see [If your sketch doesn't compile](https://support.arduino.cc/hc/en-us/articles/4402764401554-If-your-sketch-doesn-t-compile).
+
+For general troubleshooting of uploads, see [If your sketch doesn't upload](https://support.arduino.cc/hc/en-us/articles/4403365313810-If-your-sketch-doesn-t-upload).
+
+---
+
+## Further reading
+
+* [dfu-util (sourceforge.net)](https://dfu-util.sourceforge.net/)
+* [dfu-suffix manual](https://dfu-util.sourceforge.net/dfu-suffix.1.html)