As I said earlier I don't have a Yun (or anything similar such as a Pi or a BeagleBone Black) so I have no means to try what you are talking about.
Thinking some more about the lack of Yun support I have been wondering is it wrong to think of it as a general purpose Linux computer. Perhaps it would be more correct to see it as having a very limited subset of Linux capabilities which were/are not intended to be enhanced.
@rmagnus I wonder if you have tried reading your file using Python on the Linino side. If that doesn't work there is surely a major flaw in the system.
But if it does work maybe the solution would be to have a Python program to handle the Linino side and communicate with the Arduino side. That's how you would have to do it with a regular PC and an Arduino.
...R