using Jupiter notebooks .ipynb created on Windows (Oracle VM virtual box) on sage, linux

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Hi

1) I use Jupiter notebooks .ipynb created on Windows (Oracle VM virtual box) at home, and would like to upload and use them on our linux sage installation, in our University

It seems this is impossible (upload of .ipynb is refused by linux sage)

2) As a substitute, I noticed on a notebook .sage created by someone else that it is at least pure text, and hence can be copied-pasted on a new file in the linux machine. Is it possible to convert my .ipynb notebooks to .sage notebooks? This would allow using them both as notebooks and as a source of copypaste when upload is refused. In fact, can .sage files be created on Windows (Oracle VM virtual box)?

Thanks, Florin