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android.permission.WRITE_EXTERNAL_STORAGEis in AndroidManifest.xml. Also, add checks in your code to see if the storage is available to write before trying to write. And last: create a folder to put your files inside.
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libcore.io.ErrnoException: open failed: EBUSY (Device or resource busy)
at libcore.io.Posix.open(Native Method)