Question

When a file is closed using close() or fclose() (for example), does Linux guarantee that the file is written back to (persistent) disc?

What I mean is, if close() returns 0 and then immediately afterwards the power fails, are previously written data guaranteed to persist, i.e. be durable?

The fsync() system call does provide this guarantee. Is closing a file also sufficient?

I can’t find anything which makes any claim one way or another at the moment.

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Question 2:

If close() does implicitly do an fsync(), is there a way of telling it not to?

Answer 1

From ‘man 2 close‘:

A successful close does not guarantee that the data has been successfully saved to disk, as the kernel defers writes.

The man page says that if you want to be sure that your data are on disk, you have to use fsync() yourself.