Today in POSIX surprises: `ln -f` is not *quite* atomic due to the combined semantics of link() and rename(); it racily uses a temp file and if the stars align might unlink() an identially-named temp file created by another process.
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Sounds like a TOCTTOU waiting to happen
Predicting the filename is not terribly likely (it seems to use entropy from urandom). Just one of those "might break a production system somewhere some day when the stars align" things.
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Ahh fair. I’m just wondering what happens if the file reappears in the middle (or can that not happen?)
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That's the bug. ln -f does link(src, tmp); rename(tmp, dst); unlink(tmp). It can't just link() because that doesn't clobber; it has to unlink() because rename() is a successful noop (!) if both sides are the same inode. But if they aren't and someone re-creates tmp it gets nuked.
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