Sounds like a TOCTTOU waiting to happen
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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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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I've been repeatedly surprised by the number of colleagues who believe that link(2) and/or symlink(2) will atomically overwrite an existing file, without needing to unlink(2) the target and thus open the attendant race condition.
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Well you can rename() over the target, and that works perfectly well for symlinks. The problem is that rename() has a stupidly defined corner case where it returns *successfully* and yet *does nothing* when both sides are the same inode. And that opens up another race.
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there's a weird cheat in GNU land using ln and mv to do atomic replacement. I can never tell where it's used.
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It seems like Unix system calls are full of this kind of terrible design overall, and the POSIX spec has a lot of skeletons in its closet :(
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Not helped by all the people who think POSIX is God's gift to the world and shouldn't be changed/should be changed as little as possible
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did I ever tell you about the time when MinGW's ld could (and regularly did) have temp filename collisions with another ld executing in the same directory at the same time
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oh actually it was ar, not ld: basically their implementation of mkstemp() would call _open() with _O_TEMPORARY, which is the "delete on close" flag; ar then close()s the fd it gets from mktemp() and reopens the path with different flags
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UNIX has a lot of BS like this that make it unreliable sometimes.
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