[fsckboy]

the type of atomicity I've always seen it used for is, two processes try to rename a file at the same time, only one will succeed; the winner does what they planned and then rename the file back.

I guess you shouldn't ignore the error with both processes using the same destination name, why folks generally tend to put their pid in the lockfilename

[yencabulator]

Umm, two concurrent rename(2) syscalls to the same destination path will likely both succeed. One of them will win (not be overwritten), but both should succeed.

If you want atomic creation of a path, where no one else can succeed also, you want link(2) not rename(2).