ln -f

[David J. MacKenzie]

In article <1056 at undeed.UUCP> barrett at undeed.UUCP (Alan P. Barrett) writes:

> But that doesn't give the same result.  If you remove file2 first, then
> there is a brief window between the 'rm' and the 'ln' during which no
> file named file2 exists.  If you use a version of 'ln' that clobbers
> file2 and replaces it with a link to file1 in an atomic operation, there
> is no such window.  The difference might be important in some
> applications.

Wrong.  There is no way to clobber file2 and replace it with a hard
link in an atomic operation.  link(2) requires that the target file
not exist, otherwise it fails with:

     EEXIST		 The  link  referred  to  by  name2  does
			 exist.

Versions of ln that allow an existing target file remove it first with
unlink(2).  There is a *shorter* window during which file2 doesn't
exist than if rm(1) were used because there isn't the extra time of
starting up a new process in between the link and unlink operations,
but there *is* a window.
--
David J. MacKenzie <djm at eng.umd.edu> <djm at ai.mit.edu>