Re: Is the shell command "mv" atomic
From: Dragan Cvetkovic <d1r2a3g4a5n.NOSPAM@SPAM.t6h7t.net>
Date: 03 Apr 2003 10:54:30 -0500
Chris Lowth <email@example.com> writes:
> Andy Isaacson wrote:
> > mv(1) uses rename(2) to do its work. rename(2) is atomic. Therefore,
> > the race condition you describe cannot occur. Your script is safe.
> No: Not true for all Unixes - some have "rename" as a system, and for others
> "rename" is library call that uses link and unlink to do it's work.
> Under linux (for example) - "rename" is indeed a system call - but I
> wouldn't like to guarantee that this means that the action is atomic.
Well, POSIX requires it. Here is the quote from OpenGroup specification for
rename(2) (in Rationale):
This rename() function is equivalent for regular files to that defined
by the ISO C standard. Its inclusion here expands that definition to
include actions on directories and specifies behavior when the new
parameter names a file that already exists. That specification
requires that the action of the function be atomic.
Note the last sentence there.
To be or not to be is true. G. Boole No it isn't. L. E. J. Brouwer
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