capistrano/capistrano — pull request #460 by johnbellone (2013-04-26 01:11:56+00:00)
Title: Fixes #346 by using ln and then mv.

After reading several articles it seems the mv UNIX operation is atomic,
but the creation
of a symbolic link is not. This is a way that we can be sure that there
is no gap between
the previous release and the current release.

http://stackoverflow.com/questions/1385244/replace-important-symbolic-link-safely