/usr/share/emacs24/site-lisp/subdirs.el is in emacs24-common 24.3+1-2ubuntu1.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | (if (fboundp 'normal-top-level-add-subdirs-to-load-path)
(normal-top-level-add-subdirs-to-load-path))
|