/usr/share/lilypond/2.16.2/ly/generate-interface-doc-init.ly is in lilypond-data 2.16.2-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | \version "2.16.0"
%
% Running LilyPond on this file generates the short interface doc
%
#(eval-string (ly:gulp-file "generate-interface-doc.scm"))
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