It looks like a side effect of Printf.printf.  Try prerr_endline 
(Printf.sprintf "Hi! %d\n" (getpid ())) instead.

Michael wrote:

>Hi,
>
>I don't understand why this:
>
>open Unix;;
>let _ = 
>	Printf.printf "Hi! %d\n" (getpid());
>	match fork() with
>	| 0 -> if fork() <> 0 then exit 0;
>	       ()
>	| id -> ignore (waitpid [] id)
>
>prints out that:
>Hi! 12215
>Hi! 12215
>Hi! 12215
>
>
>with ocaml 3.08.2. Any hints?
>
> Michael
>
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>
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