./ocamlopt.opt -nostdlib unix.cmxa -g -I stdlib -I otherlibs/unix  
ocamlbuild/ocamlbuild_executor.cmx ocamlbuild/ocamlbuild_pack.cmx  
ocamlbuild/ocamlbuild_unix_plugin.cmx ocamlbuild/ocamlbuild.cmx -o  
ocamlbuild/ocamlbuild.native
Undefined symbols:
   "_unix_setgroups", referenced from:
       _camlUnix__215 in unix.a(unix.o)
       _unix_setgroups$non_lazy_ptr in unix.a(unix.o)
   "_unix_initgroups", referenced from:
       _camlUnix__215 in unix.a(unix.o)
       _unix_initgroups$non_lazy_ptr in unix.a(unix.o)
ld: symbol(s) not found
collect2: ld returned 1 exit status
File "caml_startup", line 1, characters 0-1:
Error: Error during linking
Exit code 2 while executing this command:
   ./ocamlopt.opt -nostdlib unix.cmxa -g -I stdlib -I otherlibs/unix  
ocamlbuild/ocamlbuild_executor.cmx ocamlbuild/ocamlbuild_pack.cmx  
ocamlbuild/ocamlbuild_unix_plugin.cmx ocamlbuild/ocamlbuild.cmx -o  
ocamlbuild/ocamlbuild.native

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Mac hacker with a performance bent
http://linkedin.com/in/joelreymont