Problem 32-bit executable - …installer.exe: Permission denied

TLDR: 32-bit executables with “install”, “setup” or “update” in their filename, when run from MSYS2 or Cygwin, will fail.

These same executables when run from PowerShell or the Command Prompt will pop up the “Do you want to allow this app from an unknown publisher to make changes to your device?” User Account Control. However this logic does not seem to be available in MSYS2/Cygwin, so in MSYS2/Cygwin you get a Permission Denied.



  1. Change the executable filename if that is possible.

  2. Run as Administrator

  3. Disable the “User Account Control: Detect application installations and prompt for elevation” policy setting. See

Problem - Sys_error(”…\_opam\lib\…: Permission denied”)

Partial Root Cause

TLDR: This is a known issue although it is not known what is triggering the problem.

#=== ERROR while installing dune-configurator.2.9.0 ===========================#
Sys_error("Z:\\source\\diskuv-ocaml-starter\\build\\dev\\Debug\\_opam\\lib\\dune-configurator\\.private\\configurator__Dune_lang.cmi: Permission denied")

The extended file access control lists (“ACLs”) are set incorrectly on your build directory (Z:\\source\\diskuv-ocaml-starter\\build\\dev\\Debug in the example) or one of its subdirectories.

This can be seen using a Cygwin session:

PS Z:\source\diskuv-ocaml-starter> & $env:DiskuvOCamlHome\tools\cygwin\bin\mintty.exe -
 1[DESKTOP-A ~]$ getfacl $(cygpath -au 'Z:\\source\\diskuv-ocaml-starter\\build\\dev\\Debug\\_opam\\lib\\dune-configurator\\.private\\configurator__Dune_lang.cmi')
 2> # file: /cygdrive/z/source/diskuv-ocaml-starter/build/dev/Debug/_opam/lib/dune-configurator/.private/configurator__Dune_lang.cmi
 3> # owner: you
 4> # group: you
 5> user::rwx
 6> group::rwx
 7> other::rwx
 9[DESKTOP-A ~]$ getfacl $(cygpath -au 'Z:\\source\\diskuv-ocaml-starter\\build\\dev\\Debug\\_opam\\lib\\dune-configurator\\.private')
10> # file: /cygdrive/z/source/diskuv-ocaml-starter/build/dev/Debug/_opam/lib/dune-configurator/.private
11> # owner: you
12> # group: you
13> user::rwx
14> group::rwx
15> other::rwx
16> default:user::---
17> default:group::---
18> default:other::rwx

The highlighted extended ACLs, in particular the default:user::--- entry, are removing permissions during OCaml builds.

A full root cause would say which Windows executable or script is inserting the extended ACLs. Cygwin is famous/notorious for adjusting the ACLs, but it may be anything including anti-malware software.


Launch a Cygwin session:

PS Z:\source\diskuv-ocaml-starter> & $env:DiskuvOCamlHome\tools\cygwin\bin\mintty.exe -

and then type the following (replacing the build directory with your own):

[DESKTOP-A ~]$ find "$(cygpath -au 'Z:\\source\\diskuv-ocaml-starter\\build\\dev\\Debug')" -print0 | xargs -0 --no-run-if-empty setfacl --remove-all --remove-default

Problem - vendor/diskuv-ocaml/runtime/unix/ No such file or directory

Root Cause

This is typically an indication that your git repository was not cloned with the recursive flag, as in:

git clone

instead of the correct:

git clone --recursive

When you leave out the --recursive option then Git will not fetch any of the submodules. Diskuv OCaml requires that you load it as a Git submodule.



git submodule update --init --recursive