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opam mingw repository

An opam repository for windows - including an experimental build of opam for windows (of course, you still need cygwin for nearly everything: a shell interpreter to run configure scripts, git, rsync, ...)


There is now a small homepage with installation instructions and usage information: - and a graphical installer that automates the steps listed below.


Esy also supports Windows. If you are not already familar with opam from Linux / OS X and don't want to change your habits, give it a try first.



The archives contain native versions of opam, flexdll and aspcud. They are all not linked against cygwin1.dll, so you can use them with either the 32-bit or 64-bit version of cygwin.


  • First install cygwin and a few additionals packages: rsync, patch, diffutils, curl, make, unzip, git, m4, perl, and of course mingw64-i686-gcc-core and/or mingw64-x86_64-gcc-core.

  • If your logon name contains whitespace characters (e.g. 'Firstname Lastname') or any other character that would require quoting inside a unix shell or cmd.exe, follow the instructions at

  • Then proceed inside a cygwin shell:

$ tar -xf 'opam32.tar.xz' # or tar -xf 'opam64.tar.xz'
$ bash opam32/  # --prefix /usr/foo, the default prefix is /usr/local
                          # maybe you have to add /usr/local/bin to your PATH
$ opam init default "" -c "ocaml-variants.4.07.1+mingw32" --disable-sandboxing
# or, if you prefer the 64-bit version - 'opam switch -a' will list other supported versions
$ opam init default "" -c "ocaml-variants.4.07.1+mingw64" --disable-sandboxing
$ eval $(ocaml-env cygwin)

Things to remember

  • Add /usr/i686-w64-mingw32/sys-root/mingw/bin (or /usr/x86_64-w64-mingw32/sys-root/mingw/bin) to your $PATH, if you use depext-cygwinports

  • Consider to use windows symlinks inside cygwin: export CYGWIN='winsymlinks:native'. Otherwise ocamlbuild and many build and test scripts will create symlinks, that are only understood by cygwin tools, but not by the OCaml compiler and other native windows programs. (Usually only adminstrators are allowed to create symlinks. But you can change the default settings, see this post for details)

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