VVincent Bernardoff <firstname.lastname@example.org>
RRaja Boujbel <email@example.com>
KKate Deplaix <firstname.lastname@example.org>
RRoberto Di Cosmo <email@example.com>
TThomas Gazagnaire <firstname.lastname@example.org>
LLouis Gesbert <email@example.com>
FFabrice Le Fessant <Fabrice.Le_fessant@inria.fr>
AAnil Madhavapeddy <firstname.lastname@example.org>
GGuillem Rieu <email@example.com>
RRalf Treinen <firstname.lastname@example.org>
FFrederic Tuong <email@example.com>
Small standard library extensions, and generic system interaction modules used by opam.
Published: 22 Nov 2023
opam - A Package Manager for OCaml
Opam is a source-based package manager for OCaml. It supports multiple simultaneous compiler installations, flexible package constraints, and a Git-friendly development workflow.
Opam was created and is maintained by OCamlPro.
Compiling This Repo
Either from an existing opam installation, use
opam pin add opam-devel --dev, or:
Make sure you have the required dependencies installed:
OCaml >= 4.08 (or see below)
A C++ compiler (unless building without a solver, see
./configure. If you don't have the dependencies installed, this will locally take care of all OCaml dependencies for you (downloading them, unless you used the inclusive archive we provide for each release).
This is all you need for installing and using opam, but if you want to use the
opam-lib (to work on opam-related tools), you need to link it to installed libraries. It's easier to already have a working opam installation in this case, so you can do it as a second step.
Make sure to have
opam-file-formatinstalled. Or run
opam install . --deps-onlyif you already have a working instance. Re-run
make libinstallat the end
Note: If you install on your system (without changing the prefix), you will need to install as root (
sudo does not propagate environment variables, there will be some errors. You can use
sudo -E "PATH=$PATH" in order to ensure you have a good environment for install.
If you are developing opam, you may enable developer features by including the
--enable-developer-mode parameter with
Compiling on Native Windows
Cygwin (https://www.cygwin.com/setup-x86_64.exe) is always required to build opam on Windows.
The following Cygwin packages are required:
From Devel -
From Devel -
patch(not required if OCaml and all required packages are pre-installed)
From Devel -
From Devel -
From Devel -
mingw64-x86_64-gcc-g++(not required if building with MSVC)
Alternatively, having downloaded Cygwin's setup program, Cygwin can be installed using the following command line:
setup-x86_64 --root=C:\cygwin64 --quiet-mode --no-desktop --no-startmenu --packages=make,mingw64-i686-gcc-g++,mingw64-x86_64-gcc-g++,patch,autoconf,curl
--no-startmenu switches may be omitted in order to create shortcuts on the Desktop and Start Menu, respectively. Executed this way, setup will still be interactive, but the packages will have been preselected. To make setup fully unattended, choose a mirror URL from https://cygwin.com/mirrors.lst and add the
--site switch to the command line (e.g.,
It is recommended that you set the
CYGWIN environment variable to
Cygwin is started either from a shortcut or by running:
We recommended you build opam outside Cygwin's root (so in
/cygdrive/c/...). From an elevated Cygwin shell, edit
/etc/fstab and ensure that the file's content is exactly:
none /cygdrive cygdrive noacl,binary,posix=0,user 0 0
The change is the addition of the
noacl option to the mount instructions for
/cygdrive and this stops from Cygwin from attempting to emulate POSIX permissions over NTFS (which can result in strange and unnecessary permissions showing up in Windows Explorer). It is necessary to close and restart all Cygwin terminal windows after changing
Opam is able to be built without a preinstalled OCaml compiler. For the MSVC ports of OCaml, the Microsoft Windows SDK 7 or later or Microsoft Visual Studio is required (https://www.microsoft.com/en-gb/download/details.aspx?id=8442 - either x86 or x64 may be installed, as appropriate to your system). It is not necessary to modify PATH, INCLUDE, or LIB. Opam's build system will automatically detect the required changes.
If OCaml is not preinstalled, run:
make compiler [OCAML_PORT=mingw64|mingw|msvc64|msvc|auto]
OCAML_PORT variable determines which flavour of Windows OCaml is compiled;
auto will attempt to guess. As long as GCC is not installed in Cygwin (i.e., the native C compiler for Cygwin),
OCAML_PORT does not need to be specified and
auto will be assumed. Once the compiler is built, you may run:
to install the dependencies as
findlib packages to the compiler. Building
lib-pkg requires the ability to create native symbolic links (and the
CYGWIN variable must include
winsymlinks:native). This means that either Cygwin must be run elevated from an account with administrative privileges, or your user account must be granted the SeCreateSymbolicLinkPrivilege either by enabling Developer mode on Windows 10 or using Local Security Policy on earlier versions of Windows. Alternatively, you may run
configure and use vendored deps, as advised.
You can then
configure and build opam as above.
Compiling Without OCaml
make cold is provided as a facility to compile OCaml, then bootstrap opam. You don't need to run
./configure in that case, but you may specify
CONFIGURE_ARGS if needed. E.g.,:
make cold CONFIGURE_ARGS="--prefix ~/local"
NOTE: You'll still need GNU make.
Have a bug or a feature request? Please open an issue on our bug-tracker. Please search for existing issues before posting and include the output of
opam config report and any details that may help track down the issue.
The main documentation entry point to opam is the user manual, available using
opam --help. To get help for a specific command, use
opam <command> --help.
Guides and Tutorials
API, Code Documentation, and Developer Manual
A more thorough technical document describing opam and specifying the package description format is available in the developer manual.
make doc will otherwise make the API documentation available under
Keep track of development and community news.
Have a question that's not a feature request or bug report? Ask on the mailing list.
Chat with fellow opamers on IRC. On the
irc.libera.chatserver, in the
We welcome contributions! Please use GitHub's pull-request mechanism against the master branch of the opam repository. If that's not an option for you, you can use
git format-patch and email us.
The release cycle respects Semantic Versioning.
opam2web generates a collection of browsable HTML files for a given repository. It is used to generate http://opam.ocaml.org.
opam-rt is the regression framework for opam.
opam-publish is a tool to facilitate the creation, update, and publication of opam packages.
Copyright and license
The version comparison function in
src/core/opamVersionCompare.ml is part of the Dose library and Copyright 2011 Ralf Treinen.
All other code is:
Copyright 2012-2020 OCamlPro Copyright 2012 INRIA
All rights reserved. Opam is distributed under the terms of the GNU Lesser General Public License version 2.1, with the special exception on linking described in the file LICENSE.
Opam is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.