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OPAM is a source-based package manager for OCaml. It supports multiple simultaneous compiler installations, flexible package constraints, and a Git-friendly development workflow.
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OPAM - A package manager for OCaml

OPAM is a package manager for OCaml, based on the CUDF and the Dose libraries developped by the Mancoosi project, which are, among other things, used by Debian to manage their packages.


  • ocaml
  • curl or wget
  • git
  • rsync

Compiling OPAM

To compile opam, simply run:

$ ./configure # (or ./configure --prefix=$HOME if you want to install under your $HOME)
$ make

This will fetch the necessary archives if they are not already downloaded and then build OPAM. If you just want to get the necessary dependencies without compiling the project, run make clone.

If you don't have curl installed on your system, you can run make FETCH=wget clone before make.

Installing OPAM

To install opam simply run:

$ make install


$ sudo make install

if you need root privileges.

This way, opam binaries will be installed in $prefix/bin, where prefix might have been specified during the ./configure phase.

Using opam

All of the OPAM state is held in the ~\.opam directory in your home directory, including compiler installations. You should never need to switch to a root user to install packages. Package listings are obtained through remote sources.

$ opam init
$ eval `opam config -env`

The first command creates ~\.opam and set-up as default repository. The second command updates your local environment to use the packages installed by OPAM. For convenience, you can add this line in your ~/.profile.

$ opam list

As expected, this command lists all the available packages. We can now install some packages (for instance lwt):

$ opam install lwt

OPAM is able to track optional dependencies. This mean that installing an optional dependency of a package will recompile the package and all its forward dependencies. For instance:

$ opam install react

will install react, will recompile lwt (with the right ./configure options) and all the packages which depend on lwt.

Installing on other OCaml compiler

OPAM also manages meta-data about OCaml compilers. So in order to install a new version of the compiler, you can run:

$ opam switch 4.00.0
$ eval `opam config -env`

The first command will download and install ocaml-4.00.0, and the second command will update the environment variables. You can then install packages -- they will be installed on a different under ~/.opam/4.00.0.

In order to come-back to the system-wide OCaml installation, simply run:

$ opam switch system
$ eval `opam config -env`

You can use opam switch -list to display the list of available compilers.

Version pinning

$ opam pin <package> </local/path>

This command will use the content of </local/path> to compile <package>. This means that the next time you will do opam install <package>, the compilation process will be using a mirror of </local/path> instead of downloading the archive. This also means that any modification to </local/path> will be picked up by opam update, and thus opam upgrade will recompile <package> (and its forward dependencies) if needed.

To unpin a package, simply run:

$ opam pin <package> none

You can also pin a package to a specific version: opam pin <package> <version>


OPAM supports multiple repositories.

$ opam remote -list


shell/ contains shell-scripts to add auto-completion to OPAM. The script is not installed by default, so to activate the mode you can either:

  • move it at the right location (depending on your OS, for instance /etc/auto-complete.d/opam on Debian)

  • copy it somewhere in you path and source it in your .profile.


Some technical documentation is available in doc:

  • the API is available in doc/html/
  • The design documents are available in doc/specs/
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