# 13.1. Prerequisites

## 13.1.1. Compilers

Although it should probably be assumed, you’ll need a C compiler that supports C99.

You’ll also need a Fortran compiler if you want to build the Fortran MPI bindings (the more recent the Fortran compiler, the better), and a Java compiler if you want to build the (unofficial) Java MPI bindings.

## 13.1.2. GNU Autotools

When building Open MPI from its repository sources, the GNU Autotools must be installed (i.e., GNU Autoconf, GNU Automake, and GNU Libtool).

Tool | Minimum version
--- | ---
Autoconf | 2.69.0
Automake | 1.13.4
Libtool | 2.4.2

Note

The GNU Autotools are not required when building Open MPI from distribution tarballs. Open MPI distribution tarballs are bootstrapped such that end-users do not need to have the GNU Autotools installed.

You can generally install GNU Autoconf, Automake, and Libtool via your Linux distribution native package system, or via Homebrew or MacPorts on MacOS. This usually “just works.”

If you run into problems with the GNU Autotools, or need to download / build them manually, see the how to build and install GNU Autotools section for much more detail.

## 13.1.3. Perl

Open MPI still uses Perl for a few of its build scripts (most notably, `autogen.pl`).

Generally speaking, any recent-ish release of Perl 5 should be sufficient to correctly execute Open MPI’s Perl scripts.

## 13.1.4. Flex

Minimum supported version: 2.5.4.

Flex is used during the compilation of a developer’s checkout (it is not used to build official distribution tarballs). Other flavors of lex are not supported: given the choice of making parsing code portable between all flavors of lex and doing more interesting work on Open MPI, we greatly prefer the latter.

Note that no testing has been performed to see what the minimum version of Flex is required by Open MPI. We suggest that you use v2.5.35 at the earliest.

For now, Open MPI will allow developer builds with Flex 2.5.4. This is primarily motivated by the fact that RedHat/CentOS 5 ships with Flex 2.5.4. It is likely that someday Open MPI developer builds will require Flex version >=2.5.35.

Note that the `flex`-generated code generates some compiler warnings on some platforms, but the warnings do not seem to be consistent or uniform on all platforms, compilers, and flex versions. As such, we have done little to try to remove those warnings.

If you do not have Flex installed and cannot easily install it via your operating system’s packaging system (to include Homebrew or MacPorts on MacOS), see the Flex Github repository.

## 13.1.5. Sphinx (and therefore Python)

Sphinx is a Python-based tool used to generate both the HTML version of the documentation (that you are reading right now) and the nroff man pages.

Official Open MPI distribution tarballs contain pre-built HTML documentation and man pages. This means that — similar to the GNU Autotools — end users do not need to have Sphinx installed, but will still have both the HTML documentation and man pages installed as part of the normal configure / build / install process.

However, the HTML documentation and man pages are not stored in Open MPI’s Git repository; only the ReStructred Text source code of the documentation is in the Git repository. Hence, if you are building Open MPI from a Git clone, you will need Sphinx (and some Python modules) in order to build the HTML documentation and man pages.

Important

Most systems do not have Sphinx and/or the required Python modules installed by default. See the Installing Sphinx section for details on how to install Sphinx and the required Python modules.

If `configure` is able to find Sphinx and the required Python modules, it will automatically generate the HTML documentation and man pages during the normal build procedure (i.e., during `make all`). If `configure` is not able to find Sphinx and/or the required Python modules, it will simply skip building the documentation.

Note

If you have built/installed Open MPI from a Git clone and unexpectedly did not have the man pages installed, it is likely that you do not have Sphinx and/or the required Python modules available.

See the Installing Sphinx section for details on how to install Sphinx and the required Python modules.

Important

`make dist` will fail if `configure` did not find Sphinx and/or the required Python modules. Specifically: if `make dist` is not able to generate the most up-to-date HTML documentation and man pages, you cannot build a distribution tarball. This is an intentional design decision.