Autotools is a GNU build system that provides a build-script generator. By running the platform-independent ./configure script that comes with the package, you can generate a platform-dependent Makefile.


The AutotoolsPackage base class comes with the following phases:

  1. autoreconf - generate the configure script
  2. configure - generate the Makefiles
  3. build - build the package
  4. install - install the package

Most of the time, the autoreconf phase will do nothing, but if the package is missing a configure script, autoreconf will generate one for you.

The other phases run:

$ ./configure --prefix=/path/to/installation/prefix
$ make
$ make check  # optional
$ make install
$ make installcheck  # optional

Of course, you may need to add a few arguments to the ./configure line.

Important files

The most important file for an Autotools-based package is the configure script. This script is automatically generated by Autotools and generates the appropriate Makefile when run.


Watch out for fake Autotools packages!

Autotools is a very popular build system, and many people are used to the classic steps to install a package:

$ ./configure
$ make
$ make install

For this reason, some developers will write their own configure scripts that have nothing to do with Autotools. These packages may not accept the same flags as other Autotools packages, so it is better to use the Package base class and create a custom build system. You can tell if a package uses Autotools by running ./configure --help and comparing the output to other known Autotools packages. You should also look for files like:


Packages that don’t use Autotools aren’t likely to have these files.

Build system dependencies

Whether or not your package requires Autotools to install depends on how the source code is distributed. Most of the time, when developers distribute tarballs, they will already contain the configure script necessary for installation. If this is the case, your package does not require any Autotools dependencies.

However, a basic rule of version control systems is to never commit code that can be generated. The source code repository itself likely does not have a configure script. Developers typically write (or auto-generate) a script that contains configuration preferences and a script that contains build instructions. Then, autoconf is used to convert into configure, while automake is used to convert into is used by configure to generate a platform-dependent Makefile for you. The following diagram provides a high-level overview of the process:

If a configure script is not present in your tarball, you will need to generate one yourself. Luckily, Spack already has an autoreconf phase to do most of the work for you. By default, the autoreconf phase runs:

$ libtoolize
$ aclocal
$ autoreconf --install --verbose --force

All you need to do is add a few Autotools dependencies to the package. Most stable releases will come with a configure script, but if you check out a commit from the develop branch, you would want to add:

depends_on('autoconf', type='build', when='@develop')
depends_on('automake', type='build', when='@develop')
depends_on('libtool',  type='build', when='@develop')
depends_on('m4',       type='build', when='@develop')

In some cases, developers might need to distribute a patch that modifies one of the files used to generate configure or In this case, these scripts will need to be regenerated. It is preferable to regenerate these manually using the patch, and then create a new patch that directly modifies configure. That way, Spack can use the secondary patch and additional build system dependencies aren’t necessary.


If for whatever reason you really want to add the original patch and tell Spack to regenerate configure, you can do so using the following setting:

force_autoreconf = True

This line tells Spack to wipe away the existing configure script and generate a new one. If you only need to do this for a single version, this can be done like so:

def force_autoreconf(self):
    return self.version == Version('1.2.3'):

Finding configure flags

Once you have a configure script present, the next step is to determine what option flags are available. These flags can be found by running:

$ ./configure --help

configure will display a list of valid flags separated into some or all of the following sections:

  • Configuration
  • Installation directories
  • Fine tuning of the installation directories
  • Program names
  • X features
  • System types
  • Optional Features
  • Optional Packages
  • Some influential environment variables

For the most part, you can ignore all but the last 3 sections. The “Optional Features” sections lists flags that enable/disable features you may be interested in. The “Optional Packages” section often lists dependencies and the flags needed to locate them. The “environment variables” section lists environment variables that the build system uses to pass flags to the compiler and linker.

Addings flags to configure

For most of the flags you encounter, you will want a variant to optionally enable/disable them. You can then optionally pass these flags to the configure call by overriding the configure_args function like so:

def configure_args(self):
    args = []

    if '+mpi' in self.spec:

    return args

Note that we are explicitly disabling MPI support if it is not requested. This is important, as many Autotools packages will enable options by default if the dependencies are found, and disable them otherwise. We want Spack installations to be as deterministic as possible. If two users install a package with the same variants, the goal is that both installations work the same way. See here and here for a rationale as to why these so-called “automagic” dependencies are a problem.

By default, Autotools installs packages to /usr. We don’t want this, so Spack automatically adds --prefix=/path/to/installation/prefix to your list of configure_args. You don’t need to add this yourself.

Helper functions

You may have noticed that most of the Autotools flags are of the form --enable-foo, --disable-bar, --with-baz=<prefix>, or --without-baz. Since these flags are so common, Spack provides a couple of helper functions to make your life easier.

TODO: document with_or_without and enable_or_disable.

Configure script in a sub-directory

Occasionally, developers will hide their source code and configure script in a subdirectory like src. If this happens, Spack won’t be able to automatically detect the build system properly when running spack create. You will have to manually change the package base class and tell Spack where the configure script resides. You can do this like so:

configure_directory = 'src'

Building out of source

Some packages like gcc recommend building their software in a different directory than the source code to prevent build pollution. This can be done using the build_directory variable:

build_directory = 'spack-build'

By default, Spack will build the package in the same directory that contains the configure script

Build and install targets

For most Autotools packages, the usual:

$ configure
$ make
$ make install

is sufficient to install the package. However, if you need to run make with any other targets, for example, to build an optional library or build the documentation, you can add these like so:

build_targets = ['all', 'docs']
install_targets = ['install', 'docs']


Autotools-based packages typically provide unit testing via the check and installcheck targets. If you build your software with spack install --test=root, Spack will check for the presence of a check or test target in the Makefile and run make check for you. After installation, it will check for an installcheck target and run make installcheck if it finds one.

External documentation

For more information on the Autotools build system, see: