Getting Started

System Prerequisites

Spack has the following minimum system requirements, which are assumed to be present on the machine where Spack is run:

System prerequisites for Spack


Supported Versions


Requirement Reason



Interpreter for Spack

C/C++ Compilers

Building software


Build software


Extract/create archives


Compress/Decompress archives


Compress/Decompress archives


Compress/Decompress archives


Compress/Decompress archives



Compress/Decompress archives


Create/Use Buildcaches


Linux: identify operating system version


Sign/Verify Buildcaches


Manage Software Repositories



Manage Software Repositories



Manage Software Repositories

Python header files

Optional (e.g. python3-dev on Debian)

Bootstrapping from sources

These requirements can be easily installed on most modern Linux systems; on macOS, the Command Line Tools package is required, and a full XCode suite may be necessary for some packages such as Qt and apple-gl. Spack is designed to run on HPC platforms like Cray. Not all packages should be expected to work on all platforms.

A build matrix showing which packages are working on which systems is shown below.

apt update
apt install build-essential ca-certificates coreutils curl environment-modules gfortran git gpg lsb-release python3 python3-distutils python3-venv unzip zip
dnf install epel-release
dnf group install "Development Tools"
dnf install curl findutils gcc-gfortran gnupg2 hostname iproute redhat-lsb-core python3 python3-pip python3-setuptools unzip python3-boto3
brew update
brew install curl gcc git gnupg zip


Getting Spack is easy. You can clone it from the github repository using this command:

$ git clone -c feature.manyFiles=true

This will create a directory called spack.

Shell support

Once you have cloned Spack, we recommend sourcing the appropriate script for your shell:

# For bash/zsh/sh
$ . spack/share/spack/

# For tcsh/csh
$ source spack/share/spack/setup-env.csh

# For fish
$ . spack/share/spack/

That’s it! You’re ready to use Spack.

Sourcing these files will put the spack command in your PATH, set up your MODULEPATH to use Spack’s packages, and add other useful shell integration for certain commands, environments, and modules. For bash and zsh, it also sets up tab completion.

In order to know which directory to add to your MODULEPATH, these scripts query the spack command. On shared filesystems, this can be a bit slow, especially if you log in frequently. If you don’t use modules, or want to set MODULEPATH manually instead, you can set the SPACK_SKIP_MODULES environment variable to skip this step and speed up sourcing the file.

If you do not want to use Spack’s shell support, you can always just run the spack command directly from spack/bin/spack.

When the spack command is executed it searches for an appropriate Python interpreter to use, which can be explicitly overridden by setting the SPACK_PYTHON environment variable. When sourcing the appropriate shell setup script, SPACK_PYTHON will be set to the interpreter found at sourcing time, ensuring future invocations of the spack command will continue to use the same consistent python version regardless of changes in the environment.

Bootstrapping clingo

Spack uses clingo under the hood to resolve optimal versions and variants of dependencies when installing a package. Since clingo itself is a binary, Spack has to install it on initial use, which is called bootstrapping.

Spack provides two ways of bootstrapping clingo: from pre-built binaries (default), or from sources. The fastest way to get started is to bootstrap from pre-built binaries.

The first time you concretize a spec, Spack will bootstrap automatically:

$ spack spec zlib
==> Bootstrapping clingo from pre-built binaries
==> Fetching
==> Fetching
==> Installing "clingo-bootstrap@spack%gcc@10.2.1~docs~ipo+python+static_libstdcpp build_type=Release arch=linux-centos7-x86_64" from a buildcache
==> Bootstrapping patchelf from pre-built binaries
==> Fetching
==> Fetching
==> Installing "patchelf@0.16.1%gcc@10.2.1 ldflags="-static-libstdc++ -static-libgcc"  build_system=autotools arch=linux-centos7-x86_64" from a buildcache
Input spec

zlib@1.2.13%gcc@9.4.0+optimize+pic+shared build_system=makefile arch=linux-ubuntu20.04-icelake

If for security concerns you cannot bootstrap clingo from pre-built binaries, you have to disable fetching the binaries we generated with Github Actions.

$ spack bootstrap disable github-actions-v0.4
==> "github-actions-v0.4" is now disabled and will not be used for bootstrapping
$ spack bootstrap disable github-actions-v0.3
==> "github-actions-v0.3" is now disabled and will not be used for bootstrapping

You can verify that the new settings are effective with:

$ spack bootstrap list
Name: github-actions-v0.5 ENABLED

  Type: buildcache


    Buildcache generated from a public workflow using Github Actions.
    The sha256 checksum of binaries is checked before installation.

Name: github-actions-v0.4 ENABLED

  Type: buildcache


    Buildcache generated from a public workflow using Github Actions.
    The sha256 checksum of binaries is checked before installation.

Name: spack-install ENABLED

  Type: install


    Specs built from sources downloaded from the Spack public mirror.


When bootstrapping from sources, Spack requires a full install of Python including header files (e.g. python3-dev on Debian), and a compiler with support for C++14 (GCC on Linux, Apple Clang on macOS) and static C++ standard libraries on Linux.

Spack will build the required software on the first request to concretize a spec:

$ spack spec zlib
[+] /usr (external bison-3.0.4-wu5pgjchxzemk5ya2l3ddqug2d7jv6eb)
[+] /usr (external cmake-3.19.4-a4kmcfzxxy45mzku4ipmj5kdiiz5a57b)
[+] /usr (external python-3.6.9-x4fou4iqqlh5ydwddx3pvfcwznfrqztv)
==> Installing re2c-1.2.1-e3x6nxtk3ahgd63ykgy44mpuva6jhtdt
[ ... ]
zlib@1.2.11%gcc@10.1.0+optimize+pic+shared arch=linux-ubuntu18.04-broadwell

The Bootstrap Store

All the tools Spack needs for its own functioning are installed in a separate store, which lives under the ${HOME}/.spack directory. The software installed there can be queried with:

$ spack -b find
-- linux-ubuntu18.04-x86_64 / gcc@10.1.0 ------------------------
clingo-bootstrap@spack  python@3.6.9  re2c@1.2.1

In case it’s needed the bootstrap store can also be cleaned with:

$ spack clean -b
==> Removing bootstrapped software and configuration in "/home/spack/.spack/bootstrap"

Check Installation

With Spack installed, you should be able to run some basic Spack commands. For example:

$ spack spec netcdf-c
Input spec
 -   netcdf-c

 -   netcdf-c@4.9.2%gcc@11.4.0+blosc~byterange~dap~fsync~hdf4~jna+mpi~nczarr_zip+optimize~parallel-netcdf+pic+shared+szip+zstd build_system=autotools patches=0161eb8 arch=linux-ubuntu22.04-skylake_avx512
 -       ^bzip2@1.0.8%gcc@11.4.0~debug~pic+shared build_system=generic arch=linux-ubuntu22.04-skylake_avx512
 -           ^diffutils@3.10%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -               ^libiconv@1.17%gcc@11.4.0 build_system=autotools libs=shared,static arch=linux-ubuntu22.04-skylake_avx512
 -       ^c-blosc@1.21.5%gcc@11.4.0+avx2~ipo build_system=cmake build_type=Release generator=make arch=linux-ubuntu22.04-skylake_avx512
 -           ^cmake@3.27.9%gcc@11.4.0~doc+ncurses+ownlibs build_system=generic build_type=Release arch=linux-ubuntu22.04-skylake_avx512
 -               ^curl@8.6.0%gcc@11.4.0~gssapi~ldap~libidn2~librtmp~libssh~libssh2+nghttp2 build_system=autotools libs=shared,static tls=openssl arch=linux-ubuntu22.04-skylake_avx512
 -                   ^nghttp2@1.57.0%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -               ^ncurses@6.4%gcc@11.4.0~symlinks+termlib abi=none build_system=autotools patches=7a351bc arch=linux-ubuntu22.04-skylake_avx512
 -           ^lz4@1.9.4%gcc@11.4.0+pic build_system=makefile libs=shared,static arch=linux-ubuntu22.04-skylake_avx512
 -           ^snappy@1.1.10%gcc@11.4.0~ipo+pic+shared build_system=cmake build_type=Release generator=make arch=linux-ubuntu22.04-skylake_avx512
 -       ^gcc-runtime@11.4.0%gcc@11.4.0 build_system=generic arch=linux-ubuntu22.04-skylake_avx512
 -       ^gmake@4.4.1%gcc@11.4.0~guile build_system=generic arch=linux-ubuntu22.04-skylake_avx512
 -       ^hdf5@1.14.3%gcc@11.4.0~cxx~fortran+hl~ipo~java~map+mpi+shared~subfiling~szip~threadsafe+tools api=default build_system=cmake build_type=Release generator=make patches=82088c8 arch=linux-ubuntu22.04-skylake_avx512
 -           ^pkgconf@1.9.5%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -       ^libaec@1.0.6%gcc@11.4.0~ipo+shared build_system=cmake build_type=Release generator=make arch=linux-ubuntu22.04-skylake_avx512
 -       ^openmpi@5.0.3%gcc@11.4.0~atomics~cuda~gpfs~internal-hwloc~internal-libevent~internal-pmix~java~legacylaunchers~lustre~memchecker~openshmem~orterunprefix~romio+rsh~static+vt+wrapper-rpath build_system=autotools fabrics=none romio-filesystem=none schedulers=none arch=linux-ubuntu22.04-skylake_avx512
 -           ^autoconf@2.72%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -               ^m4@1.4.19%gcc@11.4.0+sigsegv build_system=autotools patches=9dc5fbd,bfdffa7 arch=linux-ubuntu22.04-skylake_avx512
 -                   ^libsigsegv@2.14%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -           ^automake@1.16.5%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -           ^hwloc@2.9.1%gcc@11.4.0~cairo~cuda~gl~libudev+libxml2~netloc~nvml~oneapi-level-zero~opencl+pci~rocm build_system=autotools libs=shared,static arch=linux-ubuntu22.04-skylake_avx512
 -               ^libpciaccess@0.17%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -                   ^util-macros@1.19.3%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -               ^libxml2@2.10.3%gcc@11.4.0+pic~python+shared build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -                   ^xz@5.4.6%gcc@11.4.0~pic build_system=autotools libs=shared,static arch=linux-ubuntu22.04-skylake_avx512
 -           ^libevent@2.1.12%gcc@11.4.0+openssl build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -               ^openssl@3.2.1%gcc@11.4.0~docs+shared build_system=generic certs=mozilla arch=linux-ubuntu22.04-skylake_avx512
 -                   ^ca-certificates-mozilla@2023-05-30%gcc@11.4.0 build_system=generic arch=linux-ubuntu22.04-skylake_avx512
 -           ^libtool@2.4.7%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -               ^findutils@4.9.0%gcc@11.4.0 build_system=autotools patches=440b954 arch=linux-ubuntu22.04-skylake_avx512
 -           ^numactl@2.0.14%gcc@11.4.0 build_system=autotools patches=4e1d78c,62fc8a8,ff37630 arch=linux-ubuntu22.04-skylake_avx512
 -           ^openssh@9.7p1%gcc@11.4.0+gssapi build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -               ^krb5@1.20.1%gcc@11.4.0+shared build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -                   ^bison@3.8.2%gcc@11.4.0~color build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -                   ^gettext@0.22.4%gcc@11.4.0+bzip2+curses+git~libunistring+libxml2+pic+shared+tar+xz build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -                       ^tar@1.34%gcc@11.4.0 build_system=autotools zip=pigz arch=linux-ubuntu22.04-skylake_avx512
 -                           ^pigz@2.8%gcc@11.4.0 build_system=makefile arch=linux-ubuntu22.04-skylake_avx512
 -               ^libedit@3.1-20230828%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -               ^libxcrypt@4.4.35%gcc@11.4.0~obsolete_api build_system=autotools patches=4885da3 arch=linux-ubuntu22.04-skylake_avx512
 -           ^perl@5.38.0%gcc@11.4.0+cpanm+opcode+open+shared+threads build_system=generic patches=714e4d1 arch=linux-ubuntu22.04-skylake_avx512
 -               ^berkeley-db@18.1.40%gcc@11.4.0+cxx~docs+stl build_system=autotools patches=26090f4,b231fcc arch=linux-ubuntu22.04-skylake_avx512
 -               ^gdbm@1.23%gcc@11.4.0 build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -                   ^readline@8.2%gcc@11.4.0 build_system=autotools patches=bbf97f1 arch=linux-ubuntu22.04-skylake_avx512
 -           ^pmix@5.0.1%gcc@11.4.0~docs+pmi_backwards_compatibility~python~restful build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -       ^zlib-ng@2.1.6%gcc@11.4.0+compat+new_strategies+opt+pic+shared build_system=autotools arch=linux-ubuntu22.04-skylake_avx512
 -       ^zstd@1.5.6%gcc@11.4.0+programs build_system=makefile compression=none libs=shared,static arch=linux-ubuntu22.04-skylake_avx512

In theory, Spack doesn’t need any additional installation; just download and run! But in real life, additional steps are usually required before Spack can work in a practical sense. Read on…

Clean Environment

Many packages’ installs can be broken by changing environment variables. For example, a package might pick up the wrong build-time dependencies (most of them not specified) depending on the setting of PATH. GCC seems to be particularly vulnerable to these issues.

Therefore, it is recommended that Spack users run with a clean environment, especially for PATH. Only software that comes with the system, or that you know you wish to use with Spack, should be included. This procedure will avoid many strange build errors.

Optional: Alternate Prefix

You may want to run Spack out of a prefix other than the git repository you cloned. The spack clone command provides this functionality. To install spack in a new directory, simply type:

$ spack clone /my/favorite/prefix

This will install a new spack script in /my/favorite/prefix/bin, which you can use just like you would the regular spack script. Each copy of spack installs packages into its own $PREFIX/opt directory.

Compiler configuration

Spack has the ability to build packages with multiple compilers and compiler versions. Compilers can be made available to Spack by specifying them manually in compilers.yaml or packages.yaml, or automatically by running spack compiler find, but for convenience Spack will automatically detect compilers the first time it needs them.

spack compilers

You can see which compilers are available to Spack by running spack compilers or spack compiler list:

$ spack compilers
==> Available compilers
-- gcc ---------------------------------------------------------
    gcc@4.9.0  gcc@4.8.0  gcc@4.7.0  gcc@4.6.2  gcc@4.4.7
    gcc@4.8.2  gcc@4.7.1  gcc@4.6.3  gcc@4.6.1  gcc@4.1.2
-- intel -------------------------------------------------------
    intel@15.0.0  intel@14.0.0  intel@13.0.0  intel@12.1.0  intel@10.0
    intel@14.0.3  intel@13.1.1  intel@12.1.5  intel@12.0.4  intel@9.1
    intel@14.0.2  intel@13.1.0  intel@12.1.3  intel@11.1
    intel@14.0.1  intel@13.0.1  intel@12.1.2  intel@10.1
-- clang -------------------------------------------------------
    clang@3.4  clang@3.3  clang@3.2  clang@3.1
-- pgi ---------------------------------------------------------
    pgi@14.3-0   pgi@13.2-0  pgi@12.1-0   pgi@10.9-0  pgi@8.0-1
    pgi@13.10-0  pgi@13.1-1  pgi@11.10-0  pgi@10.2-0  pgi@7.1-3
    pgi@13.6-0   pgi@12.8-0  pgi@11.1-0   pgi@9.0-4   pgi@7.0-6

Any of these compilers can be used to build Spack packages. More on how this is done is in Specs & dependencies.

spack compiler add

An alias for spack compiler find.

spack compiler find

Lists the compilers currently available to Spack. If you do not see a compiler in this list, but you want to use it with Spack, you can simply run spack compiler find with the path to where the compiler is installed. For example:

$ spack compiler find /usr/local/tools/ic-13.0.079
==> Added 1 new compiler to ~/.spack/linux/compilers.yaml

Or you can run spack compiler find with no arguments to force auto-detection. This is useful if you do not know where compilers are installed, but you know that new compilers have been added to your PATH. For example, you might load a module, like this:

$ module load gcc/4.9.0
$ spack compiler find
==> Added 1 new compiler to ~/.spack/linux/compilers.yaml

This loads the environment module for gcc-4.9.0 to add it to PATH, and then it adds the compiler to Spack.


By default, spack does not fill in the modules: field in the compilers.yaml file. If you are using a compiler from a module, then you should add this field manually. See the section on Compilers Requiring Modules.

spack compiler info

If you want to see specifics on a particular compiler, you can run spack compiler info on it:

$ spack compiler info intel@15
    cc  = /usr/local/bin/icc-15.0.090
    cxx = /usr/local/bin/icpc-15.0.090
    f77 = /usr/local/bin/ifort-15.0.090
    fc  = /usr/local/bin/ifort-15.0.090
  modules = []
  operating_system = centos6

This shows which C, C++, and Fortran compilers were detected by Spack. Notice also that we didn’t have to be too specific about the version. We just said intel@15, and information about the only matching Intel compiler was displayed.

Manual compiler configuration

If auto-detection fails, you can manually configure a compiler by editing your ~/.spack/<platform>/compilers.yaml file. You can do this by running spack config edit compilers, which will open the file in your favorite editor.

Each compiler configuration in the file looks like this:

- compiler:
    modules: []
    operating_system: centos6
      cc: /usr/local/bin/icc-15.0.024-beta
      cxx: /usr/local/bin/icpc-15.0.024-beta
      f77: /usr/local/bin/ifort-15.0.024-beta
      fc: /usr/local/bin/ifort-15.0.024-beta
    spec: intel@15.0.0

For compilers that do not support Fortran (like clang), put None for f77 and fc:

- compiler:
    modules: []
    operating_system: centos6
      cc: /usr/bin/clang
      cxx: /usr/bin/clang++
      f77: None
      fc: None
    spec: clang@3.3svn

Once you save the file, the configured compilers will show up in the list displayed by spack compilers.

You can also add compiler flags to manually configured compilers. These flags should be specified in the flags section of the compiler specification. The valid flags are cflags, cxxflags, fflags, cppflags, ldflags, and ldlibs. For example:

- compiler:
    modules: []
    operating_system: centos6
      cc: /usr/bin/gcc
      cxx: /usr/bin/g++
      f77: /usr/bin/gfortran
      fc: /usr/bin/gfortran
      cflags: -O3 -fPIC
      cxxflags: -O3 -fPIC
      cppflags: -O3 -fPIC
    spec: gcc@4.7.2

These flags will be treated by spack as if they were entered from the command line each time this compiler is used. The compiler wrappers then inject those flags into the compiler command. Compiler flags entered from the command line will be discussed in more detail in the following section.

Some compilers also require additional environment configuration. Examples include Intels oneAPI and AMDs AOCC compiler suites, which have custom scripts for loading environment variables and setting paths. These variables should be specified in the environment section of the compiler specification. The operations available to modify the environment are set, unset, prepend_path, append_path, and remove_path. For example:

- compiler:
    modules: []
    operating_system: centos6
      cc: /opt/intel/oneapi/compiler/latest/linux/bin/icx
      cxx: /opt/intel/oneapi/compiler/latest/linux/bin/icpx
      f77: /opt/intel/oneapi/compiler/latest/linux/bin/ifx
      fc: /opt/intel/oneapi/compiler/latest/linux/bin/ifx
    spec: oneapi@latest
        MKL_ROOT: "/path/to/mkl/root"
      unset: # A list of environment variables to unset
        - CC
      prepend_path: # Similar for append|remove_path
        LD_LIBRARY_PATH: /ld/paths/added/by/setvars/sh


Spack is in the process of moving compilers from a separate attribute to be handled like all other packages. As part of this process, the compilers.yaml section will eventually be replaced by configuration in the packages.yaml section. This new configuration is now available, although it is not yet the default behavior.

Compilers can also be configured as external packages in the packages.yaml config file. Any external package for a compiler (e.g. gcc or llvm) will be treated as a configured compiler assuming the paths to the compiler executables are determinable from the prefix.

If the paths to the compiler executable are not determinable from the prefix, you can add them to the extra_attributes field. Similarly, all other fields from the compilers config can be added to the extra_attributes field for an external representing a compiler.

    - spec: gcc@12.2.0 arch=linux-rhel8-skylake
      prefix: /usr
            GCC_ROOT: /usr
    - spec: llvm+clang@15.0.0 arch=linux-rhel8-skylake
      prefix: /usr
          cc: /usr/bin/clang-with-suffix
          cxx: /usr/bin/clang++-with-extra-info
          fc: /usr/bin/gfortran
          f77: /usr/bin/gfortran
        - /usr/lib/llvm/

Build Your Own Compiler

If you are particular about which compiler/version you use, you might wish to have Spack build it for you. For example:

$ spack install gcc@4.9.3

Once that has finished, you will need to add it to your compilers.yaml file. You can then set Spack to use it by default by adding the following to your packages.yaml file:

    compiler: [gcc@4.9.3]

Compilers Requiring Modules

Many installed compilers will work regardless of the environment they are called with. However, some installed compilers require $LD_LIBRARY_PATH or other environment variables to be set in order to run; this is typical for Intel and other proprietary compilers.

In such a case, you should tell Spack which module(s) to load in order to run the chosen compiler (If the compiler does not come with a module file, you might consider making one by hand). Spack will load this module into the environment ONLY when the compiler is run, and NOT in general for a package’s install() method. See, for example, this compilers.yaml file:

- compiler:
    modules: [other/comp/gcc-5.3-sp3]
    operating_system: SuSE11
      cc: /usr/local/other/SLES11.3/gcc/5.3.0/bin/gcc
      cxx: /usr/local/other/SLES11.3/gcc/5.3.0/bin/g++
      f77: /usr/local/other/SLES11.3/gcc/5.3.0/bin/gfortran
      fc: /usr/local/other/SLES11.3/gcc/5.3.0/bin/gfortran
    spec: gcc@5.3.0

Some compilers require special environment settings to be loaded not just to run, but also to execute the code they build, breaking packages that need to execute code they just compiled. If it’s not possible or practical to use a better compiler, you’ll need to ensure that environment settings are preserved for compilers like this (i.e., you’ll need to load the module or source the compiler’s shell script).

By default, Spack tries to ensure that builds are reproducible by cleaning the environment before building. If this interferes with your compiler settings, you CAN use spack install --dirty as a workaround. Note that this MAY interfere with package builds.

Licensed Compilers

Some proprietary compilers require licensing to use. If you need to use a licensed compiler (eg, PGI), the process is similar to a mix of build your own, plus modules:

  1. Create a Spack package (if it doesn’t exist already) to install your compiler. Follow instructions on installing Licensed software.

  2. Once the compiler is installed, you should be able to test it by using Spack to load the module it just created, and running simple builds (eg: cc helloWorld.c && ./a.out)

  3. Add the newly-installed compiler to compilers.yaml as shown above.

Mixed Toolchains

Modern compilers typically come with related compilers for C, C++ and Fortran bundled together. When possible, results are best if the same compiler is used for all languages.

In some cases, this is not possible. For example, starting with macOS El Capitan (10.11), many packages no longer build with GCC, but XCode provides no Fortran compilers. The user is therefore forced to use a mixed toolchain: XCode-provided Clang for C/C++ and GNU gfortran for Fortran.

  1. You need to make sure that Xcode is installed. Run the following command:

    $ xcode-select --install

    If the Xcode command-line tools are already installed, you will see an error message:

    xcode-select: error: command line tools are already installed, use "Software Update" to install updates
  2. For most packages, the Xcode command-line tools are sufficient. However, some packages like qt require the full Xcode suite. You can check to see which you have installed by running:

    $ xcode-select -p

    If the output is:


    you already have the full Xcode suite installed. If the output is:


    you only have the command-line tools installed. The full Xcode suite can be installed through the App Store. Make sure you launch the Xcode application and accept the license agreement before using Spack. It may ask you to install additional components. Alternatively, the license can be accepted through the command line:

    $ sudo xcodebuild -license accept

    Note: the flag is -license, not --license.

  3. Run spack compiler find to locate Clang.

  4. There are different ways to get gfortran on macOS. For example, you can install GCC with Spack (spack install gcc), with Homebrew (brew install gcc), or from a DMG installer.

  5. The only thing left to do is to edit ~/.spack/darwin/compilers.yaml to provide the path to gfortran:

    - compiler:
      # ...
        cc: /usr/bin/clang
        cxx: /usr/bin/clang++
        f77: /path/to/bin/gfortran
        fc: /path/to/bin/gfortran
      spec: apple-clang@11.0.0

    If you used Spack to install GCC, you can get the installation prefix by spack location -i gcc (this will only work if you have a single version of GCC installed). Whereas for Homebrew, GCC is installed in /usr/local/Cellar/gcc/x.y.z. With the DMG installer, the correct path will be /usr/local/gfortran.

Compiler Verification

You can verify that your compilers are configured properly by installing a simple package. For example:

$ spack install zlib%gcc@5.3.0

Vendor-Specific Compiler Configuration

With Spack, things usually “just work” with GCC. Not so for other compilers. This section provides details on how to get specific compilers working.

Intel Compilers

Intel compilers are unusual because a single Intel compiler version can emulate multiple GCC versions. In order to provide this functionality, the Intel compiler needs GCC to be installed. Therefore, the following steps are necessary to successfully use Intel compilers:

  1. Install a version of GCC that implements the desired language features (spack install gcc).

  2. Tell the Intel compiler how to find that desired GCC. This may be done in one of two ways:

    “By default, the compiler determines which version of gcc or g++ you have installed from the PATH environment variable.

    If you want use a version of gcc or g++ other than the default version on your system, you need to use either the -gcc-name or -gxx-name compiler option to specify the path to the version of gcc or g++ that you want to use.”

    Intel Reference Guide

Intel compilers may therefore be configured in one of two ways with Spack: using modules, or using compiler flags.

Configuration with Modules

One can control which GCC is seen by the Intel compiler with modules. A module must be loaded both for the Intel Compiler (so it will run) and GCC (so the compiler can find the intended GCC). The following configuration in compilers.yaml illustrates this technique:

- compiler:
    modules: [gcc-4.9.3, intel-15.0.24]
    operating_system: centos7
      cc: /opt/intel-15.0.24/bin/icc-15.0.24-beta
      cxx: /opt/intel-15.0.24/bin/icpc-15.0.24-beta
      f77: /opt/intel-15.0.24/bin/ifort-15.0.24-beta
      fc: /opt/intel-15.0.24/bin/ifort-15.0.24-beta
    spec: intel@


The version number on the Intel compiler is a combination of the “native” Intel version number and the GNU compiler it is targeting.

Command Line Configuration

One can also control which GCC is seen by the Intel compiler by adding flags to the icc command:

  1. Identify the location of the compiler you just installed:

    $ spack location --install-dir gcc
  2. Set up compilers.yaml, for example:

    - compiler:
        modules: [intel-15.0.24]
        operating_system: centos7
          cc: /opt/intel-15.0.24/bin/icc-15.0.24-beta
          cxx: /opt/intel-15.0.24/bin/icpc-15.0.24-beta
          f77: /opt/intel-15.0.24/bin/ifort-15.0.24-beta
          fc: /opt/intel-15.0.24/bin/ifort-15.0.24-beta
          cflags: -gcc-name ~/spack/opt/spack/linux-centos7-x86_64/gcc-4.9.3-iy4rw.../bin/gcc
          cxxflags: -gxx-name ~/spack/opt/spack/linux-centos7-x86_64/gcc-4.9.3-iy4rw.../bin/g++
          fflags: -gcc-name ~/spack/opt/spack/linux-centos7-x86_64/gcc-4.9.3-iy4rw.../bin/gcc
        spec: intel@


PGI comes with two sets of compilers for C++ and Fortran, distinguishable by their names. “Old” compilers:

cc:  /soft/pgi/15.10/linux86-64/15.10/bin/pgcc
cxx: /soft/pgi/15.10/linux86-64/15.10/bin/pgCC
f77: /soft/pgi/15.10/linux86-64/15.10/bin/pgf77
fc:  /soft/pgi/15.10/linux86-64/15.10/bin/pgf90

“New” compilers:

cc:  /soft/pgi/15.10/linux86-64/15.10/bin/pgcc
cxx: /soft/pgi/15.10/linux86-64/15.10/bin/pgc++
f77: /soft/pgi/15.10/linux86-64/15.10/bin/pgfortran
fc:  /soft/pgi/15.10/linux86-64/15.10/bin/pgfortran

Older installations of PGI contains just the old compilers; whereas newer installations contain the old and the new. The new compiler is considered preferable, as some packages (hdf) will not build with the old compiler.

When auto-detecting a PGI compiler, there are cases where Spack will find the old compilers, when you really want it to find the new compilers. It is best to check this compilers.yaml; and if the old compilers are being used, change pgf77 and pgf90 to pgfortran.

Other issues:

  • There are reports that some packages will not build with PGI, including libpciaccess and openssl. A workaround is to build these packages with another compiler and then use them as dependencies for PGI-build packages. For example:

    $ spack install openmpi%pgi ^libpciaccess%gcc
  • PGI requires a license to use; see Licensed Compilers for more information on installation.


It is believed the problem with HDF 4 is that everything is compiled with the F77 compiler, but at some point some Fortran 90 code slipped in there. So compilers that can handle both FORTRAN 77 and Fortran 90 (gfortran, pgfortran, etc) are fine. But compilers specific to one or the other (pgf77, pgf90) won’t work.


The Numerical Algorithms Group provides a licensed Fortran compiler. Like Clang, this requires you to set up a Mixed Toolchains. It is recommended to use GCC for your C/C++ compilers.

The NAG Fortran compilers are a bit more strict than other compilers, and many packages will fail to install with error messages like:

Error: mpi_comm_spawn_multiple_f90.f90: Argument 3 to MPI_COMM_SPAWN_MULTIPLE has data type DOUBLE PRECISION in reference from MPI_COMM_SPAWN_MULTIPLEN and CHARACTER in reference from MPI_COMM_SPAWN_MULTIPLEA

In order to convince the NAG compiler not to be too picky about calling conventions, you can use FFLAGS=-mismatch and FCFLAGS=-mismatch. This can be done through the command line:

$ spack install openmpi fflags="-mismatch"

Or it can be set permanently in your compilers.yaml:

- compiler:
 modules: []
 operating_system: centos6
   cc: /soft/spack/opt/spack/linux-x86_64/gcc-5.3.0/gcc-6.1.0-q2zosj3igepi3pjnqt74bwazmptr5gpj/bin/gcc
   cxx: /soft/spack/opt/spack/linux-x86_64/gcc-5.3.0/gcc-6.1.0-q2zosj3igepi3pjnqt74bwazmptr5gpj/bin/g++
   f77: /soft/spack/opt/spack/linux-x86_64/gcc-4.4.7/nag-6.1-jt3h5hwt5myezgqguhfsan52zcskqene/bin/nagfor
   fc: /soft/spack/opt/spack/linux-x86_64/gcc-4.4.7/nag-6.1-jt3h5hwt5myezgqguhfsan52zcskqene/bin/nagfor
   fflags: -mismatch
 spec: nag@6.1

System Packages

Once compilers are configured, one needs to determine which pre-installed system packages, if any, to use in builds. This is configured in the file ~/.spack/packages.yaml. For example, to use an OpenMPI installed in /opt/local, one would use:

        - spec: openmpi@1.10.1
          prefix: /opt/local
        buildable: False

In general, Spack is easier to use and more reliable if it builds all of its own dependencies. However, there are several packages for which one commonly needs to use system versions:


On supercomputers, sysadmins have already built MPI versions that take into account the specifics of that computer’s hardware. Unless you know how they were built and can choose the correct Spack variants, you are unlikely to get a working MPI from Spack. Instead, use an appropriate pre-installed MPI.

If you choose a pre-installed MPI, you should consider using the pre-installed compiler used to build that MPI; see above on compilers.yaml.


The openssl package underlies much of modern security in a modern OS; an attacker can easily “pwn” any computer on which they can modify SSL. Therefore, any openssl used on a system should be created in a “trusted environment” — for example, that of the OS vendor.

OpenSSL is also updated by the OS vendor from time to time, in response to security problems discovered in the wider community. It is in everyone’s best interest to use any newly updated versions as soon as they come out. Modern Linux installations have standard procedures for security updates without user involvement.

Spack running at user-level is not a trusted environment, nor do Spack users generally keep up-to-date on the latest security holes in SSL. For these reasons, a Spack-installed OpenSSL should likely not be trusted.

As long as the system-provided SSL works, you can use it instead. One can check if it works by trying to download an https://. For example:

$ curl -O

To tell Spack to use the system-supplied OpenSSL, first determine what version you have:

$ openssl version
OpenSSL 1.0.2g  1 Mar 2016

Then add the following to ~/.spack/packages.yaml:

        - spec: openssl@1.0.2g
          prefix: /usr
        buildable: False


The recommended way to use system-supplied BLAS / LAPACK packages is to add the following to packages.yaml:

        - spec: netlib-lapack@3.6.1
          prefix: /usr
        buildable: False
            blas: [netlib-lapack]
            lapack: [netlib-lapack]


Above we pretend that the system-provided BLAS / LAPACK is netlib-lapack only because it is the only BLAS / LAPACK provider which use standard names for libraries (as opposed to, for example,

Although we specify external package in /usr, Spack is smart enough not to add /usr/lib to RPATHs, where it could cause unrelated system libraries to be used instead of their Spack equivalents. usr/bin will be present in PATH, however it will have lower precedence compared to paths from other dependencies. This ensures that binaries in Spack dependencies are preferred over system binaries.


Some Spack packages use git to download, which might not work on some computers. For example, the following error was encountered on a Macintosh during spack install julia@master:

==> Cloning git repository:
  on branch master
Cloning into 'julia'...
fatal: unable to access '':
    SSL certificate problem: unable to get local issuer certificate

This problem is related to OpenSSL, and in some cases might be solved by installing a new version of git and openssl:

  1. Run spack install git

  2. Add the output of spack module tcl loads git to your .bashrc.

If this doesn’t work, it is also possible to disable checking of SSL certificates by using:

$ spack --insecure install

Using --insecure makes Spack disable SSL checking when fetching from websites and from git.


This workaround should be used ONLY as a last resort! Without SSL certificate verification, spack and git will download from sites you wouldn’t normally trust. The code you download and run may then be compromised! While this is not a major issue for archives that will be checksummed, it is especially problematic when downloading from name Git branches or tags, which relies entirely on trusting a certificate for security (no verification).

certificate for security (no verification).

Utilities Configuration

Although Spack does not need installation per se, it does rely on other packages to be available on its host system. If those packages are out of date or missing, then Spack will not work. Sometimes, an appeal to the system’s package manager can fix such problems. If not, the solution is have Spack install the required packages, and then have Spack use them.

For example, if curl doesn’t work, one could use the following steps to provide Spack a working curl:

$ spack install curl
$ spack load curl

or alternately:

$ spack module tcl loads curl >>~/.bashrc

or if environment modules don’t work:

$ export PATH=`spack location --install-dir curl`/bin:$PATH

External commands are used by Spack in two places: within core Spack, and in the package recipes. The bootstrapping procedure for these two cases is somewhat different, and is treated separately below.

Core Spack Utilities

Core Spack uses the following packages, mainly to download and unpack source code: curl, env, git, go, hg, svn, tar, unzip, patch

As long as the user’s environment is set up to successfully run these programs from outside of Spack, they should work inside of Spack as well. They can generally be activated as in the curl example above; or some systems might already have an appropriate hand-built environment module that may be loaded. Either way works.

A few notes on specific programs in this list:

cURL, git, Mercurial, etc.

Spack depends on cURL to download tarballs, the format that most Spack-installed packages come in. Your system’s cURL should always be able to download unencrypted http://. However, the cURL on some systems has problems with SSL-enabled https:// URLs, due to outdated / insecure versions of OpenSSL on those systems. This will prevent Spack from installing any software requiring https:// until a new cURL has been installed, using the technique above.


remember that if you install curl via Spack that it may rely on a user-space OpenSSL that is not upgraded regularly. It may fall out of date faster than your system OpenSSL.

Some packages use source code control systems as their download method: git, hg, svn and occasionally go. If you had to install a new curl, then chances are the system-supplied version of these other programs will also not work, because they also rely on OpenSSL. Once curl has been installed, you can similarly install the others.

Package Utilities

Spack may also encounter bootstrapping problems inside a package’s install() method. In this case, Spack will normally be running inside a sanitized build environment. This includes all of the package’s dependencies, but none of the environment Spack inherited from the user: if you load a module or modify $PATH before launching Spack, it will have no effect.

In this case, you will likely need to use the --dirty flag when running spack install, causing Spack to not sanitize the build environment. You are now responsible for making sure that environment does not do strange things to Spack or its installs.

Another way to get Spack to use its own version of something is to add that something to a package that needs it. For example:

depends_on('binutils', type='build')

This is considered best practice for some common build dependencies, such as autotools (if the autoreconf command is needed) and cmakecmake especially, because different packages require a different version of CMake.


Sometimes, strange error messages can happen while building a package. For example, ld might crash. Or one receives a message like:

ld: final link failed: Nonrepresentable section on output


ld: .../_fftpackmodule.o: unrecognized relocation (0x2a) in section `.text'

These problems are often caused by an outdated binutils on your system. Unlike CMake or Autotools, adding depends_on('binutils') to every package is not considered a best practice because every package written in C/C++/Fortran would need it. A potential workaround is to load a recent binutils into your environment and use the --dirty flag.

GPG Signing

spack gpg

Spack has support for signing and verifying packages using GPG keys. A separate keyring is used for Spack, so any keys available in the user’s home directory are not used.

spack gpg init

When Spack is first installed, its keyring is empty. Keys stored in var/spack/gpg are the default keys for a Spack installation. These keys may be imported by running spack gpg init. This will import the default keys into the keyring as trusted keys.

Trusting keys

Additional keys may be added to the keyring using spack gpg trust <keyfile>. Once a key is trusted, packages signed by the owner of they key may be installed.

Creating keys

You may also create your own key so that you may sign your own packages using spack gpg create <name> <email>. By default, the key has no expiration, but it may be set with the --expires <date> flag (see the gnupg2 documentation for accepted date formats). It is also recommended to add a comment as to the use of the key using the --comment <comment> flag. The public half of the key can also be exported for sharing with others so that they may use packages you have signed using the --export <keyfile> flag. Secret keys may also be later exported using the spack gpg export <location> [<key>...] command.


Key creation speed

The creation of a new GPG key requires generating a lot of random numbers. Depending on the entropy produced on your system, the entire process may take a long time (even appearing to hang). Virtual machines and cloud instances are particularly likely to display this behavior.

To speed it up you may install tools like rngd, which is usually available as a package in the host OS. On e.g. an Ubuntu machine you need to give the following commands:

$ sudo apt-get install rng-tools
$ sudo rngd -r /dev/urandom

before generating the keys.

Another alternative is haveged, which can be installed on RHEL/CentOS machines as follows:

$ sudo yum install haveged
$ sudo chkconfig haveged on

This Digital Ocean tutorial provides a good overview of sources of randomness.

Here is an example of creating a key. Note that we provide a name for the key first (which we can use to reference the key later) and an email address:

$ spack gpg create dinosaur

If you want to export the key as you create it:

$ spack gpg create --export dinosaur

Or the private key:

$ spack gpg create --export-secret key.priv dinosaur

You can include both --export and --export-secret, each with an output file of choice, to export both.

Listing keys

In order to list the keys available in the keyring, the spack gpg list command will list trusted keys with the --trusted flag and keys available for signing using --signing. If you would like to remove keys from your keyring, spack gpg untrust <keyid>. Key IDs can be email addresses, names, or (best) fingerprints. Here is an example of listing the key that we just created:

gpgconf: socketdir is '/run/user/1000/gnupg'
pub   rsa4096 2021-03-25 [SC]
uid           [ultimate] dinosaur (GPG created for Spack) <>

Note that the name “dinosaur” can be seen under the uid, which is the unique id. We might need this reference if we want to export or otherwise reference the key.

Signing and Verifying Packages

In order to sign a package, spack gpg sign <file> should be used. By default, the signature will be written to <file>.asc, but that may be changed by using the --output <file> flag. If there is only one signing key available, it will be used, but if there is more than one, the key to use must be specified using the --key <keyid> flag. The --clearsign flag may also be used to create a signed file which contains the contents, but it is not recommended. Signed packages may be verified by using spack gpg verify <file>.

Exporting Keys

You likely might want to export a public key, and that looks like this. Let’s use the previous example and ask spack to export the key with uid “dinosaur.” We will provide an output location (typically a *.pub file) and the name of the key.

$ spack gpg export dinosaur

You can then look at the created file,, to see the exported key. If you want to include the private key, then just add –secret:

$ spack gpg export --secret dinosaur.priv dinosaur

This will write the private key to the file dinosaur.priv.


You should be very careful about exporting private keys. You likely would only want to do this in the context of moving your spack installation to a different server, and wanting to preserve keys for a buildcache. If you are unsure about exporting, you can ask your local system administrator or for help on an issue or the Spack slack.

Spack on Cray

Spack differs slightly when used on a Cray system. The architecture spec can differentiate between the front-end and back-end processor and operating system. For example, on Edison at NERSC, the back-end target processor is “Ivy Bridge”, so you can specify to use the back-end this way:

$ spack install zlib target=ivybridge

You can also use the operating system to build against the back-end:

$ spack install zlib os=CNL10

Notice that the name includes both the operating system name and the major version number concatenated together.

Alternatively, if you want to build something for the front-end, you can specify the front-end target processor. The processor for a login node on Edison is “Sandy bridge” so we specify on the command line like so:

$ spack install zlib target=sandybridge

And the front-end operating system is:

$ spack install zlib os=SuSE11

Cray compiler detection

Spack can detect compilers using two methods. For the front-end, we treat everything the same. The difference lies in back-end compiler detection. Back-end compiler detection is made via the Tcl module avail command. Once it detects the compiler it writes the appropriate PrgEnv and compiler module name to compilers.yaml and sets the paths to each compiler with Cray's compiler wrapper names (i.e. cc, CC, ftn). During build time, Spack will load the correct PrgEnv and compiler module and will call appropriate wrapper.

The compilers.yaml config file will also differ. There is a modules section that is filled with the compiler’s Programming Environment and module name. On other systems, this field is empty []:

- compiler:
      - PrgEnv-intel
      - intel/15.0.109

As mentioned earlier, the compiler paths will look different on a Cray system. Since most compilers are invoked using cc, CC and ftn, the paths for each compiler are replaced with their respective Cray compiler wrapper names:

  cc: cc
  cxx: CC
  f77: ftn
  fc: ftn

As opposed to an explicit path to the compiler executable. This allows Spack to call the Cray compiler wrappers during build time.

For more on compiler configuration, check out Compiler configuration.

Spack sets the default Cray link type to dynamic, to better match other other platforms. Individual packages can enable static linking (which is the default outside of Spack on cray systems) using the -static flag.

Setting defaults and using Cray modules

If you want to use default compilers for each PrgEnv and also be able to load cray external modules, you will need to set up a packages.yaml.

Here’s an example of an external configuration for cray modules:

    - spec: "mpich@7.3.1%gcc@5.2.0 arch=cray_xc-haswell-CNL10"
      - cray-mpich
    - spec: "mpich@7.3.1%intel@ arch=cray_xc-haswell-CNL10"
      - cray-mpich
      mpi: [mpich]

This tells Spack that for whatever package that depends on mpi, load the cray-mpich module into the environment. You can then be able to use whatever environment variables, libraries, etc, that are brought into the environment via module load.


For Cray-provided packages, it is best to use modules: instead of prefix: in packages.yaml, because the Cray Programming Environment heavily relies on modules (e.g., loading the cray-mpich module adds MPI libraries to the compiler wrapper link line).

You can set the default compiler that Spack can use for each compiler type. If you want to use the Cray defaults, then set them under all: in packages.yaml. In the compiler field, set the compiler specs in your order of preference. Whenever you build with that compiler type, Spack will concretize to that version.

Here is an example of a full packages.yaml used at NERSC

    - spec: "mpich@7.3.1%gcc@5.2.0 arch=cray_xc-CNL10-ivybridge"
      - cray-mpich
    - spec: "mpich@7.3.1%intel@ arch=cray_xc-SuSE11-ivybridge"
      - cray-mpich
    buildable: False
    - spec: "netcdf@ arch=cray_xc-CNL10-ivybridge"
      - cray-netcdf
    - spec: "netcdf@ arch=cray_xc-CNL10-ivybridge"
      - cray-netcdf
    buildable: False
    - spec: "hdf5@1.8.14%gcc@5.2.0 arch=cray_xc-CNL10-ivybridge"
      - cray-hdf5
    - spec: "hdf5@1.8.14%intel@ arch=cray_xc-CNL10-ivybridge"
      - cray-hdf5
    buildable: False
    compiler: [gcc@5.2.0, intel@]
      mpi: [mpich]

Here we tell spack that whenever we want to build with gcc use version 5.2.0 or if we want to build with intel compilers, use version We add a spec for each compiler type for each cray modules. This ensures that for each compiler on our system we can use that external module.

For more on external packages check out the section External Packages.

Using Linux containers on Cray machines

Spack uses environment variables particular to the Cray programming environment to determine which systems are Cray platforms. These environment variables may be propagated into containers that are not using the Cray programming environment.

To ensure that Spack does not autodetect the Cray programming environment, unset the environment variable MODULEPATH. This will cause Spack to treat a linux container on a Cray system as a base linux distro.

Spack On Windows

Windows support for Spack is currently under development. While this work is still in an early stage, it is currently possible to set up Spack and perform a few operations on Windows. This section will guide you through the steps needed to install Spack and start running it on a fresh Windows machine.

Step 1: Install prerequisites

To use Spack on Windows, you will need the following packages:

Required: * Microsoft Visual Studio * Python * Git

Optional: * Intel Fortran (needed for some packages)


Currently MSVC is the only compiler tested for C/C++ projects. Intel OneAPI provides Fortran support.

Microsoft Visual Studio

Microsoft Visual Studio provides the only Windows C/C++ compiler that is currently supported by Spack. Spack additionally requires that the Windows SDK (including WGL) to be installed as part of your visual studio installation as it is required to build many packages from source.

We require several specific components to be included in the Visual Studio installation. One is the C/C++ toolset, which can be selected as “Desktop development with C++” or “C++ build tools,” depending on installation type (Professional, Build Tools, etc.) The other required component is “C++ CMake tools for Windows,” which can be selected from among the optional packages. This provides CMake and Ninja for use during Spack configuration.

If you already have Visual Studio installed, you can make sure these components are installed by rerunning the installer. Next to your installation, select “Modify” and look at the “Installation details” pane on the right.

Intel Fortran

For Fortran-based packages on Windows, we strongly recommend Intel’s oneAPI Fortran compilers. The suite is free to download from Intel’s website, located at The executable of choice for Spack will be Intel’s Beta Compiler, ifx, which supports the classic compiler’s (ifort’s) frontend and runtime libraries by using LLVM.


As Spack is a Python-based package, an installation of Python will be needed to run it. Python 3 can be downloaded and installed from the Windows Store, and will be automatically added to your PATH in this case.


Spack currently supports Python versions later than 3.2 inclusive.


A bash console and GUI can be downloaded from If you are unfamiliar with Git, there are a myriad of resources online to help guide you through checking out repositories and switching development branches.

When given the option of adjusting your PATH, choose the Git from the command line and also from 3rd-party software option. This will automatically update your PATH variable to include the git command.

Spack support on Windows is currently dependent on installing the Git for Windows project as the project providing Git support on Windows. This is additionally the recommended method for installing Git on Windows, a link to which can be found above. Spack requires the utilities vendored by this project.

utilities vendored by this project.

Step 2: Install and setup Spack

We are now ready to get the Spack environment set up on our machine. We begin by using Git to clone the Spack repo, hosted at into a desired directory, for our purposes today, called spack_install.

In order to install Spack with Windows support, run the following one liner in a Windows CMD prompt.

git clone


If you chose to install Spack into a directory on Windows that is set up to require Administrative Privileges, Spack will require elevated privileges to run. Administrative Privileges can be denoted either by default such as C:\Program Files, or aministrator applied administrative restrictions on a directory that spack installs files to such as C:\Users

Step 3: Run and configure Spack

To use Spack, run bin\spack_cmd.bat (you may need to Run as Administrator) from the top-level spack directory. This will provide a Windows command prompt with an environment properly set up with Spack and its prerequisites. If you receive a warning message that Python is not in your PATH (which may happen if you installed Python from the website and not the Windows Store) add the location of the Python executable to your PATH now. You can permanently add Python to your PATH variable by using the Edit the system environment variables utility in Windows Control Panel.


Alternatively, Powershell can be used in place of CMD

To configure Spack, first run the following command inside the Spack console:

spack compiler find

This creates a .staging directory in our Spack prefix, along with a windows subdirectory containing a compilers.yaml file. On a fresh Windows install with the above packages installed, this command should only detect Microsoft Visual Studio and the Intel Fortran compiler will be integrated within the first version of MSVC present in the compilers.yaml output.

Spack provides a default config.yaml file for Windows that it will use unless overridden. This file is located at etc\spack\defaults\windows\config.yaml. You can read more on how to do this and write your own configuration files in the Configuration Files section of our documentation. If you do this, pay particular attention to the build_stage block of the file as this specifies the directory that will temporarily hold the source code for the packages to be installed. This path name must be sufficiently short for compliance with cmd, otherwise you will see build errors during installation (particularly with CMake) tied to long path names.

To allow Spack use of external tools and dependencies already on your system, the external pieces of software must be described in the packages.yaml file. There are two methods to populate this file:

The first and easiest choice is to use Spack to find installation on your system. In the Spack terminal, run the following commands:

spack external find cmake
spack external find ninja

The spack external find <name> will find executables on your system with the same name given. The command will store the items found in packages.yaml in the .staging\ directory.

Assuming that the command found CMake and Ninja executables in the previous step, continue to Step 4. If no executables were found, we may need to manually direct spack towards the CMake and Ninja installations we set up with Visual Studio. Therefore, your packages.yaml file will look something like this, with possibly slight variants in the paths to CMake and Ninja:

    - spec: cmake@3.19
      prefix: 'c:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\CMake\CMake'
    buildable: False
    - spec: ninja@1.8.2
      prefix: 'c:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\CMake\Ninja'
    buildable: False

You can also use an separate installation of CMake if you have one and prefer to use it. If you don’t have a path to Ninja analogous to the above, then you can obtain it by running the Visual Studio Installer and following the instructions at the start of this section. Also note that .yaml files use spaces for indentation and not tabs, so ensure that this is the case when editing one directly.


Cygwin The use of Cygwin is not officially supported by Spack and is not tested. However Spack will not throw an error, so use if choosing to use Spack with Cygwin, know that no functionality is garunteed.

Step 4: Use Spack

Once the configuration is complete, it is time to give the installation a test. Install a basic package though the Spack console via:

spack install cpuinfo

If in the previous step, you did not have CMake or Ninja installed, running the command above should bootstrap both packages

Windows Compatible Packages

Not all spack packages currently have Windows support. Some are inherently incompatible with the platform, and others simply have yet to be ported. To view the current set of packages with Windows support, the list command should be used via spack list -t windows. If there’s a package you’d like to install on Windows but is not in that list, feel free to reach out to request the port or contribute the port yourself.


This is by no means a comprehensive list, some packages may have ports that were not tagged while others may just work out of the box on Windows and have not been tagged as such.

For developers

The intent is to provide a Windows installer that will automatically set up Python, Git, and Spack, instead of requiring the user to do so manually. Instructions for creating the installer are at

Alternatively a pre-built copy of the Windows installer is available as an artifact of Spack’s Windows CI available at each run of the CI on develop or any PR.