Feature Overview

This is a high-level overview of features that make Spack different from other package managers and port systems.

Simple package installation

Installing the default version of a package is simple. This will install the latest version of the mpileaks package and all of its dependencies:

$ spack install mpileaks

Custom versions & configurations

Spack allows installation to be customized. Users can specify the version, build compiler, compile-time options, and cross-compile platform, all on the command line.

# Install a particular version by appending @
$ spack install mpileaks@1.1.2

# Specify a compiler (and its version), with %
$ spack install mpileaks@1.1.2 %gcc@4.7.3

# Add special compile-time options by name
$ spack install mpileaks@1.1.2 %gcc@4.7.3 debug=True

# Add special boolean compile-time options with +
$ spack install mpileaks@1.1.2 %gcc@4.7.3 +debug

# Add compiler flags using the conventional names
$ spack install mpileaks@1.1.2 %gcc@4.7.3 cppflags="-O3 -floop-block"

# Cross-compile for a different micro-architecture with target=
$ spack install mpileaks@1.1.2 target=icelake

Users can specify as many or few options as they care about. Spack will fill in the unspecified values with sensible defaults. The two listed syntaxes for variants are identical when the value is boolean.

Customize dependencies

Spack allows dependencies of a particular installation to be customized extensively. Suppose that hdf5 depends on openmpi and indirectly on hwloc. Using ^, users can add custom configurations for the dependencies:

# Install hdf5 and link it with specific versions of openmpi and hwloc
$ spack install hdf5@1.10.1 %gcc@4.7.3 +debug ^openmpi+cuda fabrics=auto ^hwloc+gl

Non-destructive installs

Spack installs every unique package/dependency configuration into its own prefix, so new installs will not break existing ones.

Packages can peacefully coexist

Spack avoids library misconfiguration by using RPATH to link dependencies. When a user links a library or runs a program, it is tied to the dependencies it was built with, so there is no need to manipulate LD_LIBRARY_PATH at runtime.

Creating packages is easy

To create a new packages, all Spack needs is a URL for the source archive. The spack create command will create a boilerplate package file, and the package authors can fill in specific build steps in pure Python.

For example, this command:

$ spack create https://ftp.osuosl.org/pub/blfs/conglomeration/libelf/libelf-0.8.13.tar.gz

creates a simple python file:

from spack.package import *

class Libelf(AutotoolsPackage):
    """FIXME: Put a proper description of your package here."""

    # FIXME: Add a proper url for your package's homepage here.
    homepage = "https://www.example.com"
    url = "https://ftp.osuosl.org/pub/blfs/conglomeration/libelf/libelf-0.8.13.tar.gz"

    # FIXME: Add a list of GitHub accounts to
    # notify when the package is updated.
    # maintainers("github_user1", "github_user2")

    version("0.8.13", sha256="591a9b4ec81c1f2042a97aa60564e0cb79d041c52faa7416acb38bc95bd2c76d")

    # FIXME: Add dependencies if required.
    # depends_on("foo")

    def configure_args(self):
        # FIXME: Add arguments other than --prefix
        # FIXME: If not needed delete this function
        args = []
        return args

It doesn’t take much python coding to get from there to a working package:

from spack.package import *

class Libelf(AutotoolsPackage):
    """libelf lets you read, modify or create ELF object files in an
    architecture-independent way. The library takes care of size
    and endian issues, e.g. you can process a file for SPARC
    processors on an Intel-based system. Note: libelf is no longer
    maintained and packages that depend on libelf should migrate to

    # The original homepage no longer exists, but the tar file is
    # archived at fossies.org.
    # homepage = "http://www.mr511.de/software/english.html"

    homepage = "https://directory.fsf.org/wiki/Libelf"

    urls = [


    version("0.8.13", sha256="591a9b4ec81c1f2042a97aa60564e0cb79d041c52faa7416acb38bc95bd2c76d")


    # configure: error: neither int nor long is 32-bit
    depends_on("automake", when="platform=darwin", type="build")
    depends_on("autoconf", when="platform=darwin", type="build")
    depends_on("libtool", when="platform=darwin", type="build")
    depends_on("m4", when="platform=darwin", type="build")

    def force_autoreconf(self):
        return self.spec.satisfies("platform=darwin")

    def configure_args(self):
        args = ["--enable-shared", "--disable-debug"]

        # config.sub: invalid option -apple-darwin21.6.0
        if self.spec.satisfies("platform=darwin target=aarch64:"):

        return args

    def install(self, spec, prefix):
        make("install", parallel=False)

    def flag_handler(self, name, flags):
        if name == "cflags":
            if self.spec.satisfies("%clang@16:"):
        return (flags, None, None)

Spack also provides wrapper functions around common commands like configure, make, and cmake to make writing packages simple.