169 lines
6.8 KiB
ReStructuredText
169 lines
6.8 KiB
ReStructuredText
.. _build-settings:
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======================================
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Build customization
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======================================
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Spack allows you to customize how your software is built through the
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``packages.yaml`` file. Using it, you can make Spack prefer particular
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implementations of virtual dependencies (e.g., compilers, MPI, or BLAS),
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or you can make it prefer to build with particular compilers. You can
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also tell Spack to use *external* installations of certain software.
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At a high level, the ``packages.yaml`` file is structured like this:
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.. code-block:: yaml
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packages:
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package1:
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# settings for package1
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package2:
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# settings for package2
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# ...
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all:
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# settings that apply to all packages.
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So you can either set build preferences *specifically* for one package,
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or you can specify that certain settings should apply to all packages.
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The types of settings you can customize are described in detail below.
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Spack's build defaults are in the default
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``etc/spack/defaults/packages.yaml`` file. You can override them in
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``~/.spack/packages.yaml`` or ``etc/spack/packages.yaml``. For more
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details on how this works, see :ref:`configuration-scopes`
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.. _sec-external-packages:
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-----------------
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External Packages
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-----------------
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Spack can be configured to use externally-installed
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packages rather than building its own packages. This may be desirable
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if machines ship with system packages, such as a customized MPI
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that should be used instead of Spack building its own MPI.
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External packages are configured through the ``packages.yaml`` file found
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in a Spack installation's ``etc/spack/`` or a user's ``~/.spack/``
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directory. Here's an example of an external configuration:
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.. code-block:: yaml
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packages:
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openmpi:
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paths:
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openmpi@1.4.3%gcc@4.4.7 arch=linux-x86_64-debian7: /opt/openmpi-1.4.3
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openmpi@1.4.3%gcc@4.4.7 arch=linux-x86_64-debian7+debug: /opt/openmpi-1.4.3-debug
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openmpi@1.6.5%intel@10.1 arch=linux-x86_64-debian7: /opt/openmpi-1.6.5-intel
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This example lists three installations of OpenMPI, one built with gcc,
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one built with gcc and debug information, and another built with Intel.
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If Spack is asked to build a package that uses one of these MPIs as a
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dependency, it will use the the pre-installed OpenMPI in
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the given directory. Packages.yaml can also be used to specify modules
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Each ``packages.yaml`` begins with a ``packages:`` token, followed
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by a list of package names. To specify externals, add a ``paths`` or ``modules``
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token under the package name, which lists externals in a
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``spec: /path`` or ``spec: module-name`` format. Each spec should be as
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well-defined as reasonably possible. If a
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package lacks a spec component, such as missing a compiler or
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package version, then Spack will guess the missing component based
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on its most-favored packages, and it may guess incorrectly.
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Each package version and compiler listed in an external should
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have entries in Spack's packages and compiler configuration, even
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though the package and compiler may not ever be built.
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The packages configuration can tell Spack to use an external location
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for certain package versions, but it does not restrict Spack to using
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external packages. In the above example, if an OpenMPI 1.8.4 became
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available Spack may choose to start building and linking with that version
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rather than continue using the pre-installed OpenMPI versions.
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To prevent this, the ``packages.yaml`` configuration also allows packages
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to be flagged as non-buildable. The previous example could be modified to
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be:
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.. code-block:: yaml
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packages:
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openmpi:
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paths:
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openmpi@1.4.3%gcc@4.4.7 arch=linux-x86_64-debian7: /opt/openmpi-1.4.3
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openmpi@1.4.3%gcc@4.4.7 arch=linux-x86_64-debian7+debug: /opt/openmpi-1.4.3-debug
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openmpi@1.6.5%intel@10.1 arch=linux-x86_64-debian7: /opt/openmpi-1.6.5-intel
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buildable: False
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The addition of the ``buildable`` flag tells Spack that it should never build
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its own version of OpenMPI, and it will instead always rely on a pre-built
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OpenMPI. Similar to ``paths``, ``buildable`` is specified as a property under
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a package name.
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If an external module is specified as not buildable, then Spack will load the
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external module into the build environment which can be used for linking.
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The ``buildable`` does not need to be paired with external packages.
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It could also be used alone to forbid packages that may be
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buggy or otherwise undesirable.
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.. _concretization-preferences:
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--------------------------
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Concretization Preferences
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--------------------------
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Spack can be configured to prefer certain compilers, package
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versions, depends_on, and variants during concretization.
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The preferred configuration can be controlled via the
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``~/.spack/packages.yaml`` file for user configuations, or the
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``etc/spack/packages.yaml`` site configuration.
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Here's an example packages.yaml file that sets preferred packages:
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.. code-block:: yaml
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packages:
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opencv:
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compiler: [gcc@4.9]
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variants: +debug
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gperftools:
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version: [2.2, 2.4, 2.3]
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all:
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compiler: [gcc@4.4.7, gcc@4.6:, intel, clang, pgi]
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providers:
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mpi: [mvapich, mpich, openmpi]
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At a high level, this example is specifying how packages should be
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concretized. The opencv package should prefer using gcc 4.9 and
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be built with debug options. The gperftools package should prefer version
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2.2 over 2.4. Every package on the system should prefer mvapich for
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its MPI and gcc 4.4.7 (except for opencv, which overrides this by preferring gcc 4.9).
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These options are used to fill in implicit defaults. Any of them can be overwritten
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on the command line if explicitly requested.
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Each packages.yaml file begins with the string ``packages:`` and
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package names are specified on the next level. The special string ``all``
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applies settings to each package. Underneath each package name is
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one or more components: ``compiler``, ``variants``, ``version``,
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or ``providers``. Each component has an ordered list of spec
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``constraints``, with earlier entries in the list being preferred over
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later entries.
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Sometimes a package installation may have constraints that forbid
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the first concretization rule, in which case Spack will use the first
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legal concretization rule. Going back to the example, if a user
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requests gperftools 2.3 or later, then Spack will install version 2.4
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as the 2.4 version of gperftools is preferred over 2.3.
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An explicit concretization rule in the preferred section will always
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take preference over unlisted concretizations. In the above example,
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xlc isn't listed in the compiler list. Every listed compiler from
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gcc to pgi will thus be preferred over the xlc compiler.
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The syntax for the ``provider`` section differs slightly from other
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concretization rules. A provider lists a value that packages may
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``depend_on`` (e.g, mpi) and a list of rules for fulfilling that
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dependency.
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