Building Ascent


Ascent uses CMake for its build system. Building Ascent creates two separate libraries:

  • libascent : a version for execution on a single node
  • libascent_mpi : a version for distributed memory parallel

The CMake variable( ENABLE_MPI ON | OFF ) controls the building the parallel version of Ascent and included proxy-apps.

The build dependencies vary according to which pipelines and proxy-applications are desired. For a minimal build with no parallel components, the following are required:

  • Conduit
  • C++ compilers

We recognize that building on HPC systems can be difficult, and we have provid two seperate build strategies.

  • A spack based build
  • Manually compile depencies using a CMake configuration file to keep compilers and libraries consistent

Most often, the spack based build should be attemted first. Spack will automatically download and build all the third party dependencies and create a CMake configuration file for Ascent. Should you encounter build issues that are not addressed here, please ask questions using our github issue tracker.

Build Dependencies



  • Conduit
  • One or more runtimes

For Ascent, the Flow runtime is builtin, but for visualization functionality (filters and rendering), the VTK-h runtime is needed.

Conduit (Required)

  • MPI
  • Python + NumPy (Optional)
  • HDF5 (Optional)
  • Fortran compiler (Optional)

VTK-h (Optional)

  • VTK-h:

    • VTK-m:
      • OpenMP (Optional)
      • CUDA 7.5+ (Optional)
      • MPI (Optional)


When building VTK-m for use with VTK-h, VTK-m must be configured with rendering on, among other options. See the VTK-h spack package for details.

MFEM (Optional)

  • MPI
  • Metis
  • Hypre

Getting Started

Clone the Ascent repo:

  • From Github
git clone --recursive

--recursive is necessary because we are using a git submodule to pull in BLT ( If you cloned without --recursive, you can checkout this submodule using:

cd ascent
git submodule init
git submodule update

Configure a build: is a simple wrapper for the cmake call to configure ascent. This creates a new out-of-source build directory build-debug and a directory for the install install-debug. It optionally includes a host-config.cmake file with detailed configuration options.

cd ascent

Build, test, and install Ascent:

cd build-debug
make -j 8
make test
make install

Build Options

Ascent’s build system supports the following CMake options:

  • BUILD_SHARED_LIBS - Controls if shared (ON) or static (OFF) libraries are built. (default = ON)
  • ENABLE_TESTS - Controls if unit tests are built. (default = ON)
  • ENABLE_DOCS - Controls if the Ascent documentation is built (when sphinx and doxygen are found ). (default = ON)
  • ENABLE_FORTRAN - Controls if Fortran components of Ascent are built. This includes the Fortran language bindings and Cloverleaf3D . (default = ON)
  • ENABLE_PYTHON - Controls if the ascent python module and related tests are built. (default = OFF)
The Ascent python module will build for both Python 2 and Python 3. To select a specific Python, set the CMake variable PYTHON_EXECUTABLE to path of the desired python binary. The ascent python module requires the Conduit python module.
  • ENABLE_OPENMP - Controls if the proxy-apps are configured with OpenMP. (default = OFF)
  • ENABLE_MPI - Controls if parallel versions of proxy-apps and Ascent are built. (default = ON)

We are using CMake’s standard FindMPI logic. To select a specific MPI set the CMake variables MPI_C_COMPILER and MPI_CXX_COMPILER, or the other FindMPI options for MPI include paths and MPI libraries.

To run the mpi unit tests on LLNL’s LC platforms, you may also need change the CMake variables MPIEXEC and MPIEXEC_NUMPROC_FLAG, so you can use srun and select a partition. (for an example see: src/host-configs/chaos_5_x86_64.cmake)


Starting in CMake 3.10, the FindMPI MPIEXEC variable was changed to MPIEXEC_EXECUTABLE. FindMPI will still set MPIEXEC, but any attempt to change it before calling FindMPI with your own cached value of MPIEXEC will not survive, so you need to set MPIEXEC_EXECUTABLE [reference].

  • CONDUIT_DIR - Path to an Conduit install (required for parallel version).
  • VTKM_DIR - Path to an VTK-m install (optional).
  • HDF5_DIR - Path to a HDF5 install (optional).
  • MFEM_DIR - Path to a MFEM install (optional).
  • ADIOS_DIR - Path to a ADIOS install (optional).
  • BLT_SOURCE_DIR - Path to BLT. (default = “blt”)
Defaults to “blt”, where we expect the blt submodule. The most compelling reason to override is to share a single instance of BLT across multiple projects.

Host Config Files

To handle build options, third party library paths, etc we rely on CMake’s initial-cache file mechanism.

cmake -C config_file.cmake

We call these initial-cache files host-config files, since we typically create a file for each platform or specific hosts if necessary.

The script uses your machine’s hostname, the SYS_TYPE environment variable, and your platform name (via uname) to look for an existing host config file in the host-configs directory at the root of the ascent repo. If found, it passes the host config file to CMake via the -C command line option.

cmake {other options} -C host-configs/{config_file}.cmake ../

You can find example files in the host-configs directory.

These files use standard CMake commands. CMake set commands need to specify the root cache path as follows:


It is possible to create your own configure file, and an boilerplate example is provided in /host-configs/boilerplate.cmake


If compiling all of the dependencies yourself, it is important that you use the same compilers for all dependencies. For example, different MPI and Fortran compilers (e.g., Intel and GCC) are not compatible with one another.

Bootstrapping Third Party Dependencies

You can use (located at the root of the ascent repo) to help setup your development environment on OSX and Linux. This script uses scripts/uberenv/, which leverages Spack ( to build the external third party libraries and tools used by Ascent. Fortran support in is optional, dependencies should build without fortran. After building these libraries and tools, it writes an initial host-config file and adds the Spack built CMake binary to your PATH, so can immediately call the helper script to configure a ascent build.

#build third party libs using spack

#copy the generated host-config file into the standard location
cp uberenv_libs/`hostname`*.cmake host-configs/

# run the configure helper script

# or you can run the configure helper script and give it the
# path to a host-config file
./ uberenv_libs/`hostname`*.cmake

Compiler Settings for Third Party Dependencies

You can edit scripts/uberenv/compilers.yaml to change the compiler settings passed to Spack. See the Spack Compiler Configuration documentation for details.

For OSX, the defaults in compilers.yaml are clang from X-Code and gfortran from


The bootstrapping process ignores ~/.spack/compilers.yaml to avoid conflicts and surprises from a user’s specific Spack settings on HPC platforms.


Ascent developers use scripts/uberenv/ to setup third party libraries for Ascent development. Due to this, the process builds more libraries than necessary for most use cases. For example, we build independent installs of Python 2 and Python 3 to make it easy to check Python C-API compatibility during development. In the near future, we plan to provide a Spack package to simplify deployment.

Building with Spack

As of 11/10/2017, Spack’s develop branch includes a recipe to build and install Ascent.

To install Ascent with all options (and also build all of its dependencies as necessary) run:

spack install ascent

To build and install Ascent with CUDA support:

spack install ascent+cuda

The Ascent Spack package provides several variants that customize the options and dependencies used to build Ascent:

Variant Description Default
shared Build Ascent as shared libraries ON (+shared)
cmake Build CMake with Spack ON (+cmake)
python Enable Ascent Python support ON (+python)
mpi Enable Ascent MPI support ON (+mpi)
vtkh Enable Ascent VTK-h support ON (+vtkh)
tbb Enable VTK-h TBB support ON (+tbb)
cuda Enable VTK-h CUDA support OFF (~cuda)
doc Build Ascent’s Documentation OFF (~doc)
doc Enable MFEM support OFF (~mfem)

Variants are enabled using + and disabled using ~. For example, to build Conduit with the minimum set of options (and dependencies) run:

spack install ascent+cuda~python~docs

See Spack’s Compiler Configuration to customize which compiler settings.

Using system installs of dependencies with Spack

Spack allows you to specify system installs of packages using a packages.yaml file.

Here is an example specifying system CUDA on MacOS:

# CUDA standard MacOS install
      cuda@8.0: /Developer/NVIDIA/CUDA-8.0
  buildable: False

Here is an example of specifying system MPI and CUDA on an LLNL Chaos 5 machine:

# LLNL chaos5 CUDA
      cuda@8.0: /opt/cudatoolkit-8.0
    buildable: False
# LLNL chaos5 mvapich for gcc
      mvapich2@2: /usr/local/tools/mvapich2-gnu-2.0/
    buildable: False
Settings for GCC 4.9.3 on LLNL Chaos 5 Systems:

Using Ascent in Another Project

Under src/examples there are examples demonstrating how to use Ascent in a CMake-based build system (using-with-cmake) and via a Makefile (using-with-make). Under src/examples/proxies you can find example integrations using ascent in the Lulesh, Kripke, and Cloverleaf3D proxy-applications. In src/examples/synthetic/noise you can find an example integration using our synthetic smooth noise application.

Building Ascent in a Docker Container

Under src/examples/docker/master/ubuntu there is an example Dockerfile which can be used to create an ubuntu-based docker image with a build of the Ascent github master branch. There is also a script that demonstrates how to build a Docker image from the Dockerfile ( and a script that runs this image in a Docker container ( The Ascent repo is cloned into the image’s file system at /ascent, the build directory is /ascent/build-debug, and the install directory is /ascent/install-debug.

Building Ascent Dependencies Manually

In some environments, a spack build of Ascents dependencies can fail or a user may prefer to build the dependencies manually. This section describes how to build Ascents components. When building Ascents dependencies, it is highly recommended to fill out a host config file like the one located in /host-configs/boilerplate.cmake. This is the best way to avoid problems that can easily arise from mixing c++ standard libraries conflicts, MPI library conflicts, and fortran module conflicts, all of which are difficult to spot. Use the same CMake host-config file for each of Ascent’s dependencies, and while this may bring in unused cmake variables and clutter the ccmake curses interface, it will help avoid problems. In the host config, you can specify options such as ENABLE_PYTHON=OFF, ENABLE_FORTRAN=OFF, and ENABLE_MPI=ON that will be respected by both conduit and ascent.

HDF5 (Optional)

The HDF5 source tarball on the HDF5 group’s website. While the source contains both an autotools configure and CMake build system, use the CMake build system with your host config file. Once you have built and installed HDF5 into a local directory, add the location of that directory to the declaration of the HDF5_DIR in the host config file.

curl > hdf5.tar.gz
tar -xzf hdf5.tar.gz
cd hdf5-1.8.16/
mkdir build
mkdir install
cd build
cmake -C path_to_host_config/myhost_config.cmake . \
make install

In the host config, add set(HDF5_DIR "/path/to/hdf5_install" CACHE PATH "").


The version of conduit we use is the master branch. If the HDF5_DIR is specified in the host config, then conduit will build the relay io library. Likewise, if the config file has the entry ENABLE_MPI=ON, then conduit will build parallel versions of the libraries. Once you have installed conduit, add the path to the install directory to your host config file in the cmake variable CONDUIT_DIR.

git clone --recursive
cd conduit
git checkout tags/v0.3.1
mkdir build
mkdir install
cd build
cmake -C path_to_host_config/myhost_config.cmake ../src \
make install

In the host config, add set(CONDUIT_DIR "/path/to/conduit_install" CACHE PATH "").


Now that we have all the dependencies built and a host config file for our environment, we can now build Ascent.

git clone --recursive
cd ascent
mkdir build
mkdir install
cd build
cmake -C path_to_host_config/myhost_config.cmake . -DCMAKE_INSTALL_PREFIX=path_to_install \
make install

To run the unit tests to make sure everything works, do make test. If you install these dependencies in a public place in your environment, we encourage you to make you host config publicly available by submitting a pull request to the Ascent repo. This will allow others to easily build on that system by only following the Ascent build instructions.

Asking Ascent how its configured

Once built, Ascent has a number of unit tests. t_ascent_smoke, located in the tests/ascent directory will print Ascent’s build configuration:

        "version": "0.4.0",
                "cpp": "/usr/tce/packages/gcc/gcc-4.9.3/bin/g++",
                "fortran": "/usr/tce/packages/gcc/gcc-4.9.3/bin/gfortran"
        "platform": "linux",
        "system": "Linux-3.10.0-862.6.3.1chaos.ch6.x86_64",
        "install_prefix": "/usr/local",
        "mpi": "disabled",
                        "status": "enabled",
                                "status": "enabled",
                                        "serial": "enabled",
                                        "openmp": "enabled",
                                        "cuda": "disabled"
                        "status": "enabled"
        "default_runtime": "ascent"

In this case, the non-MPI version of Ascent was used, so MPI reportsa as disabled.