INSTALL.md

code_saturne installation documentation

The code_saturne tool may be installed either directly through its GNU Autotools based scripts (the traditional configure, make, make install sequence), or using a 2-pass semi-automatic install script (install_saturne.py), which generates an initial setup file when run a first time, and builds and installs code_saturne and some optional libraries based on the edited setup when run a second time.

The semi-automatic and regular installation modes may be combined: after an initial run using the install_saturne.py script, the lower-level autotools may be used to fine-tune the installation.

Preparing for build

Source tree obtained through a source code repository

For users obtaining the code was obtained through a Git repository, an additional step is required:

$ cd code_saturne
$ ./sbin/bootstrap
$ cd ..

In this case, additional tools need to be available:

• GNU Autotools: Autoconf, Automake.
• PdfLaTeX
• Doxygen (1.8.7 or more recent). The path to Doxygen can be specified during the configure phase with configure DOXYGEN=PATH_TO_DOXYGEN.

These tools are not necessary for builds from tarballs; they are called when building the tarball (using make dist), so as to reduce the number of prerequisites for regular users, while developers building the code from a repository can be expected to need a more complete development environment. Also, to build and install the documentation when building the code from a repository instead of a tarball, the following stages are required:

$ make doc
$ make install-doc

Source tree obtained through a tarball

When downloading a .tar.gz file, all that should be necessary is to unpack it:

tar xvzf code_saturne.tar.gz

Source, build, and install directories

3 types of directories are considered when installing the code:

• The source directory is the directory in which the source tree is cloned or unpacked
• The build directory is the directory in which the configuration and compilation will take place
• The install directory is the directory where the usable code will be installed. If unspecified, it will usually be /usr/local or usr.

In the following sections, we will assume a dedicated directory structure is used, for example: /home/user/code_saturne/src for source trees, /home/user/code_saturne/src/build for build trees, and /home/user/code_saturne/arch for installation (so as to keep directories both separate and easy to locate relative to each other). Any directory structure may be chosen, as long as it is easily comprehensible.

It is strongly recommended to build the code in a separate directory from the source (the semi-automatic installer enforces this). This also allows multiple builds, for example, building both an optimized and a debugging version. In this case, choose a consistent naming scheme, using an additional level of sub-directories, for example:

mkdir code_saturne_build
cd code_saturne_build
mkdir prod
cd prod

Also, as installing to a default system directory requires administrator-level write permissions, and is not well adapted to multiple builds, this should be reserved for Linux package maintainers. In all other cases, it is strongly recommended to choose an installation path in a user or project directory. Installing code_saturne does not require root privileges if done correctly.

Semi-automatic installation

The install_saturne.py Python script present in the root directory of the code_saturne source tree allows for semi-automatic installation of code_saturne elements and some associated optional libraries. In most cases, it will be sufficient to obtain a usable build. In case of problems, switching to a regular install is recommended. This script is given in the hope that they it will useful, but is simply a wrapper to the actual build system.

install_saturne.py works in 2 or more passes.

• on the first run, the script attempts to detect some tools, and generates a first setup configuration file;
• The setup file should be checked and modified according to need;
• on subsequent runs, libraries are downloaded and built, and code_saturne is configured or built, based on the setup configuration
• The script can be edited run multiple times, so that steps finished in prior runs do not need to be executed again if they succeeded.

The script can download the main packages needed by the code to run properly. If these packages are not needed, or already present, set the download variable to no in the setup script. If your system already provides adequate versions of these tools, it is usually simpler to use the system-provided ones.

Lastly, the possibility is given to compile code_saturne with debugging symbols (debug variable), and to disable the Graphical User Interface (disable_gui variable).

Due to dependencies between the different modules, the order of install of the optional modules should be the following:

• HDF5
• CGNS
• MED
• PT-Scotch
• ParMETIS

The following packages are not handled by the installer so must be installed first:

• C, C++, and Fortran compilers
• Python
• MPI (optional, strongly recommended)
• PyQt (optional, required for the GUI)
• Zlib (optional)

Using the setup file

As already mentioned, this file is generated the first time the script is run in a given directory.

The C, Fortran, and C++ compilers to be used can be specified next to the compC, compCxx, and compF keywords. The Python interpreter and MPI C and C++ compiler wrappers can also be specified.

If the use_arch variable is set to yes, then the arch keyword refers to the architecture of the machine. If left blank, the name will be based on the uname command. When multiple builds are needed, (such as simply using a production and debug build), arch should be specified for at least one of the builds.

The last section of the file relates to external libraries which can be downloaded, installed, and used by code_saturne.

For each element, there are four options:

• do not use the element (for optional libraries like CGNS) In this case, specify no in the Use and Install columns. The other elements will be installed in accordance. The Path column is not used.

• automatically detect some element In this case, specify auto in the Use column. The other elements will be installed in accordance. The Path and Install column are not used.

• use a pre-installed library in a non standard path In this case, specify yes in the Use column and no in the Install column. The Path column should contain the location of the library (up to the name of the library itself).

• install and use a library In this case, specify yes in the Use and Install columns. The script will download the library and install it default install directory. If download has been set to no, package archive are looked for at the same location than the installation script (the right number and archive name are needed, accordingly to what is prescribed in the script). After each element has been installed, the setup file is modified, the column Install of the concerned element is set to no and the Path column is filled so that the element is not installed a second time if the script is relaunched (if there was a problem with a later element).

Note that when install_saturne.py is run, it generates a build directory, in which the build may be modified (re-running configure, possibly adapting the command logged at the beginning of the config.status file) and resumed.

So after an initial install is done using this script, it is possible to switch to the regular installation to modify options and rebuild the code starting from a first installation scheme.

Recommended post-install steps

Each user of code_saturne may set her/his PATH or define an alias accordingly with the code_saturne installation, to avoid needing to type the full install path name when using the code. The easiest solution is to define a alias in the user's $HOME/.bashrc, $HOME/.alias, or equivalent file (depending on the shell).

alias code_saturne="<install-prefix>/bin/code_saturne"

Note that when multiple versions of the code are installed side by side, using a different alias for each will allow using them simultaneously, with no risk of confusion. Aliases will be usable in a user shell but not in most scripts. With no alias, using the absolute path is always an option.

Using the bash interpreter, automatic code completion help may also be set up, using:

'source <install_prefix>/etc/bash_completion.d/code_saturne`

This may also be defined in a file such as $HOME/.bashrc or $HOME/.bash_profile so as to be usable across sessions.

Global configuration file

For some systems (such as when using a batch system or coupling with SYRTHES), additional post-install step may be required. In this case, copy Copy or rename the <install-prefix>/etc/code_saturne.cfg.template to \ <install-prefix>/etc/code_saturne.cfg, and uncomment and define the applicable sections to adapt the file to your needs.

This is useful for example for:

• Define which batch system is used. The name of the batch system should match one of the templates in <install-prefix>/share/code_saturne/batch, but an absolute path (with a file ending in the given batch system name) can be used to define a batch template tailored to a given system.

• Define compute_versions using the relative paths of alternate builds, so as to be able to use them from a "main" build. All specified builds are then available from the GUI and run script, which is especially useful to switch from a production to a debug build. In this case the secondary builds do not need to contain the full front-end (GUI, documentation, ...).

• Assign a name to the current build or system, so that the run configurations defined for each case (number of processors, batch template, ...) are saved specifically for that system. When using different systems on a same network, this allows keeping track of configurations specific to each system while moving or copying cases from one system to another.

• Defining the path to a SYRTHES installation to enable conjugate heat transfer.

• All default MPI execution commands and options may be overridden using the mpi section. Note that only the options defined in this section are overridden; defaults continue to apply for all others.

For more information on run configurations, please refer to the Doxygen documentation.

Regular installation

The installation scripts of code_saturne are based on the GNU Autotools, (Autoconf and Automake), so it should be familiar for many administrators. A few remarks are given here:

• As with most software with modern build systems, it is recommended to build the code in a separate directory from the sources. This allows multiple builds (for example production and debug), and is considered good practice. Building directly in the source tree is not regularly tested, and is not guaranteed to work, in addition to "polluting" the source directory with build files.
• By default, optional libraries which may be used by code_saturne are enabled automatically if detected in default search paths (i.e. /usr/ and /usr/local. To find libraries associated with a package installed in an alternate path, a --with-<package>=... option to the configure script must given. To disable the use of a library which would be detected automatically, a matching --without-<package> option must be passed to configure instead.
• Most third-party libraries usable by code_saturne are considered optional, and are simply not used if not detected, but the libraries needed by the GUI are considered mandatory, unless the --disable-gui or --disable-frontend option is explicitly used.

When the prerequisites are available, and a build directory created, building and installing code_saturne may be as simple as running:

../../code_saturne/configure
make
make install

The following sections give more details on code_saturne's recommended third-party libraries, configuration recommendations, troubleshooting, and post-installation options. We always assume that we are in build directory separate from sources. In different examples, we assume that third-party libraries used by code_saturne are either available as part of the base system (i.e. as packages in a Linux distribution), as Environment Modules, or are installed under a separate path.

Configuration

code_saturne uses a build system based on the GNU Autotools, which includes its own documentation.

To obtain the full list of available configuration options, run: configure --help.

Note that for all options starting with --enable-, there is a matching option with --disable-. Similarly, for every --with-, --without- is also possible.

Select configuration options, then run configure. For example, if the code's source tree is in /home/user/code_saturne/src/code_saturne:

/home/user/code_saturne/src/code_saturne/configure \
--prefix=/home/user/code_saturne/<version>/arch/prod \
--with-med=/home/user/opt/med-4.1 \
CC=/home/user/opt/mpich-3.3/bin/mpicc FC=gfortran

Most available prerequisites are auto-detected, so to install the code to the default /usr/local sub-directory, a command such as:

../../code_saturne-\verscs/configure

should be sufficient.

Defining compiler flags and associated environment variables

As usual when using an Autoconf-based configure script, some environment variables may be used. configure --help will provide the list of recognized variables. CC, CXX, and FC allow selecting the C; C++, and Fortran compiler respectively (possibly using an MPI compiler wrapper).

Compiler options are usually defined automatically, based on detection of the compiler (and depending on whether --enable-debug was used). This is handled in a config/cs_auto_flags.sh and libple/config/ple_auto_flags.sh scripts. These files are sourced when running configure, so any modification to it will be effective as soon as configure is run. When installing on an exotic machine, or with a new compiler, adapting this file is useful (and providing feedback to the code_saturne development team will enable support of a broader range of compilers and systems in the future.

The usual CPPFLAGS, CFLAGS, FCCFLAGS, LDFLAGS, and LIBS environment variables may also be used, and flags provided by the user are appended to those automatic defined automatically. To completely disable automatic setting of flags, the --disable-auto-flags option may be used.

Compile and install

Once the code is configured, it may be compiled and installed; for example, to compile the code (using 4 parallel threads), then install it:

make -j4 && make install

To compile the documentation, add:

make doc && make install-doc

To clean the build directory, keeping the configuration, use make clean; To uninstall an installed build, use make uninstall. To clear all configuration info, use make distclean (make uninstall will not work after this).

Troubleshooting

If configure fails and reports an error, the message should be sufficiently clear in most case to understand the cause of the error and fix it. Do not forget that for libraries installed using packages, the development versions of those packages are also necessary, so if configure fails to detect a package which you believe is installed, check the matching development package.

Also, whether it succeeds or fails, configure generates a file named config.log, which contains details on tests run by the script, and is very useful to troubleshoot configuration problems. When configure fails due to a given third-party library, details on tests relative to that library are found in the config.log file. The interesting information is usually in the middle of the file, so you will need to search for strings related to the library to find the test that failed and detailed reasons for its failure.

Installing to a system directory

When installing to a system directory in the default library search path, such as /usr or /usr/local, some Linux systems may require running ldconfig as root or sudoer for the code to work correctly.

Compilers and interpreters

For a minimal build of code_saturne on a Linux or Posix system, the requirements are:

• A C compiler, conforming at least to the C11 standard.
• A Fortran compiler, conforming at least to the Fortran 2008 standard.
• A Python interpreter, with Python version 3.4 or above.

For parallel runs, an MPI library is also necessary (MPI-2 or MPI-3 conforming). To build and use the GUI, PyQt 4 or 5 (which in turn requires Qt 4 or 5 and SIP) are required. Other libraries may be used for additional mesh format options, as well as to improve performance. A list of those libraries and their role is given in a dedicated [section](@ref cs_install_list_ext_lib)).

For some external libraries, such as MED, MEDCoupling, and ParaView Catalyst, a C++11 compliant C++ compiler is also required.

In practice, the code is known to build and function properly at least with the GNU compilers 4.4 and above (up to 9.x at this date), Intel compilers 11 and above (up to 2022 at this date), and Clang (tested with 3.7 or above).

Note also that while code_saturne makes heavy use of Python, this is for scripts and for the GUI only; The solver only uses compiled code, so we could for example use a 32-bit version of Python with 64-bit code_saturne libraries and executables. Also, the version of Python used by ParaView/Catalyst may be independent from the one used for building code_saturne.

MPI compiler wrappers

MPI environments generally provide compiler wrappers, usually with names such as mpicc for C, mpicxx for C++, and mpif90 for Fortran 90. Wrappers conforming to the MPI standard recommendations should provide a -show option, to show which flags are added to the compiler so as to enable MPI. Using wrappers is fine as long as several third-party tools do not provide their own wrappers, in which case either a priority must be established. For example, using HDF5's h5pcc compiler wrapper includes the options used by mpicc when building HDF5 with parallel IO, in addition to HDF5's own flags, so it could be used instead of mpicc. On the contrary, when using a serial build of HDF5 for a parallel build of code_saturne, the h5cc and mpicc wrappers contain different flags, so they are in conflict.

Also, some MPI compiler wrappers may include optimization options used to build MPI, which may be different from those we wish to use that were passed.

To avoid issues with MPI wrappers, it is possible to select an MPI library using the --with-mpi option to configure. For finer control, --with-mpi-include and --with-mpi-lib may be defined separately.

Still, this may not work in all cases, as a fixed list of libraries is tested for, so using MPI compiler wrappers remains the simplest and safest solution. Simply use a CC=mpicc or similar option instead of --with-mpi.

There is no need to use an FC=mpif90 or equivalent option: in code_saturne, MPI is never called directly from Fortran code, so Fortran MPI bindings are not necessary nor recommended.

Interaction with system environment modules

On some systems, especially compute clusters, Environment Modules allow the administrators to provide multiple versions of many scientific libraries, as well us compilers or MPI libraries, using the module command. More details on different environment module systems may be found at http://modules.sourceforge.net or https://github.com/TACC/Lmod.

The code_saturne configure script checks for modules loaded with the module command, and records the list of loaded modules. Whenever running that build of code_saturne, the modules detected at installation time will be used, rather than those defined by default in the user's environment. This allows using versions of code_saturne built with different modules safely and easily, even if the user may be experimenting with other modules for various purposes. This is especially useful when different builds use different compiler or MPI versions.

Given this, it is recommended that when configuring and installing code_saturne, only the modules necessary for that build of for profiling or debugging be loaded. Note that as code_saturne uses the module environment detected and runtime instead of the user's current module settings, debuggers requiring a specific module may not work directly under a standard run script if they were not loaded when installing the code.

The detection of environment modules may be disabled using the --without-modules option, or the use of a specified (colon-separated) list of modules may be forced using the --with-modules= option.

Pre-loading an environment

If installing and running code_saturne requires sourcing a given environment or loading environment modules, the --with-shell-env option allows defining the path for a file to source, or if no path is given, loading default modules.

By default, the main code_saturne command is a Python script. When sourcing an environment, a launcher shell script is run first, loads the required environment, then calls Python with the code_saturne.py script.

This is useful mainly when the Python version used is not installed in a default system path, and must be loaded using an environment module, or otherwise sourcing a specific LD_LIBRARY_PATH environment. Otherwise, the main script may fail due to "library not found" issues.

Optional third-party libraries

In addition to an MPI library (for parallelism) and PyQt library (for the GUI), other libraries may be used for additional mesh format options, as well as to improve performance. A list of those libraries and their role is detailed in this section.

Installing third-party libraries for code_saturne

Third-Party libraries usable with code_saturne may be installed in several ways:

• On many Linux systems, most of optional third-party libraries are available through the distribution's package manager.

  Note that distributions usually split libraries or tools into runtime and development packages, and that although some packages are installed by default on many systems, this is generally not the case for the associated development headers. Development packages usually have the same name as the matching runtime package, with a -dev postfix added. Names might also differ slightly. For example, on a Debian system, the main package for Open MPI is openmpi-bin, but libopenmpi-dev must also be installed for the code_saturne build to be able to use the former.

• If not otherwise available, third-party software may be compiled and installed by an administrator or a user. An administrator will choose where software may be installed, but for a user without administrator privileges or write access to usr/local, installation to a user account is often the only option. None of the third-party libraries usable by code_saturne require administrator privileges, so they may all be installed normally in a user account, provided the user has sufficient expertise to install them. This is usually not complicated (provided one reads the installation instructions, and is prepared to read error messages if something goes wrong), but even for an experienced user or administrator, compiling and installing 5 or 6 libraries as a prerequisite significantly increases the time and effort required to install code_saturne.

  Compiling and installing third-party software may still be necessary when no matching packages or Environment Modules are available, or when a more recent version or a build with different options is desired.

• When code_saturne is configured to use the SALOME platform, some libraries included in that platform may be used directly; this is described in the Installation with the SALOME platform section.

List of third-party libraries usable by code_saturne

The list of third-party software usable with code_saturne is provided here:

• PyQt version 4 or 5 is required by the code_saturne GUI. PyQt in turn requires Qt (4 or 5), Python, and SIP. Without this library, the GUI may not be built, although XML files generated with another install of code_saturne may be used.

  If desired, Using Qt for Python (PySide2) instead of PyQt should require a relatively small porting effort, as most of the preparatory work has been done. The development team should be contacted in this case.

• HDF5 is necessary for MED, and may also be used by CGNS.

• CGNS is necessary to read or write mesh and visualization files using the CGNS format, available as an export format with many third-party meshing tools. CGNS version 3.1 or above is required.

• MED-file library is necessary to read or write mesh and visualization files using the MED format, mainly used by the SALOME platform.

• libCCMIO is necessary to read or write mesh and visualization files generated or readable by STAR-CCM+ using its native format. As recent versions of STAR-CCM+ also handle CGNS output, this is deprecated, and CGNS should be preferred.

• Scotch or PT-Scotch may be used to optimize mesh partitioning. Depending on the mesh, parallel computations with meshes partitioned with these libraries may be from 10% to 50% faster than using the built-in space-filling curve based partitioning.

  As Scotch and PT-Scotch are part of the same package and use symbols with the same names, only one of the 2 may be used. If both are detected, PT-Scotch is used. Versions 6.0 and above are supported.

• METIS or ParMETIS are alternative mesh partitioning libraries. These libraries have a separate source tree, but some of their functions have identical names, so only one of the 2 may be used. If both are available, ParMETIS will be used. Partitioning quality is similar to that obtained with Scotch or PT-Scotch.

  Though broadly available, the ParMETIS license is quite restrictive, so PT-Scotch may be preferred (code_saturne may be built with both METIS and Scotch libraries). METIS uses the Apache 2 licence since March 2013, but it seems that the ParMETIS licence has not been updated so far. METIS 5.0 or above and ParMETIS 4.0 or above are supported.

• MEDCoupling provides various coupling and mesh to mesh interpolation and intersection operators, and can be used by code_saturne for various advanced post-processing operations, such as averaging data over a slice, and for pre-processing of immersed boundary definitions. As its name implies, it is part of the MED constellation, and actually contains several libraries, including MEDLoader (for reading and writing of MED files), and the Remapper and ParaMEDMEM librairies for serial and parallel intepolation and projection methods.

• ParaView Catalyst or full ParaView may be used for co-visualization or in-situ visualization. This requires ParaView 5.4 or above, though 5.9 or above is recommended. Note that ParaView must be built with MPI support for Catalyst to be usable.

• Melissa may be used for in-situ statistical analysis and post-processing of ensemble runs.

• EOS 1.11 or above may be used for thermodynamic properties of fluids. it is not currently free, so usually available only to users at EDF, CEA, or organisms participating in projects with those entities.

• CoolProp is a quite recent open source library, which provides pure and pseudo-pure fluid equations of state and transport properties for 122 components (as of version 6.4), mixture properties using high-accuracy Helmholtz energy formulations (or cubic EOS), correlations of properties of incompressible fluids and brines, fast IAPWS-IF97 (Industrial Formulation) for Water/Steam, and cubic equations of state (SRK, PR). Its validation is based at least in part on comparisons with NIST REFPROP.

• SSH-aerosol model represents the physico chemical transformation undergone by aerosols in the troposphere. It is developed by Cerea (joint EDF/ENPC lab) and Ineris, and replaces the SIze REsolved Aerosol Model (SIREAM) available in code_saturne versions 3.2 to 6.0.

• BLAS (Basic Linear Algebra Subroutines) may be used by the cs_blas_test unit test to compare the cost of operations such as vector sums and dot products with those provided by the code and compiler. If no third-party BLAS is provided, code_saturne reverts to its own implementation of BLAS routines, so no functionality is lost here. Optimized BLAS libraries such as Atlas or MKL may be very fast for BLAS3 (dense matrix/matrix operations), but the advantage is usually much less significant for BLAS 1 (vector/vector) operations, which are almost the only ones code_saturne has the opportunity of using. code_saturne uses its own dot product implementation (using a superblock algorithm, for better precision), and y <- ax+y operations, so external BLAS1 are not used for computation, but only for unit testing (so as to be able to compare performance of built-in BLAS with external BLAS).

  The only exception is the Intel MKL BLAS, which may also be used for sparse matrix-vector products, and is linked with the solver when available. It is then used at runtime on a case per case basis based on initial performance timings.

  Note that in some cases, threaded BLAS routines might oversubscribe processor cores in some MPI calculations, depending on the way both code_saturne and the BLAS were configured and interact, and this can actually lead to lower performance. Use of BLAS libraries is thus useful as a unit benchmarking feature, but has no influence on full calculations. Note also that BLAS may be used indirectly by linear algebra libraries which may make a better use of them, but this is mostly transparent to the code_saturne install.

• PETSc (Portable, Extensible Toolkit for Scientific Computation), consists of a variety of libraries, which may be used by code_saturne for the resolution of linear equation systems. In addition to providing many solver options, it may be used as a bridge to other major solver libraries. Currently, only PETSc using install structures based using the --prefix configure option are correctly detected by the code_saturne build scripts.

• HYPRE (high performance preconditioners) is a library of high performance preconditioners and solvers featuring multigrid methods for the solution of large, sparse linear systems of equations on massively parallel computers.

• AmgX is a high performance multigrid and preconditioned iterative method library for NVIDIA GPUs. It includes a flexible solver composition system that allows a user to easily construct complex nested solvers and preconditioners.

• The SYRTHES code may be used for conjugate heat transfer.

For developers, the GNU Autotools (Autoconf and Automake) will be necessary. To build the documentation, pdfLaTeX, and Doxygen are needed, and dot (from Graphviz) recommended.

PLE (Parallel Location and Exchange) Library

By default, the PLE library is built as a subset of code_saturne, but a standalone version may be configured and built, using the libple/configure script from the code_saturne source tree, instead of the top-level configure script. In this case, code_saturne may then be configured to use an existing install of PLE using the --with-ple configure option.

Special notes on some third-party tools and libraries

Python and PyQt

The GUI is written in PyQt (Python bindings for Qt), so Qt (version 4 or 5) and the matching Python bindings must be available. On most modern Linux distributions, this is available through the package manager, which is by far the preferred solution.

On systems on which both PyQt4 and Pyqt5 are available, PyQt5 will be selected by default, but the selection may be forced by defining QT_SELECT=4 or QT_SELECT=5.

When running on a system which does not provide these libraries, there are several alternatives:

• build code_saturne without the GUI. XML files produced with the GUI are still usable, so if an install of code_saturne with the GUI is available on an other machine, the XML files may be copied on the current machine. This is not an optimal solution, but in the case where users have a mix of desktop or virtual machines with full Linux desktop including PyQt installed, and a compute cluster with a more limited or older system, this may avoid requiring a build of Qt and PyQt on the cluster if users find this too daunting.

• Install a local Python interpreter, and add Qt5 bindings to this interpreter.

  Python and Qt must be downloaded and installed first, in any order. The installation instructions of both of these tools are quite clear, and though the installation of these large packages (especially Qt) may be a lengthy process in terms of compilation time, but is well automated and usually devoid of nasty surprises.

  Once Python is installed, the SIP bindings generator must also be installed. This is a small package, and configuring it simply requires running python configure.py in its source tree, using the Python interpreter just installed.

  Finally, the PyQt bindings, in a manner similar to SIP.

  When this is finished, the local Python interpreter contains the PyQt bindings, and may be used by code_saturne's configure script by passing PYTHON=<path_to_python_executable.

• add Python Qt bindings as a Python extension module for an existing Python installation. This is a more elegant solution than the previous one, and avoids requiring rebuilding Python, but if the user does not have administrator privileges, the extensions will be placed in a directory that is not on the default Python extension search path, and that must be added to the PYTHONPATH environment variable. This works fine, but for all users using this build of code_saturne, the PYTHONPATH environment variable will need to be set.

  The process is similar to the previous one, but SIP and PyQt installation requires a few additional configuration options in this case. See the SIP and PyQt reference guides for detailed instructions, especially the Building a Private Copy of the SIP Module` section of the SIP guide.

Scotch and PT-Scotch

Note that both Scotch and PT-Scotch may be built from the same source tree, and installed together with no name conflicts.

For better performance, PT-Scotch may be built to use threads with concurrent MPI calls. This requires initializing MPI with MPI_Init_thread with MPI_THREAD_MULTIPLE (instead of the more restrictive MPI_THREAD_SERIALIZED, MPI_THREAD_FUNNELED, or MPI_THREAD_SINGLE, or simply using MPI_Init). As code_saturne does not currently require thread models in which different threads may call MPI functions simultaneously, and the use of MPI_THREAD_MULTIPLE may carry a performance penalty, we prefer to sacrifice some of PT-Scotch's * performance by requiring that it be compiled without the -DSCOTCH_PTHREAD flag. This is not detected at compilation time, but with recent MPI libraries, PT-Scotch 6.0 will complain at run time if it notices that the MPI thread safety level in insufficient. PT-Scotch 7.0 uses a more dynamic configuration and does not complain, but its documentation still recommends against this.

Detailed build instructions, including troubleshooting instructions, are given in the source tree's INSTALL.txt file. In case of trouble, note especially the explanation relative to the dummysizes executable, which is run to determine the sizes of structures. On machines with different front-end and compute node architectures, it may be necessary to start the build process, let it fail, run this executable manually using mpiexec}, then pursue the build process.

Note that PT-Scotch may be installed by code_saturne's semi-automatic installer, which chooses settings that should work on most machines.

MED-file

The MED-file library can be built using either CMake or the GNU Autotools. The Autotools installation of MED is simple on most machines, but a few remarks may be useful for specific cases.

Note that while MED 4.x uses HDF5 1.10 while MED 5.x requires HDF5 1.12.

MED has a C API, is written in a mix of C and C++ code, and provides both a C (libmedC) and an Fortran API (libmed) by default (i.e. unless the --disable-fortran configure option is used. code_saturne only requires the C API.

When building MED in a cross-compiling situation, --med-int=int or --med-int=int64_t (depending on whether 32 or 64 bit ids should be used) should be passed to its configure script to avoid a run-time test.

libCCMIO

Different versions of this library may use different build systems, and use different names for library directories, so using both the --with-ccm= or --with-ccm-include= and --with-ccm-lib= options to configure is usually necessary. Also, the include directory should be the toplevel library, as header files are searched under a libccmio subdirectory. This is made necessary by libCCMIO version 2.6.1, in which this is hard-coded in headers including other headers. In more recent versions such as 2.06.023, this is not the case anymore, and an include subdirectory is present, but it does not contain the libccmioversion.h file, which is found only under the libccmio subdirectory, but is required by code_saturne to handle differences between versions, so that source directory is preferred to the installation include.

A libCCMIO distribution usually contains precompiled binaries, but recompiling the library is recommended. Note that at least for version 2.06.023, the build will fail building dump utilities, due to the -l adf option being placed too early in the link command. To avoid this, add LDLIBS=-ladf to the makefile command, for example:

make -f Makefile.linux SHARED=1 DEBUG=1 LDLIBS=-ladf

SHARED=1 and DEBUG=1 may be used to force shared library or debug builds respectively, but some issues have been observed on some systems using non-debug builds, so adding that option is recommended.

Finally, if using libCCMIO 2.6.1, remove the libcgns* files from the libCCMIO libraries directory if also building code_saturne with CGNS support, as those libraries are not required for CCMIO, and are an obsolete version of CGNS, which may interfere with the version used by code_saturne.

Note that libCCMIO uses a modified version of CGNS's ADF library, which may not be compatible with that of CGNS. When building with shared libraries, the reader for libCCMIO uses a plugin architecture to load the library dynamically. For a static build with both libCCMIO and CGNS support, reading ADF-based CGNS files may fail. To work around this issue, CGNS files may be converted to HDF5 using the adf2hdf utility (from the CGNS tools). By default, CGNS post-processing output files use HDF5, so this issue is rare on output.

CoolProp

This library's build system is based on CMake, and building it is straightforward. CoolProp uses submodules which are downloaded using git clone https://github.com/CoolProp/CoolProp.git --recursive.

Its user documentation is good, but its installation documentation not so much, so recommendations are provided here

To download and prepare CoolProp for build, using an out-of-tree build (so as to avoid polluting the source tree with cache files), the following commands are recommended:

git clone https://github.com/CoolProp/CoolProp.git --recursive
cd CoolProp
git checkout release
cd ..
mkdir CoolProp_build
cd CoolProp_build

Then configure, build, and install, run:

cmake \
-DCOOLPROP_INSTALL_PREFIX=${INSTALL_PATH} \
-DCOOLPROP_SHARED_LIBRARY=ON \
-DCMAKE_BUILD_TYPE=Release \
${COOLPROP_SRC_PATH}

Followed by:

make
make install
make clean

To install CoolProp's Python bindings (used by the GUI when available), the straigthforward method is to go into the CoolProp source directory, into the wrappers/Python subdirectory, then run:

export PYTHONPATH=${COOLPROP_INSTALL_PREFIX}/lib64/${python_version}/site-packages:$PYTHONPATH
python setup.py install --prefix=${COOLPROP_INSTALL_PREFIX}

Although this is not really an out-of-tree build, the Python setup also cleans the directory.

Note that Python bindings will install the CoolProp libraries and headers in a slightly different structure, so this must be accounted for when specifying the CoolProp installation paths.

MEDCoupling

To download MEDCoupling, the following commands can be used.

git clone -b V9_10_0 https://git.salome-platform.org/gitpub/tools/configuration
git clone -b V9_10_0 https://git.salome-platform.org/gitpub/tools/medcoupling

The -b V9_10_0 option used here indicates we want to use version 9.10.0. It can be omitted for the development version, or another tag (such as the newer V9_11_0) may be used instead.

Once these libraries are downloaded, a separate build directory should be created, as usual:

mkdir MEDCoupling_build
cd MEDCoupling_build

Then a MEDCoupling may be built and installed with the following command:

cmake -DCMAKE_INSTALL_PREFIX=${INSTALL_PATH} \
-DCONFIGURATION_ROOT_DIR=${CONFIGURATION_SRC_PATH} \
-DMEDCOUPLING_BUILD_DOC=OFF \
-DMEDCOUPLING_BUILD_TESTS=OFF \
-DMEDCOUPLING_ENABLE_PARTITIONER=OFF \
-DMEDCOUPLING_ENABLE_RENUMBER=OFF \
-DMEDCOUPLING_USE_MPI=ON \
-DMEDFILE_ROOT_DIR=${MED_INSTALL_PATH} \
-DHDF5_ROOT_DIR=${HDF5_INSTALL_PATH} \
-DHDF5_INCLUDE_DIR=${HDF5_INSTALL_PATH}include \
${MEDCOUPLING_SRC_PATH}
make && make install && make clean

As an alternative, if reading and writing of MED files is not needed, and only the coupling and intersection features are desired, a lighweight install may be obtained with:

cmake -DCMAKE_INSTALL_PREFIX=${INSTALL_PATH} \
-DCONFIGURATION_ROOT_DIR=${CONFIGURATION_SRC_PATH} \
-DMEDCOUPLING_BUILD_DOC=OFF \
-DMEDCOUPLING_BUILD_TESTS=OFF \
-DMEDCOUPLING_ENABLE_PARTITIONER=OFF \
-DMEDCOUPLING_ENABLE_RENUMBER=OFF \
-DMEDCOUPLING_USE_MPI=ON \
-DMEDCOUPLING_MICROMED=ON \
${MEDCOUPLING_SRC_PATH}
make && make install && make clean

Paraview Catalyst

By default, this library is built with a GUI, but it may also be be built using OSMesa or EGL for offscreen rendering. The build documentation on the ParaView website and Wiki details this. On a workstation, a regular build of ParaViw with MPI support may be sufficient.

For a compute cluster or server in which code_saturne will run outside a graphical (X11) environment, the recommended solution is to build or use a standard ParaView build for interactive visualization, and to use its Catalyst/Define Exports option to generate Python co-processing scripts. A second build, using OSMesa (or EGL), may be used for in-situ visualization. This is the Version code_saturne will be linked to. A recommended cmake command for this build contains:

cmake \
-DCMAKE_INSTALL_PREFIX=${INSTALL_PATH}_osmesa \
-DPARAVIEW_USE_QT=OFF \
-DPARAVIEW_USE_MPI=ON \
-DPARAVIEW_USE_PYTHON=ON \
-DPARAVIEW_INSTALL_DEVELOPMENT_FILES=ON \
-DOSMESA_INCLUDE_DIR=${MESA_INSTALL_PREFIX}/include \
-DOSMESA_LIBRARY=${MESA_INSTALL_PREFIX}/lib/libOSMesa.so \
-DVTK_OPENGL_HAS_OSMESA=ON \
-DVTK_USE_X=OFF \
${PARAVIEW_SRC_PATH}

More info may also be found on the ParaView Wiki.

Note that when ParaView uses libraries which are in non-standard locations, it may be necessary to specify those locations in the CMake prefix path for ParaView detection by code_saturne. Actually, the option passed to --with-catalyst when running code_saturne's configure step is the CMAKE_PREFIX_PATH, so if multiple directories need to be included, an enquoted and semicolon-separated path may be used, for example:

--with-catalyst="/home/user/opt/paraview-5.11;/home/user/opt/ospray2"

Also, if the detection of Catalyst fails due to incorrect detection of the TBB library, the TBB_INCLUDE_DIR environment variable may be set to pass the correct path to the configuration scripts.

On at least one system (with RHEL 8.3 and the gcc 8.3.1 compiler), a crash at finalization of Catalyst has been observed. If this is the case, setting the CS_PV_CP_DELETE_CRASH_WORKAROUND environment variable to 1 should avoid calling the offending code.

Coupling with SYRTHES

Coupling with SYRTHES requires defining the path to a SYRTHES installation at the post-install stage (in the code_saturne.cfg file).

Both code_saturne and SYRTHES must use the same MPI library, and must use the same major version of the PLE library from code_saturne. If SYRTHES is installed after code_saturne, the simplest solution is to configure its build to use the PLE library from the existing code_saturne install.

Specific build types

Debug builds

It may be useful to install debug builds alongside production builds of code_saturne, especially when user-defined functions are used and the risk of crashes due to user programming error is high. Running the code using a debug build is significantly slower, but more information may be available in the case of a crash, helping understand and fix the problem faster.

Here, having a consistent and practical naming scheme is useful. For a side-by-side debug build for the initial example, we simply replace prod by dbg in the --prefix option, and add: --enable-debug to the configure command:

cd ..
mkdir dbg
cd dbg
../../code_saturne/configure \
--prefix=/home/user/code_saturne/<version>/arch/dbg \
--with-med}=/home/user/opt/med-4.1 \
--enable-debug \
CC=/home/user/opt/mpich-3.3/bin/mpicc FC=gfortran

Shared or static builds

By default, on most architectures, code_saturne will be built with shared libraries. Shared libraries may be disabled (in which case static libraries are automatically enabled) by adding --disable-shared to the options passed to configure. On some systems, the build may default to static libraries instead.

It is possible to build both shared and static libraries by not adding --disable-static to the configure options, but the executables will be linked with the shared version of the libraries, so this is rarely useful (the build process is also slower in this case, as each file is compiled twice).

In some cases, a shared build may fail due to some dependencies on static-only libraries. In this case, --disable-shared will be necessary. Disabling shared libraries is also necessary to avoid issues with linking user functions on Mac OS-X systems.

In any case, be careful if you switch from one option to the other: as linking will be done with shared libraries by default, a build with static libraries only will not completely overwrite a build using shared libraries, so uninstalling the previous build first is recommended.

Relocatable builds

By default, a build of code_saturne is not movable, as not only are library paths hard-coded using rpath type info, but the code's scripts also contain absolute paths.

To ensure a build is movable, pass the --enable-relocatable option to configure.

Movable builds assume a standard directory hierarchy, so when running configure, the --prefix option may be used, but fine tuning of installation directories using options such as --bindir, --libdir, or --docdir must not be used (these options are useful to install to strict directory hierarchies, such as when packaging the code for a Linux distribution, in which case making the build relocatable would be nonsense anyways, so this is not an issue.

Remark: for relocatable builds using ParaView/Catalyst, a CATALYST_ROOT_DIR environment variable may be used to specify the Catalyst location in case that was moved also.

For package maintainers

In the special case of packaging the code, which may require both fine-grained control of the installation directories and the possibility to support options such as dpkg's --instdir, it is assumed the packager has sufficient knowledge to update both rpath information and paths in scripts in the executables and python package directories of a non-relocatable build, and that the packaging mechanism includes the necessary tools and scripts to enable this.

Remarks for large meshes

If code_saturne is to be run on large meshes, several precautions regarding its configuration and that of third-party software must be taken.

in addition to local connectivity arrays, code_saturne uses global element ids for some operations, such as reading and writing meshes and restart files, parallel interface element matching, and post-processing output. For a hexahedral mesh with N cells, the number of faces is about 3N (6 faces per cell, shared by 2 cells each). With 4 cells per face, the face to vertices array is of size of the order of 4 * 3N, so global ids used in that array's index will reach 2³¹ for a mesh in the range of 2³¹ / 12 (approximately 178 million cells). In practice, we have encountered a limit with slightly smaller meshes.

Above 150 million hexahedral cells or so, it is thus imperative to configure the build to use 64-bit global element ids. This is the default. Local indexes use the default int size. To slightly decrease memory consumption if meshes of this size are never expected (for example on a workstation or a small cluster), the --disable-long-gnum option may be used.

Recent versions of some third-party libraries may also optionally use 64-bit ids, independently of each other or of code_saturne. This is the case for the Scotch, METIS, MED and CGNS libraries. In the case of graph-based partitioning, only global cell ids are used, so 64-bit ids should not in theory be necessary for meshes under 2 billion cells. In a similar vein, for post-processing output using nodal connectivity, 64-bit global ids should only be an imperative when the number of cells or vertices approaches 2 billion. Practical limits may be lower, if some intermediate internal counts reach these limits earlier.

Partitioning a 158 million hexahedral mesh using serial METIS 5 or Scotch on a front-end node with 128 Gb memory is possible, but partitioning the same mesh on cluster nodes with "only" 24 Gb each may not, so using parallel partitioning PT-Scotch or ParMETIS should be preferred.

Installation with the SALOME platform

To simplify the detection of some libraries provided with a [SALOME platform] (http://www.salome-platform.org) installation, the --with-salome configuration option may be used, so as to specify the directory of the SALOME installation (note that in the case of older SALOME builds with a separate application directory, this should be the main installation directory, not the default application directory, also generated by SALOME's installers).

Specifying a SALOME directory sets the default search paths for the HDF5, MED, MEDCoupling, and CGNS libraries to those provided by the SALOME environment. The default search path for ParaView Catalyst is also set to that provided by the SALOME environment, but since not all SALOME builds of ParaView may support Catalyst (which requires MPI and Python support, along with development headers), enabling ParaView Catalyst support also requires providing the --with-catalyst configure option, without speciifying a path.

When those libraries are available as system packages and not inside the SALOME directory, some of these options might not be available.

If desired, to ensure that the versions defined by SALOME are used, the following configuration options may also be used for HDF5, CGNS, MED, MEDCoupling, and ParaView Catalyst respectively:

--with-hdf5=salome
--with-cgns=salome
--with-med=salome
--with-medcoupling=salome
--with-catalyst=salome

Also, if SALOME provides its own CMake binary, it will be used instead of the default system version, unless CMAKE=cmake or CMAKE=<path_to_cmake> is specified, as it is expected to be at least as recent as that of the target system.

As CGNS and MED file formats are portable, MED or CGNS files produced by either code_saturne or SALOME remain interoperable. At the least, files produced with a given version of CGNS or MED should be readable with the same or a newer version of that library.

Also note that for SALOME builds containing their own Python interpreter and library, using that same interpreter for code_saturne may avoid some issues with Python-based tools, but may then require sourcing the SALOME environment or at least its Python-related LD_LIBRARY_PATH for the main code_saturne script to be usable. The --with-shell-ext configure option of code_saturne is useful here.

Combining SALOME and user-specified libraries.

To use a version of one of these libraries or tools not provided by the chosen SALOME environment, simply specify it in the usual manner using the --with-hdf5, --with-med, --with-medcoupling, --with-cgns, or --with-catalyst configure options to provide the appropriate paths, or turn off support replacing --with by --without.

An alternative approach is to define the matching HDF5_ROOT_DIR, MEDFILE_ROOT_DIR, MEDCOUPLING_ROOT_DIR, CGNS_ROOT_DIR, or PARAVIEW_ROOT_DIR environment variables. If set, those definitions supersede the ones provided by SALOME, and are superseded by the --with-<library> configure options. This may be useful for build scripts combining multiple environemnt elements.

In any case, if the selected HDF5 and dependent libraries (MED and CGNS) do not match, errors may occur either during the configure stage or when running code_saturne.

SALOME platform extensions

The SALOME platform extensions are now provided in a separate repository, with a public mirror at https://github.com/code-saturne/salome_cfd_extensions. They can be installed separately once the main code_saturne install is completed (though in fact installation order is not important).

These extensions contain the CFDSTUDY salome module (available by running salome_cfd after install), which provide workbench integration and links with the OpenTURNS and the PERSALYS graphical interface for sensitivity studies.

To simply use code_saturne from a salome shell session, these extensions are not necessary.

Note finally that SALOME expects a specific directory tree when loading modules, so salome_cfd extensions might fail when installing with a specified (i.e. non-default) --datarootdir path in the code_saturne configure options.

Configuration command examples

For the following advanced examples, Let us define environment variables respectively reflecting the code_saturne source path, installation path, and a path where optional libraries are installed:

SRC_PATH=/home/projects/code_saturne/<x.y>/src/code_saturne-<x.y.z>
INSTALL_PATH=/home/projects/code_saturne/<x.y>
CS_OPT=/home/projects/opt

Here, we have a general /home/projects/code_saturne directory for all code_saturne directories, with a x.y directory for each (major.minor) version, including src and arch subdirectories for sources and installations respectively. Only the installation directories are needed to use the code, but keeping the sources nearby may be practical for reference.

For an install on which multiple versions and architectures of the code should be available, configure commands with all bells and whistles (except SALOME support) for a build on a cluster named gaia}, using the Intel compilers (made available through environment modules) may look like this:

module purge
module load intel_compilers/2019.0.045
module load open_mpi/gcc/4.0.1
${SRC_PATH}/configure \
--prefix=${INSTALL_PATH}/arch/gaia_ompi \
--with-blas=/opt/mkl-2019.0.045/mkl \
--with-hdf5=${CS_OPT}/hdf5-1.10/arch/gaia \
--with-med=${CS_OPT}/med-4.1/arch/gaia \
--with-cgns=${CS_OPT}/cgns-4.2/arch/gaia \
--with-scotch=${CS_OPT}/scotch-7.0/arch/gaia_ompi \
--with-metis=${CS_OPT}/parmetis-4.0/arch/gaia_ompi \
--with-eos/${CS_OPT}/eos-1.11.0/arch/gaia_ompi \
CC=mpicc FC=ifort CXX=mpicxx

In the example above, we have appended the _ompi postfix to the architecture name for libraries using MPI, in case we intend to install 2 builds, with different MPI libraries (such as Open MPI and MPICH-based Intel MPI). Note that optional libraries using MPI must also use the same MPI library. This is the case for PT-Scotch or ParMETIS, but also HDF5, CGNS, and MED if they are built with MPI-IO support. Similarly, C++ and Fortran libraries, and even C libraries built with recent optimizing C compilers, may require runtime libraries associated to that compiler, so if versions using different compilers are to be installed, it is recommended to use a naming scheme which reflects this. In this example, HDF5, CGNS and MED were built without MPI-IO support, as code_saturne does not yet exploit MPI-IO for these libraries.

To avoid copying platform-independent data (such as the documentation) from different builds multiple times, we may use the same --datarootdir option for each build so as to install that data to the same location for each build. In this case, we recommend --datarootdir=${INSTALL_PATH}/share to add a share directory alongside arch.

Cross-compiling

On machines with different front-end and compute node architectures, cross-compiling may be necessary. To install and run code_saturne, 2 builds are then required:

• a front-end build, based on front-end node's architecture. This is the build whose code_saturne command, GUI, and documentation will be used, and with which meshes may be imported (i.e. whose Preprocessor will be used). This build is not intended for calculations, though it could be used for mesh quality criteria checks. This build will thus usually not need MPI.
• a compute build, cross-compiled to run on the compute nodes. This build does not need to include the GUI, documentation, or even the preprocessor module (see user documentation).

A debug variant of the compute build is also recommended, as always. Providing a debug variant of the front-end build is not generally useful.

A post-install step (see Post-install setup) will allow the scripts of the front-end build to access the compute build in a transparent manner, so it will appear to the users that they are simply working with that build.

Depending on their role, optional third-party libraries should be installed either for the front-end, for the compute nodes, or both:

• BLAS will be useful only for the compute nodes, and are generally always available on large compute facilities.
• Python and PyQt will run on the front-end node only.
• HDF5, MED, CGNSlib, and libCCMIO may be used by the Preprocessor on the front-end node to import meshes, and by the main solver on the compute nodes to output visualization meshes and fields.
• Scotch or METIS may be used by a front-end node build of the solver, as serial partitioning of large meshes requires a lot of memory.
• PT-Scotch or ParMETIS may be used by the main solver on the compute nodes.

Compiling for Cray X series

For Cray X series, when using the GNU compilers, installation should be similar to that on standard clusters. Using The Cray compilers, options such as in the following example are recommended:

${SRC_PATH}/configure \
--prefix=${INSTALL_PATH}/arch/xc30 \
--with-hdf5=${CS_OPT}/hdf5-1.10/arch/xc30 \
--with-med}=${CS_OPT}/med-4.1/arch/xc30 \
--with-cgns}=${CS_OPT}/cgns-4.2/arch/xc30 \
--with-scotch}=${CS_OPT}/scotch-7.0/arch/xc30 \
--disable-sockets \
--disable-shared \
--host=x86_64-unknown-linux-gnu \
CC=craycc CXX=crayc++ FC=crayftn

In case the automated environment modules handling causes issues, adding the --without-modules option may be necessary. In that case, caution must be exercised so that the user will load the same modules as those used for installation. This is not an issue if modules for code_saturne is also built, and the right dependencies handled at that level.

Note that to build without OpenMP with the Cray compilers, CFLAGS=-h noomp and FCFLAGS=-h noomp need to be added.

Caveats

Moving an existing installation

Never move a non-relocatable installation of code_saturne.

Using LD_LIBRARY_PATH or LD_PRELOAD may allow the executable to run despite rpath info not being up-to-date, but in environments where different library versions are available, there is a strong risk of not using the correct library. In addition, the scripts will not work unless paths in the installed scripts are updated.

To build a relocatable installation, see the Relocatable builds section.

If you are packaging the code and need both fine-grained control of the installation directories, and the possibility to support options such as dpkg's --instdir, it is assumed you have sufficient knowledge to update both rpath information and paths in scripts in the executables and python package directories, and that the packaging mechanism includes the necessary tools and scripts to enable this.

In any other case, you should not even think about moving a non-relocatable (i.e. default) instead of using a relocatable one.

If you need to test an installation in a test directory before installing it in a production directory, use the make install DESTDIR=<test_prefix> provided by the Autotools mechanism rather than configuring an install for a test directory and then moving it to a production directory. Another less elegant but safe solution is to configure the build for installation to a test directory, and once it is tested, re-configure the build for installation to the final production directory, and rebuild and install.

Dynamic linking and path issues on some systems

On Linux and Unix-like systems, there are several ways for a library or executable to find dynamic libraries, listed here in decreasing priority:

• the LD_PRELOAD environment variable explicitly lists libraries to be loaded with maximum priority, before the libraries otherwise specified (useful mainly for instrumentation and debugging, and should be avoided otherwise);
• the RPATH binary header of the dependent library or executable; (if both are present, the library has priority);
• the LD_LIBRARY_PATH environment variable;
• the RUNPATH binary header of executable;
• /etc/ld.so.cache};
• base library directories (/lib and //usr/lib);

Note that changing the last two items usually require administrator privileges, and we have encountered cases where installing to //usr/lib was not sufficient without updating /etc/ld.so.cache. We do not consider LD_PRELOAD here, as it has other specific uses.

So basically, when using libraries in non-default paths, the remaining options are between RPATH or RUNPATH binary headers, or the LD_LIBRARY_PATH environment variable.

The major advantage of using binary headers is that the executable can be run without needing to source a specific environment, which is very useful, especially when running under MPI (where the propagation of environment variables may depend on the MPI library and batch system's configuration), or running under debuggers (where library paths would have to be sourced first).

In addition, the RPATH binary header has priority over LD_LIBRARY_PATH, allowing the installation to be "protected" from settings in the user environment required by other tools. this is why the code_saturne installation chooses this mode by default, unless the --enable-relocatable option is passed to configure.

Unfortunately, the ELF library spec indicates that the use of the DT_RPATH entry (for RPATH) has been superseded by the DT_RUNPATH (for RUNPATH}). Most systems still use RPATH}, but some (such as SUSE and Gentoo) have defaulted to RUNPATH, which provides no way of "protecting" an executable or library from external settings.

Also, the --enable-new-dtags linker option allows replacing RPATH with RUNPATH}, so adding -Wl,--enable-new-dtagsto theconfigure` options will do this.

The addition of RUNPATH to the ELF specifications may have corrected the oversight of not being able to supersede an executable's settings when needed (though LD_PRELOAD is usually sufficient for debugging, but the bright minds who decided that it should replace RPATH and not simply supplement it did not provide a solution for the following scenario:

• code_saturne in installed, along with the MED and HDF libraries, on a system where --enable-new-dtags is enabled by default.
• Another code is installed, with its own (older) versions of MED and HDF libraries; this second code requires sourcing environment variables including LD_LIBRARY_PATH to work at all, so the user adds those libraries to his environment (or the admins add it to environment modules).
• code_saturne now uses the older libraries, and is not capable of reading files generated with more recent versions

The aforementioned scenario occurs with code_saturne and rpath, on some machines, and could occur with code_saturne and some SALOME libraries, and there is no way around it short of changing the installation logic of these other tools, or using a cumbersome wrapper to launch code_saturne, which could still fail when code_saturne needs to load a rpath or SALOME environment for coupled cases. A wrapper would lead to its own problems, as for example Qt is needed by the GUI but not the executable, so to avoid causing issues with a debugger using its own version of Qt, separate sections would need to be defined. None of those issues exist with RPATH.

To avoid most issues, the code_saturne scripts also update LD_LIBRARY_PATH before calling executable modules, but you could be affected if running them directly from the command line.