The NEURON build system now uses cmake as of version 7.8 circa Nov 2019. The previous autotools (./configure) build system is still supported for the time being but any features that use submodules would need to build those separately.

git clone nrn
cd nrn
mkdir build
cd build
cmake .. # default install to /usr/local
make -j
sudo make -j install

The -j option to make invokes a parallel make using all available cores. This is often very much faster than a single process make. One can add a number after the -j (e.g. make -j 6) to specify the maximum number of processes to use. This can be useful if there is the possibility of running out of memory.

Sadly, there is no equivalent in cmake to the autotool’s ./configure --help to list all the options. The closest is cmake .. -LH which runs cmake .. as above and lists the cache variables along with help strings which are not marked as INTERNAL or ADVANCED. Alternatively,

ccmake ..

allows one to interactively inspect cached variables. In the build folder, cmake -LH (missing <path-to-source) will not run cmake, but if there is a CMakeCache.txt file, the cache variables will be listed.

The above default cmake .. specifies a default installation location and build type, and includes (or leaves out) the following major functional components.

cmake .. -DCMAKE_INSTALL_PREFIX=/usr/local \

Cmake option values persist with subsequent invocations of cmake unless explicitly changed by specifying arguments to cmake (or by modifying them with ccmake). It is intended that all build dependencies are taken into account so that it is not necessary to start fresh with an empty build folder when modifying cmake arguments. However, there may be unknown exceptions to this (bugs) so in case of problems it is generally sufficient to delete all contents of the build folder and start again with the desired cmake arguments.

General options

First arg is always <path-to-source> which is the path (absolute or relative) to the top level nrn folder (e.g. cloned from github). It is very common to create a folder named build in the top level nrn folder and run cmake in that. e.g.

cd nrn
mkdir build
cd build
cmake .. <more args>


Install path prefix, prepended onto install directories. This can be a full path or relative. Default is /usr/local . A common install folder is ‘install’ in the build folder. e.g.


so that the installation folder is .../nrn/build/install . In this case the user should prepend .../nrn/build/install/bin to PATH and it may be useful to

export PYTHONPATH=.../nrn/build/install/lib/python

where in each case ... is the full path prefix to nrn.


Empty or one of Custom;Debug;Release;RelWithDebInfo;Fast.

  • RelWithDebInfo means to compile using -O2 -g options.
  • Debug means to compile with just -g (and optimization level -O0) This is very useful for debugging with gdb as, otherwise, local variables may be optimized away that are useful to inspect.
  • Release means to compile with -O2 -DNDEBUG. The latter eliminates assert statements.
  • Custom requires that you specify flags with CMAKE_C_FLAGS and CMAKE_CXX_FLAGS
  • Fast requires that you specify flags as indicated in nrn/cmake/ReleaseDebugAutoFlags.cmake

Custom and Fast depend on specific compilers and (super)computers and are tailored to those machines. See nrn/cmake/ReleaseDebugAutoFlags.cmake

InterViews options



Unless you specify IV_DIR, InterViews will be automatically cloned as a subproject, built, and installed in CMAKE_INSTALL_PREFIX.


The directory containing a CMake configuration file for iv.

IV_DIR is the install location of iv and the directory actually containing the cmake configuration files is IV_DIR/lib/cmake. This is useful when you have many clones of nrn for different development purposes and wish to use a single independent InterViews installation for many/all of them. E.g. I generally invoke



Build libraries shared or static

I generally build InterViews static. The nrn build will then incorporate all of InterViews into


dlopen X11 after launch

This is most useful for building Mac distributions where XQuartz (X11) may not be installed on the user’s machine and the user does not require InterViews graphics. If XQuartz is subsequently installed, InterViews graphics will suddenly be available.


Remake the X11 dynamic .h files.

Don’t use this. The scripts are very brittle and X11 is very stable. If it is ever necessary to remake the X11 dynamic .h files, I will do so and push them to the respository.

MPI options:


Enable MPI support

Requires an MPI installation, e.g. openmpi or mpich. Note that the Python mpi4py module generally uses openmpi which cannot be mixed with mpich.


Enable dynamic MPI library support

This is mostly useful for binary distibutions where MPI may or may not exist on the target machine.


semicolon (;) separated list of MPI include directories to build against. Default to first found mpi)

Cmake knows about openmpi, mpich, mpt, and msmpi. The dynamic loader for linux tries to load and if that fails, (the latter is good for cray mpi). The system then checks to see if a specific symbol exists in the libmpi… and determines whether to load the for openmpi, mpich, or mpt. To make binary installers good for openmpi and mpich, I use


This option is ignored unless NRN_ENABLE_MPI_DYNAMIC=ON

Python options:


Enable Python interpreter support (default python, fallback to python3, but see PYTHON_EXECUTABLE below)


Enable dynamic Python version support

This is mostly useful for binary distributions where it is unknown which version, if any, of python exists on the target machine.


semicolon (;) separated list of python executables to create interfaces. (default python3)

If the string is empty use the python specified by PYTHON_EXECUTABLE or else the default python. Binary distributions often specify a list of python versions so that if any one of them is available on the target machine, NEURON + Python will be fully functional. Eg. the mac package build script on my machine, nrn/ uses


This option is ignored unless NRN_ENABLE_PYTHON_DYNAMIC=ON


Use provided python binary instead of the one found by CMake. This must be a full path. We generally use

-DPYTHON_EXECUTABLE=`which python3.7`


Enable installation of NEURON Python module.

By default, the neuron module is installed in CMAKE_INSTALL_PREFIX/lib/python.

NRN_MODULE_INSTALL_OPTIONS:STRING=–home=/usr/local options, everything after install

To install in site-packages use an empty string


This option is (or should be) ignored unless NRN_ENABLE_MODULE_INSTALL=ON.


Enable rx3d support

No longer any reason to turn this off as build time is not significantly increased due to compiling cython generated files with -O0 by default.


Optimization level for Cython generated files (non-zero may compile slowly)

It is not clear to me if -O0 has significantly less performance than -O2. Binary distributions are (or should be) built with


CoreNEURON options:


Enable CoreNEURON support

If ON and no argument pointing to an external installation, CoreNEURON will be cloned as a submodule along with all its NMODL submodule dependencies.


Enable CoreNEURON compatibility for MOD files

CoreNEURON does not allow the common NEURON THREADSAFE promotion of GLOBAL variables that appear on the right hand side of assignment statements to become thread specific variables. This option is automatically turned on if NRN_ENABLE_CORENEURON=ON.

There are a large number of cmake arguments specific to a CoreNEURON build that are explained in ???.

Occasionally useful advanced options:

See all the options with ccmake .. in the build folder. They are also in the CMakeCache.txt file. Following is a definitely incomplete list.


C compiler

On the mac, prior to knowing about export SDK_ROOT=$(xcrun -sdk macosx --show-sdk-path) I got into the habit of


to avoid the problem of gcc not being able to find stdio.h when python was compiling inithoc.cpp


C plus plus compiler


Path to a file.

If cmake can’t find readline and you don’t want the nrn internal version, you

can give this hint as to where it is.


Enable unit tests

Clones the submodule catch2 from and after a build using make can run the tests with make test. May also need to pip install pytest. make test is quite terse. To get the same verbose output that is seen with the travis-ci tests, use ctest -VV (executed in the build folder). One can also run individual test files with python3 -m pytest <> or all the test files in that folder with python3 -m pytest. Note: It is helpful to make test first to ensure any mod files needed are available to the tests. If running a test outside the folder where the test is located, it may be necessary to add the folder to PYTHONPATH. Note: The last python mentioned in the -DNRN_PYTHON_DYNAMIC=... (if the semicolon separated list is non-empty and -DNRN_ENABLE_PYTHON_DYNAMIC=ON) is the one used for make test and ctest -VV. Otherwise the value specified by PYTHON_EXECUTABLE is used.


mkdir build
cmake .. -DNRN_ENABLE_TESTS=ON ...
make -j
make test
ctest -VV
cd ../test/pynrn
python3 -m pytest
python3 -m pytest


Enable CMake code formatting

Clones the submodule coding-conventions from Also need to pip install cmake-format=0.6.0 --user. After a build using make can reformat cmake files with make cmake-format See nrn/ for further details. How does one reformat a specific cmake file?

Miscellaneous Rarely used options specific to NEURON:


Enable Observer to be a subclass of DiscreteEvent Can save space but a lot of component destruction may not notify other components that are watching it to no longer use that component. Useful only if one builds a model without needing to eliminate pieces of the model.


Use modern faraday, R, etc. from 2019 nist constants

This option has been removed as a configure/cmake option of version 8.0 and default is to use modern units. At launch time (or import neuron), use of legacy or modern units can be specified with the NRNUNIT_USE_LEGACY=0or1 environment variable. The use of legacy or modern units can be dynamically specified after launch with the h.nrnunit_use_legacy(0or1) function (with no args, returns the current use flag).


Dynamically load nrnmech shared library


Enable use of memacs

Microemacs is a tiny emacs like editor I have been using since the mid-eighties. I might be the only one in the world who uses it now.


Build shared libraries (otherwise static library)

This must be ON if python is launched and imports neuron. If OFF and one wants to use python it will be necessary to launch

nrniv -python


Allow use of Pthreads


Turned on when creating python wheels.


Build binary special

nrnivmodl by default creates shell script called ‘special’ which runs nrniv and specifies the argument -dll /path/to/ or whatever the name is of the shared library created by nrnivmodl. This option forces nrnivmodl to create a binary version of special that can be run, for example, with gdb or valgrind.

It is not often needed as nrniv has a -dll <path/to/> option. Also by default, if the current working directory on launch has a folder named x86_64 (or whatever the CPU happens to be), the nrnmech library in that folder will be automatically loaded.


Use internal Readline library shipped with NEURON

Forces use of the readline code distributed with NEURON even if there is a system supplied readline.