# How to build PyLith and link it to external dynamic libraries in macOS?

**URL:** <https://community.geodynamics.org/t/how-to-build-pylith-and-link-it-to-external-dynamic-libraries-in-macos/780>\
**Category:** PyLith\
**Tags:** installation\
**Created:** [August 26, 2019, 7:57pm UTC](https://community.geodynamics.org/t/how-to-build-pylith-and-link-it-to-external-dynamic-libraries-in-macos/780 "2019-08-26T19:57:11Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![josimar](https://avatars.discourse-cdn.com/v4/letter/j/cab0a1/32.png) [@josimar](https://community.geodynamics.org/u/josimar)\
**Post date:** [August 26, 2019, 7:57pm UTC](https://community.geodynamics.org/t/how-to-build-pylith-and-link-it-to-external-dynamic-libraries-in-macos/780/1 "2019-08-26T19:57:11Z")

</div>

Hi Brad,

I am trying to build Pylith from source and link it to an external dynamic library but I am facing issues.

For example, in the code below I link a simple C++ code to my dynamic library called DataLib.dylib. The executable only works if I use `install_name_tool` to change the relative path of the executable file (`@rpath`) to the absolute path of the library.

```
export DYLD_LIBRARY_PATH='/home/bin/maci64:/home/sys/os/maci64':$DYLD_LIBRARY_PATH

g++ -o myCodeCxx myCodeCxx.cpp -v -std=c++11 -I/home/extern/include -L/home/extern/bin/maci64 -lDataLib 

# myCodeCxx will only work if I change from the relative path to the absolute:
install_name_tool -change @rpath/libMatlabEngine.dylib /home/extern/bin/maci64/DataLib.dylib myCodeCxx`

```

When building Pylith, I modified the main Makefile that is created right after calling `./configure` to include also `-I/home/extern/include`, `-L/home/extern/bin/maci64` and `-lDataLib`.

The whole building process finished without any errors. However, when I try to run pylith I get the following error message, which indicates that the Pylith executable did not find my dynamic library:

```
Traceback (most recent call last):
  File "/home/Install/pylith/bin/pylith", line 25, in <module>
    from pylith.apps.PyLithApp import PyLithApp
  File "/home/Install/pylith/lib/python2.7/site-packages/pylith/apps/PyLithApp.py", line 23, in <module>
    from PetscApplication import PetscApplication
  File "/home/Install/pylith/lib/python2.7/site-packages/pylith/apps/PetscApplication.py", line 27, in <module>
    class PetscApplication(Application):
  File "/home/Install/pylith/lib/python2.7/site-packages/pylith/apps/PetscApplication.py", line 41, in PetscApplication
    from pylith.utils.PetscManager import PetscManager
  File "/home/Install/pylith/lib/python2.7/site-packages/pylith/utils/PetscManager.py", line 29, in <module>
    import pylith.utils.petsc as petsc
  File "/home/Install/pylith/lib/python2.7/site-packages/pylith/utils/petsc.py", line 28, in <module>
    _petsc = swig_import_helper()
  File "/home/Install/pylith/lib/python2.7/site-packages/pylith/utils/petsc.py", line 24, in swig_import_helper
    _mod = imp.load_module('_petsc', fp, pathname, description)
ImportError: dlopen(/home/Install/pylith/lib/python2.7/site-packages/pylith/utils/_petscmodule.so, 2): Symbol not found: _cpp_engine_cancel_feval_with_completion
  Referenced from: /home/Install/pylith/lib/libpylith.0.dylib
  Expected in: flat namespace
 in /home/Install/pylith/lib/libpylith.0.dylib

```

The error message above seems in agreement with what I find with my simple C++ code if I don’t run the `install_name_tool` on the main executable file. Note that I am setting the `DYLD_LIBRARY_PATH` variable to the correct locations of my library, like I did with my simple C++ code.

My questions are:

1. Could you please let me know how do I find the main pylith executable file so that I can try using the `install_name_tool` ? when I try `which pylith` I get a path to file that gives an error to `install_name_tool`.
2. Would you have any suggestions to fix this issue ? Perhaps a way to include the `install_name_tool` on the main Makefile ?

Note the following: I repeated the same procedure on a Linux computer and everything went fine and I was able to link it to my external library, which unfortunately does not happen on macOS system.

Thanks in advance for you help.

---

<div class="post-metadata">

**Author:** ![baagaard](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/baagaard/32/615_2.png) [@baagaard](https://community.geodynamics.org/u/baagaard)\
**Post date:** [August 28, 2019, 7:06pm UTC](https://community.geodynamics.org/t/how-to-build-pylith-and-link-it-to-external-dynamic-libraries-in-macos/780/2 "2019-08-28T19:06:40Z")

</div>

Use `otool -L LIBRARY.dylib` to see how the paths to other dynamic libraries are being resolved. I believe `DYLD_LIBRARY_PATH` is no longer supported on under Mac OS X.

The PyLith executable is just a Python script, so you can’t run `install_name_tool` on it. The libraries and Python modules are what have paths to other dynamic libraries. You shouldn’t need to use `install_name_tool` unless you move libraries. Everything should be handled properly with the proper link lines. You can adjust the local `Makefile.am` for all of the libraries and modules making use of the external library.