title: pynestkernel ImportError: libmpi_cxx.so.20: cannot open shared object file: No such file or directory
body: <p>When installing NEST 2.18 with:</p>
  <pre><code>cmake \
    -Dwith-mpi=/usr/lib/x86_64-linux-gnu/openmpi \
    -Dwith-python=3 \
    -DPYTHON_EXECUTABLE=/home/robin/.pyenv/versions/3.8.6/bin/python \
    -DPYTHON_LIBRARY=/home/robin/.pyenv/versions/3.8.6/lib/libpython3.8.so \
    -DPYTHON_INCLUDE_DIR=/home/robin/.pyenv/versions/3.8.6/include/python3.8/ \
    -DCMAKE_INSTALL_PREFIX=/home/robin/nest-install \
    ..
  </code></pre>
  <p>It seems that NEST 2.18 tries to look for <code>libmpi_cxx.so.20</code> even though it doesn't exist and isn't part of the installed mpi lib</p>
  <pre><code>$ ldd nest-install/lib/python3.8/site-packages/nest/pynestkernel.so 
      linux-vdso.so.1 (0x00007fff3bb37000)
      libpython3.8.so.1.0 =&gt; /home/robin/.pyenv/versions/3.8.6/lib/libpython3.8.so.1.0 (0x00007feaa1401000)
      libnest.so =&gt; /nest/2.18/lib/libnest.so (0x00007feaa11c1000)
      libmodels.so =&gt; /nest/2.18/lib/libmodels.so (0x00007feaa0930000)
      libtopology.so =&gt; /nest/2.18/lib/libtopology.so (0x00007feaa0691000)
      libnestkernel.so =&gt; /nest/2.18/lib/libnestkernel.so (0x00007feaa0335000)
      librandom.so =&gt; /nest/2.18/lib/librandom.so (0x00007feaa00e9000)
      libsli.so =&gt; /nest/2.18/lib/libsli.so (0x00007fea9fd9a000)
      libstdc++.so.6 =&gt; /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fea9fba1000)
      libgcc_s.so.1 =&gt; /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fea9fb86000)
      libc.so.6 =&gt; /lib/x86_64-linux-gnu/libc.so.6 (0x00007fea9f994000)
      libpthread.so.0 =&gt; /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fea9f971000)
      libdl.so.2 =&gt; /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fea9f969000)
      libutil.so.1 =&gt; /lib/x86_64-linux-gnu/libutil.so.1 (0x00007fea9f964000)
      libm.so.6 =&gt; /lib/x86_64-linux-gnu/libm.so.6 (0x00007fea9f815000)
      libprecise.so =&gt; /nest/2.18/lib/libprecise.so (0x00007fea9f592000)
      libltdl.so.7 =&gt; /usr/lib/x86_64-linux-gnu/libltdl.so.7 (0x00007fea9f587000)
      libmpi_cxx.so.20 =&gt; /usr/lib/x86_64-linux-gnu/openmpi/lib/libmpi_cxx.so.20 (0x00007fea9f567000)
      libmpi.so.20 =&gt; not found
      libnestutil.so =&gt; /nest/2.18/lib/libnestutil.so (0x00007fea9f363000)
      libgsl.so.23 =&gt; /usr/lib/x86_64-linux-gnu/libgsl.so.23 (0x00007fea9f0e7000)
      libgslcblas.so.0 =&gt; /usr/lib/x86_64-linux-gnu/libgslcblas.so.0 (0x00007fea9f0a5000)
      libgomp.so.1 =&gt; /usr/lib/x86_64-linux-gnu/libgomp.so.1 (0x00007fea9f063000)
      /lib64/ld-linux-x86-64.so.2 (0x00007feaa180a000)
      libmpi.so.20 =&gt; not found
      libmpi.so.20 =&gt; not found
      libmpi.so.20 =&gt; not found
      libmpi.so.20 =&gt; not found
      libmpi.so.40 =&gt; /usr/local/lib/libmpi.so.40 (0x00007fea9ed39000)
      libopen-rte.so.40 =&gt; /usr/local/lib/libopen-rte.so.40 (0x00007fea9ea83000)
      libopen-pal.so.40 =&gt; /usr/local/lib/libopen-pal.so.40 (0x00007fea9e76b000)
      librt.so.1 =&gt; /lib/x86_64-linux-gnu/librt.so.1 (0x00007fea9e760000)
      libz.so.1 =&gt; /lib/x86_64-linux-gnu/libz.so.1 (0x00007fea9e744000)
  </code></pre>
  <p>I've tried to change all of the cmake variables using <code>ccmake</code> but I can't get it to link to <code>libmpi_cxx.so.40</code>.</p>
  <p>Even without MPI support it includes this link, seems like a bug?</p>
  <pre><code>robin@robin-ZenBook-UX533FN:~$ ldd nest-install/lib/python3.8/site-packages/nest/pynestkernel.so 
      linux-vdso.so.1 (0x00007ffe63518000)
      libpython3.8.so.1.0 =&gt; /home/robin/.pyenv/versions/3.8.6/lib/libpython3.8.so.1.0 (0x00007fa1e3c37000)
      libnest.so =&gt; /nest/2.18/lib/libnest.so (0x00007fa1e39f7000)
      libmodels.so =&gt; /nest/2.18/lib/libmodels.so (0x00007fa1e3166000)
      libtopology.so =&gt; /nest/2.18/lib/libtopology.so (0x00007fa1e2ec7000)
      libnestkernel.so =&gt; /nest/2.18/lib/libnestkernel.so (0x00007fa1e2b6b000)
      librandom.so =&gt; /nest/2.18/lib/librandom.so (0x00007fa1e291f000)
      libsli.so =&gt; /nest/2.18/lib/libsli.so (0x00007fa1e25d0000)
      libstdc++.so.6 =&gt; /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fa1e23d7000)
      libgcc_s.so.1 =&gt; /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fa1e23bc000)
      libc.so.6 =&gt; /lib/x86_64-linux-gnu/libc.so.6 (0x00007fa1e21ca000)
      libpthread.so.0 =&gt; /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fa1e21a7000)
      libdl.so.2 =&gt; /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fa1e219f000)
      libutil.so.1 =&gt; /lib/x86_64-linux-gnu/libutil.so.1 (0x00007fa1e219a000)
      libm.so.6 =&gt; /lib/x86_64-linux-gnu/libm.so.6 (0x00007fa1e204b000)
      libprecise.so =&gt; /nest/2.18/lib/libprecise.so (0x00007fa1e1dc8000)
      libltdl.so.7 =&gt; /usr/lib/x86_64-linux-gnu/libltdl.so.7 (0x00007fa1e1dbd000)
      libmpi_cxx.so.20 =&gt; not found
      libmpi.so.20 =&gt; not found
      libnestutil.so =&gt; /nest/2.18/lib/libnestutil.so (0x00007fa1e1bb7000)
      libgsl.so.23 =&gt; /usr/lib/x86_64-linux-gnu/libgsl.so.23 (0x00007fa1e193b000)
      libgslcblas.so.0 =&gt; /usr/lib/x86_64-linux-gnu/libgslcblas.so.0 (0x00007fa1e18f9000)
      libgomp.so.1 =&gt; /usr/lib/x86_64-linux-gnu/libgomp.so.1 (0x00007fa1e18b7000)
      /lib64/ld-linux-x86-64.so.2 (0x00007fa1e4040000)
      libmpi_cxx.so.20 =&gt; not found
      libmpi.so.20 =&gt; not found
      libmpi_cxx.so.20 =&gt; not found
      libmpi.so.20 =&gt; not found
      libmpi_cxx.so.20 =&gt; not found
      libmpi.so.20 =&gt; not found
      libmpi_cxx.so.20 =&gt; not found
      libmpi.so.20 =&gt; not found
  </code></pre>
  <p>The full error when importing it is:</p>
  <pre><code>&gt;&gt;&gt; import nest
  Traceback (most recent call last):
    File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;
    File &quot;/home/robin/nest-install/lib/python3.8/site-packages/nest/__init__.py&quot;, line 26, in &lt;module&gt;
      from . import ll_api      # noqa
    File &quot;/home/robin/nest-install/lib/python3.8/site-packages/nest/ll_api.py&quot;, line 72, in &lt;module&gt;
      from . import pynestkernel as kernel      # noqa
  ImportError: libmpi_cxx.so.20: cannot open shared object file: No such file or directory
  </code></pre>