Q:

Create conda environment: "Found conflicts!" when solving environment and "Finding shortest conflict path" running forever

I was provided with an environment.ubuntu.yml file to be able to create a conda environment. However, running conda create env --file environment.ubuntu.yml I get the following output:
conda env create --file environment.ubuntu.yml
Collecting package metadata (repodata.json): done
Solving environment: - 
Found conflicts! Looking for incompatible packages.
This can take several minutes.  Press CTRL-C to abort.
Examining fontconfig:   5%|▉                 | 10/202 [00:00<00:00, 5393.91it/ ]
Comparing specs that have this dependency:   0%|         | 0/12 [00:00<?, ?it/s]
Finding shortest confli|  path for fontconfig==2.13.1=he4413a7_1000:  12%|▏| 1/8
Finding shortest conflict path for fontconfig==2.13.1=he4413a7_1000:  25%|▎| 2/8
Finding shortest conflict pa/  for fontconfig[version='>=2.13.0,<3.0a0']:  25%|
Finding shortest conflict path for fontconfig[version='>=2.13.0,<3.0a0']:  38%|
Finding shortest conf- ct path for fontconfig[version='>=2.11.1']:  38%|▍| 3/8 [
Finding shortest conflict path for fontconfig[version='>=2.11.1']:  50%|▌| 4/8 [
Finding shortest conflict pa|  for fontconfig[version='>=2.12.4,<3.0a0']:  50%|
...

The Finding shortest conflict path goes on for a long time - apparently it is trying to resolve some dependency issues. Running for 2 hours it is not clear if it will ever stop.
My question is: what is happening here and can I somehow manually speed up this process, e.g. by removing unnecessary dependencies? Since I did not create the environment I don't know which are actually necessary.
The reason why I'm curious is because it is checking conflict paths like fontconfig[version='>=2.12.6,<3.0a0'] when the one in dependencies is 2.13.1 and I have installed it through 2.13.1
Please find below the .yml file for reference.
name: cea
channels:
  - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/free
  - dlr-sc
  - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/main
  - conda-forge
  - conda-forge/label/gcc7
  - defaults
dependencies:
  - attrs=19.1.0=py_0
  - backports=1.0=py_2
  - backports.functools_lru_cache=1.5=py_1
  - backports_abc=0.5=py_1
  - boost-cpp=1.68.0=h11c811c_1000
  - bzip2=1.0.6=h14c3975_1002
  - ca-certificates=2019.3.9=hecc5488_0
  - cairo=1.14.12=h80bd089_1005
  - certifi=2019.3.9=py27_0
  - click=7.0=py_0
  - click-plugins=1.0.4=py_0
  - cligj=0.5.0=py_0
  - curl=7.64.1=hf8cf82a_0
  - cycler=0.10.0=py_1
  - descartes=1.1.0=py_2
  - enum34=1.1.6=py27_1001
  - expat=2.2.5=hf484d3e_1002
  - fiona=1.8.6=py27hf242f0b_2
  - fontconfig=2.13.1=he4413a7_1000
  - freetype=2.10.0=he983fc9_0
  - freexl=1.0.5=h14c3975_1002
  - functools32=3.2.3.2=py_3
  - futures=3.2.0=py27_1000
  - gdal=2.4.1=py27h5f563d9_8
  - geopandas=0.4.1=py_1
  - geos=3.7.1=hf484d3e_1000
  - geotiff=1.4.3=h1105359_1000
  - gettext=0.19.8.1=hc5be6a0_1002
  - giflib=5.1.7=h516909a_1
  - glib=2.56.2=had28632_1001
  - hdf4=4.2.13=h9a582f1_1002
  - hdf5=1.10.4=nompi_h3c11f04_1106
  - icu=58.2=hf484d3e_1000
  - jpeg=9c=h14c3975_1001
  - json-c=0.13.1=h14c3975_1001
  - kealib=1.4.10=h1978553_1003
  - kiwisolver=1.0.1=py27h6bb024c_1002
  - krb5=1.16.3=h05b26f9_1001
  - libblas=3.8.0=4_openblas
  - libcblas=3.8.0=4_openblas
  - libcurl=7.64.1=hda55be3_0
  - libdap4=3.19.1=hd48c02d_1000
  - libedit=3.1.20170329=hf8c457e_1001
  - libffi=3.2.1=he1b5a44_1006
  - libgdal=2.4.1=heae24aa_8
  - libiconv=1.15=h516909a_1005
  - libkml=1.3.0=h328b03d_1009
  - liblapack=3.8.0=4_openblas
  - libnetcdf=4.6.2=hbdf4f91_1001
  - libpng=1.6.36=h84994c4_1000
  - libpq=11.2=h4770945_0
  - libspatialindex=1.9.0=he1b5a44_0
  - libspatialite=4.3.0a=hb5ec416_1026
  - libssh2=1.8.2=h22169c7_2
  - libtiff=4.0.10=h648cc4a_1001
  - libuuid=2.32.1=h14c3975_1000
  - libxcb=1.13=h14c3975_1002
  - libxml2=2.9.8=h143f9aa_1005
  - mapclassify=1.0.1=py27_1
  - matplotlib=2.2.3=py27h8a2030e_1
  - matplotlib-base=2.2.3=py27h60b886d_1
  - munch=2.3.2=py_0
  - ncurses=6.1=hf484d3e_1002
  - numpy=1.16.2=py27h8b7e671_1
  - openblas=0.3.5=h9ac9557_1001
  - openjpeg=2.3.0=hf38bd82_1003
  - openssl=1.1.1b=h14c3975_1
  - pandas=0.24.2=py27hf484d3e_0
  - pip=19.0.3=py27_0
  - pixman=0.34.0=h14c3975_1003
  - poppler=0.67.0=h2fc8fa2_1002
  - poppler-data=0.4.9=1
  - postgresql=11.2=h61314c7_0
  - proj4=5.2.0=h14c3975_1001
  - pthread-stubs=0.4=h14c3975_1001
  - pyparsing=2.3.1=py_0
  - pyproj=1.9.6=py27hc0953d3_1000
  - pyqt=5.6.0=py27h13b7fb3_1008
  - python=2.7.15=h721da81_1008
  - python-dateutil=2.8.0=py_0
  - pytz=2018.9=py_0
  - readline=7.0=hf8c457e_1001
  - rtree=0.8.3=py27h666c49c_1002
  - scipy=1.2.1=py27h09a28d5_1
  - setuptools=40.8.0=py27_0
  - shapely=1.6.4=py27h2afed24_1003
  - singledispatch=3.4.0.3=py27_1000
  - sip=4.18.1=py27hf484d3e_1000
  - six=1.12.0=py27_1000
  - sqlite=3.26.0=h67949de_1001
  - subprocess32=3.5.3=py27h14c3975_0
  - tbb=2019.5=hc9558a2_0
  - tk=8.6.9=h84994c4_1001
  - tornado=5.1.1=py27h14c3975_1000
  - tzcode=2018g=h14c3975_1001
  - wheel=0.33.1=py27_0
  - xerces-c=3.2.2=hac72e42_1001
  - xorg-kbproto=1.0.7=h14c3975_1002
  - xorg-libice=1.0.9=h516909a_1004
  - xorg-libsm=1.2.3=h84519dc_1000
  - xorg-libx11=1.6.7=h14c3975_1000
  - xorg-libxau=1.0.9=h14c3975_0
  - xorg-libxdmcp=1.1.3=h516909a_0
  - xorg-libxext=1.3.4=h516909a_0
  - xorg-libxrender=0.9.10=h516909a_1002
  - xorg-renderproto=0.11.1=h14c3975_1002
  - xorg-xextproto=7.3.0=h14c3975_1002
  - xorg-xproto=7.0.31=h14c3975_1007
  - xz=5.2.4=h14c3975_1001
  - zlib=1.2.11=h14c3975_1004
  - freeimageplus=3.18.0=hf484d3e_2
  - gl2ps=1.3.8=h14c3975_4
  - oce=0.17.2=h6bb024c_10
  - pythonocc-core=0.17=py27_1
  - mkl=2017.0.3=0
  - mkl-service=1.1.2=py27_3
  - dbus=1.13.2=h714fa37_1
  - gst-plugins-base=1.14.0=hbbd80ab_1
  - gstreamer=1.14.0=hb453b48_1
  - libgcc-ng=8.2.0=hdf63c60_1
  - libgfortran-ng=7.3.0=hdf63c60_0
  - libstdcxx-ng=8.2.0=hdf63c60_1
  - pcre=8.43=he6710b0_0
  - qt=5.6.3=h8bf5577_3
  - pip:
    - alabaster==0.7.12
    - babel==2.6.0
    - backports.shutil-get-terminal-size==1.0.0
    - bleach==3.1.0
    - chardet==3.0.4
    - cloudpickle==0.8.1
    - configparser==3.7.4
    - cvxopt==1.2.3
    - decorator==4.4.0
    - defusedxml==0.5.0
    - docutils==0.14
    - doit==0.29.0
    - entrypoints==0.3
    - ephem==3.7.6.0
    - funcsigs==1.0.2
    - h5py==2.9.0
    - idna==2.8
    - imagesize==1.1.0
    - importlib-resources==1.0.2
    - ipaddress==1.0.22
    - ipykernel==4.10.0
    - ipython==5.8.0
    - ipython-genutils==0.2.0
    - ipywidgets==7.4.2
    - jinja2==2.10
    - joblib==0.12.5
    - jsonschema==3.0.1
    - jupyter==1.0.0
    - jupyter-client==5.2.4
    - jupyter-console==5.2.0
    - jupyter-core==4.4.0
    - llvmlite==0.28.0
    - lxml==4.3.3
    - markupsafe==1.1.1
    - mistune==0.8.4
    - mock==2.0.0
    - nbconvert==5.4.1
    - nbformat==4.4.0
    - networkx==2.2
    - notebook==5.7.8
    - numba==0.43.1
    - packaging==19.0
    - pandocfilters==1.4.2
    - pathlib2==2.3.3
    - patsy==0.5.1
    - pbr==5.1.3
    - pexpect==4.6.0
    - pickleshare==0.7.5
    - pkginfo==1.5.0.1
    - plotly==3.7.1
    - prometheus-client==0.6.0
    - prompt-toolkit==1.0.15
    - ptyprocess==0.6.0
    - py4design==0.27
    - pycollada==0.6
    - pygments==2.3.1
    - pyinotify==0.9.6
    - pymc3==3.6
    - pymf==0.1.9
    - pyrsistent==0.14.11
    - pysal==1.14.4.post2
    - pyshp==2.1.0
    - pyyaml==5.1
    - pyzmq==18.0.1
    - qtconsole==4.4.3
    - readme-renderer==24.0
    - requests==2.21.0
    - requests-toolbelt==0.9.1
    - retrying==1.3.3
    - salib==1.2
    - scandir==1.10.0
    - scikit-learn==0.20.3
    - seaborn==0.9.0
    - send2trash==1.5.0
    - simplegeneric==0.8.1
    - snowballstemmer==1.2.1
    - sphinx==1.8.5
    - sphinxcontrib-websupport==1.1.0
    - terminado==0.8.2
    - testpath==0.4.2
    - theano==1.0.4
    - timezonefinder==4.0.1
    - tqdm==4.31.1
    - traitlets==4.3.2
    - twine==1.13.0
    - typing==3.6.6
    - urllib3==1.24.1
    - utm==0.4.2
    - wcwidth==0.1.7
    - webencodings==0.5.1
    - widgetsnbextension==3.4.2
    - xlrd==1.2.0
    - xlwt==1.3.0
    - deap==1.3.0

A:

This error and the subsequent behaviour is very likely coming from the Anaconda bug which from time to time causes inconsistencies in the local environment. As of Jan 26th, 2020 the bug was not yet resolved.
For me the same problem manifests profoundly on Mac.

A:

In general, the answer to this question is that you should create your .yml from hand by scratch, with only the required channels and constraints. You should relax the version constraints so that they only look like 1.19 instead of 1.19.10
However, despite following this advice, I have almost exactly your problem right now. It spent many hours on fontconfig and I left it overnight before giving up. My spec is pretty simple:
channels:
  - conda-forge
  - usgs-astrogeology
  - defaults
dependencies:
  - python=3.6
  - isis3
  - gdal=2.3

I'll edit this when I figure it out.
EDIT: This problem is under discussion here (specific to the software I was trying to set up, probably not helpful for others) https://github.com/USGS-Astrogeology/ISIS3/issues/3570

