anchor.diff:  #
   # Note: Spack claims that Python 3 works, but using python3 here fails later
   # with "/usr/bin/env: 'python': No such file or directory".
  -RUN apt-get install -y \
  +RUN yum update -y && \
  +    yum install install -y \
  +    curl \
  +    gcc \
  +    gcc-c++ \
  +    git \
  +    gnupg2-smime \
       python \
  -    gcc \
  -    make \
  -    git \
  -    curl
  +    make
   
   # Packages needed to install Charliecloud with Spack. These are in Spack's
   # Docker example [2] but are not documented as prerequisites [1].
  -RUN apt-get install -y \
  -    g++ \
  -    unzip
  +RUN yum install -y \
  +    bzip2 \
  +    file \
  +    patch \
  +    unzip \
  +    which
   
   # Certain Spack packages (e.g., tar) puke if they detect themselves being
   # configured as UID 0. This is the override. See issue #540 and [2].
  
positive.code: # Test: Some basic commands.
  RUN which spack
  RUN spack --version
  RUN spack compiler list
  RUN spack compiler list --scope=system
  RUN spack compiler list --scope=user
  RUN spack compilers
  RUN spack spec netcdf
  
  # Test: Install Charliecloud.
  RUN spack spec charliecloud+builder
  RUN spack install charliecloud+builder
  
  # Test: Run Spack test suite. Distro package dependencies discovered by trial
  # and error.
  #
  # FIXME: Commented out because the suite fails. Last time I tried, 6 tests
  # failed and 1 "xfailed".
  #RUN apt-get install -y \
  #    python-pkg-resources
  #RUN spack test
  
  # Clean up.
  RUN spack clean --all
  
negative.code: # ch-test-scope: full
  FROM centos:7
  
  # Note: Spack is a bit of an odd duck testing wise. Because it's a package
  # manager, the key tests we want are to install stuff (this includes the Spack
  