Hey folks, especially Rob and Luc. So after a quick change to iotbx/libtbx_config, it turns out there's a way to get a super minimum version of cctbx, without configuring dxtbx, and it takes advantage of existing mechanisms: - python bootstrap.py --builder=cctbx hot update - python modules/cctbx_project/libtbx/auto_build/install_base_packages.py openssl python python_compatibility certifi numpy cython png libsvm pytest pythonextra jinja2 junitxml biopython docutils sphinx pyopengl misc freetype matplotlib pillow gettext glib expat fontconfig render pixman tiff cairo gtk fonts wxpython - mkdir build; cd build - ../base/bin/python ../modules/cctbx_project/libtbx/configure.py cctbx iotbx - make Now, some details as to why this works. First, the cctbx builder in boostrap.py doesn't download cbflib so cbflib is never configured. Next, the base step of bootstrap.py is simply a call to install_base_packages.py with a list of required packages. You can just run it standalone and get the packages you need. Here, I ran "python bootstrap.py --builder=cctbx base", killed it after I saw the list of packages it was going to install, then ran install_base_packages manually after removing hdf5 and lz4 (which depends on hdf5) from the list. One could imagine removing other packages depending on your use case. With that, I could run configure.py directly. I can't use cctbx by itself as the cctbx/maptbx/SConscript file has a dependency on iotbx, but configuring cctbx and iotbx together seems to work. The key trick was to make iotbx only depend on dxtbx if dxtbx is explicitly configured. I used a keyword in libtbx_configure added by Luc a bit ago: optional_modules_only_if_explicit_request. I committed that change just now. Outstanding questions: 1. Is there interest in making this a builder? It would be straightforward to add a builder named cctbx_minimal which would just do the above steps 2. Is there further need for making cbflib and hdf5 optional in dxtbx? I purport there is not as the above procedure seems to satisfy the use case, but I can be persuaded otherwise. Thanks, -Aaron