cibuildwheel/docs/faq.md

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It didn't work!

If your wheel didn't compile, check the list below for some debugging tips.

• A mistake in your config. To quickly test your config without doing a git push and waiting for your code to build on CI, you can test the Linux build in a Docker container. On Mac or Linux, with Docker running, try cibuildwheel --platform linux. You'll have to bring your config into the current environment first.

• Missing dependency. You might need to install something on the build machine. You can do this in .travis.yml, appveyor.yml, or .circleci/config.yml, with apt-get, brew or whatever Windows uses :P . Given how the Linux build works, we'll probably have to build something into cibuildwheel. Let's chat about that over in the issues!

• Windows: missing C feature. The Windows C compiler doesn't support C language features invented after 1990, so you'll have to backport your C code to C90. For me, this mostly involved putting my variable declarations at the top of the function like an animal.

• MacOS: calling cibuildwheel from a python3 script and getting a ModuleNotFoundError? Due to a bug in CPython, you'll need to unset the __PYVENV_LAUNCHER__ variable before activating a venv.

Linux builds on Docker

Linux wheels are built in the manylinux1 docker images to provide binary compatible wheels on Linux, according to PEP 513. Because of this, when building with cibuildwheel on Linux, a few things should be taken into account:

• Programs and libraries cannot be installed on the Travis CI Ubuntu host with apt-get, but can be installed inside of the Docker image using yum or manually. The same goes for environment variables that are potentially needed to customize the wheel building. cibuildwheel supports this by providing the CIBW_ENVIRONMENT and CIBW_BEFORE_BUILD options to setup the build environment inside the running Docker image. See below for details on these options.

• The project directory is mounted in the running Docker instance as /project, the output directory for the wheels as /output. In general, this is handled transparently by cibuildwheel. For a more finegrained level of control however, the root of the host file system is mounted as /host, allowing for example to access shared files, caches, etc. on the host file system. Note that this is not available on CircleCI due to their Docker policies.

• Alternative dockers images can be specified with the CIBW_MANYLINUX1_X86_64_IMAGE and CIBW_MANYLINUX1_I686_IMAGE options to allow for a custom, preconfigured build environment for the Linux builds. See options for more details.