Building the Bootloader

PyInstaller comes with pre-compiled bootloaders for some platforms in the bootloader folder of the distribution folder. When there is no pre-compiled bootloader for the current platform (operating-system and word-size), the pip setup will attempt to build one.

If there is no precompiled bootloader for your platform, or if you want to modify the bootloader source, you need to build the bootloader. To do this,

  • Download and install Python, which is required for running waf,

  • git clone or download the source from our GitHub repository,

  • cd into the folder where you cloned or unpacked the source to,

  • cd bootloader, and

  • make the bootloader with: python ./waf all,

  • test the build by ref:running (parts of) the test-suite <running-the-test-suite>.

This will produce the bootloader executables for your current platform (of course, for Windows these files will have the .exe extension):

  • ../PyInstaller/bootloader/OS_ARCH/run,

  • ../PyInstaller/bootloader/OS_ARCH/run_d,

  • ../PyInstaller/bootloader/OS_ARCH/runw (macOS and Windows only), and

  • ../PyInstaller/bootloader/OS_ARCH/runw_d (macOS and Windows only).

The bootloaders architecture defaults to the machine’s one, but can be changed using the --target-arch option – given the appropriate compiler and development files are installed. E.g. to build a 32-bit bootloader on a 64-bit machine, run:

python ./waf all --target-arch=32bit

If this reports an error, read the detailed notes that follow, then ask for technical help.

By setting the environment variable PYINSTALLER_COMPILE_BOOTLOADER the pip setup will attempt to build the bootloader for your platform, even if it is already present. Doing so would execute the command python ./waf configure all upon installation. You can also pass additional arguments to the build process by setting the PYINSTALLER_BOOTLOADER_WAF_ARGS environment variable.

Supported platforms are

  • GNU/Linux (using gcc)

  • Windows (using Visual C++ (VS2015 or later) or MinGW’s gcc)

  • Mac OX X (using clang)

Contributed platforms are

  • AIX (using gcc or xlc)

  • HP-UX (using gcc or xlc)

  • Solaris

For more information about cross-building please read on and mind the section about the virtual machines provided in the Vagrantfile.

Building for GNU/Linux

Development Tools

For building the bootloader you’ll need a development environment. You can run the following to install everything required:

  • On Debian- or Ubuntu-like systems:

    sudo apt-get install build-essential zlib1g-dev
  • On Fedora, RedHat and derivates:

    sudo yum groupinstall "Development Tools"
    sudo yum install zlib-devel
  • For other Distributions please consult the distributions documentation.

Now you can build the bootloader as shown above.

Alternatively you may want to use the linux64 build-guest provided by the Vagrantfile (see below).

Cross Building for Different Architectures

Bootloaders can be built for other architectures such as ARM or MIPS using Docker. The Dockerfile contains the instructions on how to do this. Open it in some flavour of text previewer to see them:

less bootloader/Dockerfile

Building for macOS

On macOS please install Xcode, Apple’s suite of tools for developing software for macOS. Instead of installing the full Xcode package, you can also install and use Command Line Tools for Xcode. Installing either will provide the clang compiler.

If the toolchain supports universal2 binaries, the 64-bit bootloaders are by default built as universal2 fat binaries that support both x86_64 and arm64 architectures. This requires a recent version of Xcode (12.2 or later). On older toolchains that lack support for universal2 binaries, a single-arch x86_64 thin bootloader is built. This behavior can be controlled by passing --universal2 or --no-universal2 flags to the waf build command. Attempting to use --universal2 flag and a toolchain that lacks support for universal2 binaries will result in configuration error.

The --no-universal2 flag leaves the target architecture unspecified letting the resultant executable’s architecture be the C compiler’s default (which is almost certainly the architecture of the build machine). Should you want to build a thin executable of either architecture, use the --no-universal2 flag and then optionally override the compiler, adding the -arch flag, via the CC environment variable.

Build a thin, native executable:

python waf --no-universal2 all

Build a thin, x86_64 executable (regardless of the build machine’s architecture):

CC='clang -arch x86_64' python waf --no-universal2  all

Build a thin, arm64 executable (regardless of the build machine’s architecture):

CC='clang -arch arm64' python waf --no-universal2 all

By default, the build script targets macOS 10.13, which can be overridden by exporting the MACOSX_DEPLOYMENT_TARGET environment variable.

Cross-Building for macOS

For cross-compiling for macOS you need the Clang/LLVM compiler, the cctools (ld, lipo, …), and the OSX SDK. Clang/LLVM is a cross compiler by default and is available on nearly every GNU/Linux distribution, so you just need a proper port of the cctools and the macOS SDK.

This is easy to get and needs to be done only once and the result can be transferred to you build-system. The build-system can then be a normal (somewhat current) GNU/Linux system. 1


Please keep in mind that to avoid problems, the system you are using for the preparation steps should have the same architecture (and possible the same GNU/Linux distribution version) as the build-system.

Preparation: Get SDK and Build-tools

For preparing the SDK and building the cctools, we use the very helpful scripts from the OS X Cross toolchain. If you are interested in the details, and what other features OS X Cross offers, please refer to its homepage.

To save you reading the OSXCross’ documentation, we prepared a virtual box definition that performs all required steps. If you are interested in the precise commands, please refer to packages_osxcross_debianoid, prepare_osxcross_debianiod, and build_osxcross in the Vagrantfile.

Please proceed as follows:

  1. Download Command Line Tools for Xcode 12.2 or later. You will need an Apple ID to search and download the files; if you do not have one already, you can register it for free.

    Please make sure that you are complying to the license of the respective package.

  2. Save the downloaded .dmg file to bootloader/_sdks/osx/Xcode_tools.dmg.

  3. Use the Vagrantfile to automatically build the SDK and tools:

    vagrant up build-osxcross && vagrant halt build-osxcross

    This should create the file bootloader/_sdks/osx/osxcross.tar.xz, which will then be installed on the build-system.

    If for some reason this fails, try running vagrant provision build-osxcross.

  4. This virtual machine is no longer used, you may now want to discard it using vagrant destroy build-osxcross.

Building the Bootloader

Again, simply use the Vagrantfile to automatically build the macOS bootloaders:

export TARGET=OSX  # make the Vagrantfile build for macOS
vagrant up linux64 && vagrant halt linux

This should create the bootloaders in * ../PyInstaller/bootloader/Darwin-*/.

If for some reason this fails, try running vagrant provision linux64.

  1. This virtual machine is no longer used, you may now want to discard it using:

    vagrant destroy build-osxcross
  2. If you are finished with the macOS bootloaders, unset TARGET again:

    unset TARGET

If you don’t want to use the build-guest provided by the Vagrant file, perform the following steps (see build_bootloader_target_osx in the Vagrantfile):

mkdir -p ~/osxcross
tar -C ~/osxcross --xz -xf /vagrant/sdks/osx/osxcross.tar.xz
python ./waf all CC=x86_64-apple-darwin15-clang
python ./waf all CC=i386-apple-darwin15-clang

Building for Windows

The pre-compiled bootloader coming with PyInstaller are self-contained static executable that imposes no restrictions on the version of Python being used.

When building the bootloader yourself, you have to carefully choose between three options:

  1. Using the Visual Studio C++ compiler.

    This allows creating self-contained static executables, which can be used for all versions of Python. This is why the bootloaders delivered with PyInstaller are build using Visual Studio C++ compiler.

    Visual Studio 2015 or later is required.

  2. Using the MinGW-w64 suite.

    This allows to create smaller, dynamically linked executables, but requires to use the same level of Visual Studio 2 as was used to compile Python. So this bootloader will be tied to a specific version of Python.

    The reason for this is, that unlike Unix-like systems, Windows doesn’t supply a system standard C library, leaving this to the compiler. But Mingw-w64 doesn’t have a standard C library. Instead it links against msvcrt.dll, which happens to exist on many Windows installations – but is not guaranteed to exist.


This description seems to be technically incorrect. I ought to depend on the C++ run-time library. If you know details, please open an issue.

  1. Using cygwin and MinGW.

    This will create executables for cygwin, not for ‘plain’ Windows.

In all cases you may want

  • to set the path to include python, e.g. set PATH=%PATH%;c:\python35,

  • to peek into the Vagrantfile or ../appveyor.yml to learn how we are building.

You can also build the bootloaders for cygwin.

Build using Visual Studio C++

  • With our wscript file, you don’t need to run vcvarsall.bat to ’switch’ the environment between VC++ installations and target architecture. The actual version of C++ does not matter and the target architecture is selected by using the --target-arch= option.

  • If you are not using Visual Studio for other work, installing only the standalone C++ build-tools might be the best option as it avoids bloating your system with stuff you don’t need (and saves a lot if installation time).


    We recommend installing the build-tools software using the chocolatey package manager. While at a first glance it looks like overdose, this is the easiest way to install the C++ build-tools. It comes down to two lines in an administrative powershell:

    … one-line-install as written on the chocolatey homepage
    choco install -y python3 visualstudio2019-workload-vctools
  • Useful Links:

After installing the C++ build-tool you can build the bootloader as shown above.

Build using MinGW-w64

Please be aware of the restrictions mentioned above.

If Visual Studio is not convenient, you can download and install the MinGW distribution from one of the following locations:

  • MinGW-w64 required, uses gcc 4.4 and up.

  • TDM-GCC - MinGW (not used) and MinGW-w64 installers

Note: Please mind that using cygwin’s python or MinGW when running ./waf will create executables for cygwin, not for Windows.

On Windows, when using MinGW-w64, add PATH_TO_MINGWbin to your system PATH. variable. Before building the bootloader run for example:

set PATH=C:\MinGW\bin;%PATH%

Now you can build the bootloader as shown above. If you have installed both Visual C++ and MinGW, you might need to add run python ./waf --gcc all.

Build using cygwin and MinGW

Please be aware that this will create executables for cygwin, not for ‘plain’ Windows.

Use cygwin’s setup.exe to install python and mingw.

Now you can build the bootloader as shown above.

Building for AIX

  • By default AIX builds 32-bit executables.

  • For 64-bit executables set the environment variable OBJECT_MODE.

If Python was built as a 64-bit executable then the AIX utilities that work with binary files (e.g., .o, and .a) may need the flag -X64. Rather than provide this flag with every command, the preferred way to provide this setting is to use the environment variable OBJECT_MODE. Depending on whether Python was build as a 32-bit or a 64-bit executable you may need to set or unset the environment variable OBJECT_MODE.

To determine the size the following command can be used:

$ python -c "import sys; print(sys.maxsize <= 2**32)"

When the answer is True (as above) Python was build as a 32-bit executable.

When working with a 32-bit Python executable proceed as follows:

./waf configure all

When working with a 64-bit Python executable proceed as follows:

export OBJECT_MODE=64
./waf configure all


The correct setting of OBJECT_MODE is also needed when you use PyInstaller to package your application.

To build the bootloader you will need a compiler compatible (identical) with the one used to build python.


Python compiled with a different version of gcc that you are using might not be compatible enough. GNU tools are not always binary compatible.

If you do not know which compiler that was, this command can help you determine if the compiler was gcc or an IBM compiler:

python -c "import sysconfig; print(sysconfig.get_config_var('CC'))"

If the compiler is gcc you may need additional RPMs installed to support the GNU run-time dependencies.

When the IBM compiler is used no additional prerequisites are expected. The recommended value for CC with the IBM compilers is :command:xlc_r.

Building for FreeBSD

A FreeBSD bootloader may be built with clang using the usual steps on a FreeBSD machine. Beware, however that any executable compiled natively on FreeBSD will only run on equal or newer versions of FreeBSD. In order to support older versions of FreeBSD, you must compile the oldest OS version you wish to support.

Alternatively, the FreeBSD bootloaders may be cross compiled from Linux using Docker and a FreeBSD cross compiler image. This image is kept in sync with the oldest non end of life FreeBSD release so that anything compiled on it will work on all active FreeBSD versions.

In a random directory:

  • Start the docker daemon (usually with systemctl start docker - possibly requiring sudo if you haven’t setup rootless docker).

  • Download the latest cross compiler .tar.xz image from here.

  • Import the image: docker image load -i freebsd-cross-build.tar.xz. The cross compiler image is now saved under the name freebsd-cross-build. You may discard the .tar.xz file if you wish.

Then from the root of this repository:

  • Run:

    docker run -v $(pwd):/io -it freebsd-cross-build bash -c "cd /io/bootloader; ./waf all"

Vagrantfile Virtual Machines

PyInstaller maintains a set of virtual machine description for testing and (cross-) building. For managing these boxes, we use vagrant.

All guests 3 will automatically build the bootloader when running vagrant up GUEST or vagrant provision GUEST. They will build both 32- and 64-bit bootloaders.


Except of guest osxcross, which will build the OS X SDK and cctools as described in section Cross-Building for macOS.

When building the bootloaders, the guests are sharing the PyInstaller distribution folder and will put the built executables onto the build-host (into ../PyInstaller/bootloader/).

Most boxes requires two Vagrant plugins to be installed:

vagrant plugin install vagrant-reload vagrant-scp

Example usage:

vagrant up linux64      # will also build the bootloader
vagrant halt linux64    # or `destroy`

# verify the bootloader has been rebuild
git status ../PyInstaller/bootloader/

You can pass some parameters for configuring the Vagrantfile by setting environment variables, like this:

GUI=1 TARGET=OSX vagrant up linux64

or like this:

vagrant provision linux64

We currently provide this guests:


GNU/Linux (some recent version) used to build the GNU/Linux bootloaders.

  • If TARGET=OSX is set, cross-builds the bootloaders for macOS (see Cross-Building for macOS).

  • If TARGET=WINDOWS is set, cross-builds the bootloaders for Windows using mingw. Please have in mind that this imposes the restrictions mentioned above.

  • Otherwise (which is the default) bootloaders for GNU/Linux are build.


Windows 10, used for building the Windows bootloaders using Visual C++.

  • If MINGW=1 is set, the bootloaders will be build using MinGW. Please be aware of the restrictions mentioned above.


The Windows box uses password authentication, so in some cases you need to enter the password (which is Passw0rd!).


GNU/Linux guest used to build the OS X SDK and cctools as described in section Cross-Building for macOS.