ACRN Documentation Generation

These instructions will walk you through generating the Project ACRN’s documentation and publishing it to You can also use these instructions to generate the ACRN documentation on your local system.

Documentation Overview

Project ACRN content is written using the reStructuredText markup language (.rst file extension) with Sphinx extensions, and processed using Sphinx to create a formatted stand-alone website. Developers can view this content either in its raw form as .rst markup files, or you can generate the HTML content and view it with a web browser directly on your workstation.

You can read details about reStructuredText, and Sphinx from their respective websites.

The project’s documentation contains the following items:

  • ReStructuredText source files used to generate documentation found at the website. All of the reStructuredText sources are found in the acrn-hypervisor/doc folder, or pulled in from sibling folders (such as misc/) by the build scripts.

  • Doxygen-generated material used to create all API-specific documents found at The documentation build process uses doxygen to scan source files in the hypervisor and device-model folders, and from sources in the acrn-kernel repo (as explained later).


The reStructuredText files are processed by the Sphinx documentation system and use the breathe extension for including the doxygen-generated API material.

Set Up the Documentation Working Folders

You’ll need git installed to get the working folders set up:

  • For an Ubuntu development system use:

    sudo apt install git

We use the source header files to generate API documentation and we use for publishing the generated documentation. Here’s the recommended folder setup for documentation contributions and generation:

The parent projectacrn folder is there because, if you have repo publishing rights, we’ll also be creating a publishing area later in these steps. For API documentation generation, we’ll also need the acrn-kernel repo contents in a sibling folder to the acrn-hypervisor repo contents.

It’s best if the acrn-hypervisor folder is an ssh clone of your personal fork of the upstream project repos (though https clones work too and won’t require you to register your public SSH key with GitHub):

  1. Use your browser to visit and do a fork of the acrn-hypervisor repo to your personal GitHub account.)

  2. At a command prompt, create the working folder and clone the acrn-hypervisor repository to your local computer (and if you have publishing rights, the repo). If you don’t have publishing rights you’ll still be able to generate the documentation files locally, but not publish them:

    cd ~
    mkdir projectacrn && cd projectacrn
    git clone<github-username>/projectacrn/acrn-hypervisor.git
  3. For the cloned local repos, tell git about the upstream repo:

    cd acrn-hypervisor
    git remote add upstream

    After that, you’ll have origin pointing to your cloned personal repo and upstream pointing to the project repo.

  4. For API documentation generation we’ll also need the acrn-kernel repo available locally into the acrn-hypervisor folder:

    cd ..
    git clone


    We assume for documentation generation that origin is pointed to the upstream acrn-kernel repo. If you’re a developer and have the acrn-kernel repo already set up as a sibling folder to the acrn-hypervisor, you can skip this clone step.

  5. If you haven’t done so already, be sure to configure git with your name and email address for the signed-off-by line in your commit messages:

    git config --global "David Developer"
    git config --global ""

Install the Documentation Tools

Our documentation processing has been tested to run with Python 3.6.3 and these other tools:

  • breathe version: 4.23.0

  • sphinx version: 3.2.1

  • docutils version: 0.16

  • sphinx-rtd-theme version: 0.5.0

  • sphinx-tabs version: 1.3.0

  • doxygen version: 1.8.13

Depending on your Linux version, install the needed tools. You may get a different (newer) version of doxygen noted above that may also work.

For Ubuntu use:

sudo apt install doxygen python3-pip \
  python3-wheel make graphviz xsltproc

Then use pip3 to install the remaining Python-based tools:

cd ~/projectacrn/acrn-hypervisor/doc
pip3 install --user -r scripts/requirements.txt

Use this command to add $HOME/.local/bin to the front of your PATH so the system will find expected versions of these Python utilities such as sphinx-build and breathe:

printf "\nexport PATH=\$HOME/.local/bin:\$PATH" >> ~/.bashrc


You will need to open a new terminal for this change to take effect. Adding this to your ~/.bashrc file ensures it is set by default.

And with that you’re ready to generate the documentation.


We’ve provided a script you can run to show what versions of the documentation building tools are installed and compare with the tool versions shown above.:


Extra Tools for Generating PDF

While the primary output for ACRN documentation is for an HTML website, you can also generate a PDF version of the documentation. A few extra tools are needed only if you want to create PDF output. For Ubuntu users add these additional packages:

sudo apt install texlive-latex-recommended texlive-fonts-recommended \
  texlive-latex-extra latexmk texlive-xetex xindy

Documentation Presentation Theme

Sphinx supports easy customization of the generated HTML documentation appearance through the use of themes. Replace the theme files and do another make html and the output layout and style is changed. The sphinx build system creates document cache information that attempts to expedite documentation rebuilds, but occasionally can cause an unexpected error or warning to be generated. Doing a make clean to create a clean generation environment and a make html again generally fixes these issues.

The read-the-docs theme is installed as part of the requirements.txt list above. Tweaks to the standard read-the-docs appearance are added by using CSS and JavaScript customization found in doc/static, and theme template overrides found in doc/_templates.

Run the Documentation Processors

The acrn-hypervisor/doc directory has all the .rst source files, extra tools, and Makefile for generating a local copy of the ACRN technical documentation. (Some additional .rst files and other material is extracted or generated from the /misc folder as part of the Makefile.) For generating all the API documentation, there is a dependency on having the acrn-kernel repo’s contents available too (as described previously). You’ll get a sphinx warning if that repo is not set up as described, but you can ignore that warning if you’re not planning to publish or show the API documentation.

cd ~/projectacrn/acrn-hypervisor/doc
make html

Depending on your development system, it will take less than two minutes to collect and generate the HTML content. When done, you can view the HTML output with your browser started at ~/projectacrn/acrn-hypervisor/doc/_build/html/index.html. You can also cd to the _build/html folder and run a local web server with the command:

cd _build/html
python3 -m http.server

and use your web browser to open the URL: http://localhost:8000.

Generate PDF Output

After the HTML content is generated, it leaves artifacts behind that you can use to generate PDF output using the Sphinx latex builder. This builder initially creates LaTeX output in the _build/latex folder and then uses the latexmk tool to create the final acrn.pdf file in the same folder. This process automatically makes a few passes over the content to create the index and resolve intra-document hyperlinks, and produces plenty of progress messages along the way. The Sphinx-generated output for tables and code blocks also yields many “underfill” and “overfill” messages from the latex builder that can’t be easily suppressed or fixed. Because of that, we recommend running this PDF generation with the -silent options, like this (after you’ve run make html:

make latexpdf LATEXMKOPTS="-silent"

For convenience, we’ve also created a make target called pdf that will first generate the HTML content and then make the PDF file in one step:

make pdf

This make target runs quietly, and then verifies that no unexpected message from the build process are produced (using the message filtering process explained below. Either way, when the build completes, the generated PDF file is in _build/latex/acrn.pdf.

Publish Content

If you have merge rights to the projectacrn repo called, you can update the public project documentation found at

You’ll need to do a one-time clone of the upstream repo (we publish directly to the upstream repo rather than to a personal forked copy):

cd ~/projectacrn
git clone

Then, after you’ve verified the generated HTML from make html looks good, you can push directly to the publishing site with:

make publish

This uses git commands to synchronize the new content with what’s already published and will delete files in the publishing repo’s latest folder that are no longer needed. New or changed files from the newly-generated HTML content are added to the GitHub pages publishing repo. The public site at will be updated by the GitHub pages system, typically within a few minutes.

Document Versioning

The site has a document version selector at the top of the left nav panel. The contents of this version selector are defined in the sphinx configuration file, specifically:

html_context = {
   'current_version': current_version,
   'docs_title': docs_title,
   'is_release': is_release,
   'versions': ( ("latest", "/latest/"),
                 ("2.3", "/2.3/"),
                 ("2.2", "/2.2/"),
                 ("2.1", "/2.1/"),
                 ("2.0", "/2.0/"),
                 ("1.6.1", "/1.6.1/"),
                 ("1.6", "/1.6/"),
                 ("1.5", "/1.5/"),
                 ("1.4", "/1.4/"),
                 ("1.0", "/1.0/"),   # keep 1.0

As new versions of ACRN documentation are added, update this versions selection list to include the version number and publishing folder. Note that there’s no direct selection to go to a newer version from an older one, without going to latest first.

By default, documentation build and publishing both assume we’re generating documentation for the main branch and publishing to the /latest/ area on When we’re generating the documentation for a tagged version (e.g., 2.3), check out that version of the repo, and add some extra flags to the make commands:

cd ~/projectacrn/acrn-hypervisor/doc
git checkout v2.3
make clean
make DOC_TAG=release RELEASE=2.3 html
make DOC_TAG=release RELEASE=2.3 publish

Filter Expected Warnings

Alas, there are some known issues with the doxygen/Sphinx/Breathe processing that generates warnings for some constructs, in particular around unnamed structures in nested unions or structs. While these issues are being considered for fixing in Sphinx/Breathe, we’ve added a post-processing filter on the output of the documentation build process to check for “expected” messages from the generation process output.

The output from the Sphinx build is processed by the Python script scripts/ together with a set of filter configuration files in the .known-issues/doc folder. (This filtering is done as part of the Makefile.)

If you’re contributing components included in the ACRN API documentation and run across these warnings, you can include filtering them out as “expected” warnings by adding or editing a conf file in the .known-issues/doc folder, following the example of other conf files found there.