Checking out and building on Fuchsia

If you have followed the instructions below and are still having trouble, see Contact information.

There are instructions for other platforms linked from the get the code page.

System requirements

  • A 64-bit Intel machine with at least 8GB of RAM. More than 16GB is highly recommended.
  • At least 100GB of free disk space.
  • You must have Git and Python installed already.

Most development is done on Ubuntu. Mac build is not supported. If you already have a Chromium checkout, continue to the next section. Otherwise, skip to the following section. If you are a Fuchsia developer, see also Working with the Fuchsia tree.

Instructions for current Chromium developers

This section applies to you if you already have a Chromium checkout. You will need to update it to install Fuchsia-specific dependencies.

  1. Edit your .gclient to add fuchsia to the target_os list. The file should look similar to this:

    solutions = [
        "url": "",
        "managed": False,
        "name": "src",
        "custom_deps": {},
        "custom_vars": {}
    target_os = ['fuchsia']
  2. Run gclient sync

  3. Create a build directory:

    $ gn gen out/fuchsia --args="is_debug=false dcheck_always_on=true is_component_build=false target_os=\"fuchsia\""

    You can add many of the usual GN arguments like use_goma = true. In particular, when working with devices, consider using is_debug = false and is_component_build = false since debug and component builds can drastically increase run time and used space.

Build the target as you would for any other platform:

$ autoninja out/fuchsia <target_name>

To run the tests in an emulator, see the Run section.

Instructions for new Chromium developers

Install depot_tools

Clone the depot_tools repository:

$ git clone

Add depot_tools to the end of your PATH (you will probably want to put this in your ~/.bashrc or ~/.zshrc). Assuming you cloned depot_tools to /path/to/depot_tools:

$ export PATH="$PATH:/path/to/depot_tools"

Get the code

Create a chromium directory for the checkout and change to it (you can call this whatever you like and put it wherever you like, as long as the full path has no spaces):

$ mkdir ~/chromium && cd ~/chromium

Run the fetch tool from depot_tools to check out the code and its dependencies. Depending on your needs, you can check out Chromium along with all of its previous revisions, or you can just check out the latest trunk. Omitting the history is much faster to download and requires much less disk space. If you are checking out on a slow or metered Internet connection, you should consider omitting history.

  • No Git version history - faster
  $ fetch --nohooks --no-history chromium
  • With Git version history - slower (up to 30m on fast connection)
$ fetch --nohooks chromium

If you've already installed the build dependencies on the machine (from another checkout, for example), you can omit the --nohooks flag and fetch will automatically execute gclient runhooks at the end.

When fetch completes, it will have created a hidden .gclient file and a directory called src in the working directory.

Configure for building on Fuchsia

Edit .gclient to include (this is a list, so it could also include android, etc. if necessary.)

target_os = ['fuchsia']

Note that this should be added as a top-level statement in the .gclient file, not an entry inside the solutions dict. An example .gclient file would look as follows:

solutions = [
    "url": "",
    "managed": False,
    "name": "src",
    "custom_deps": {},
    "custom_vars": {}
target_os = ['fuchsia']

The Fuchsia boot images (also called “SDK companion images”) to check out are specified by the checkout_fuchsia_boot_images variable. For instance, adding "checkout_fuchsia_boot_images": "qemu.x64,workstation.qemu-x64-release", to the custom_vars section of your .gclient file would allow you to check out both images. The set of available images is listed in the DEPS file.

Note: tracks migration away from the legacy image names, like qemu.x64, which is mapped to terminal.x64-release by the helper script.

You will then need to run:

$ gclient sync

This makes sure the Fuchsia SDK is available in third_party and keeps it up to date.

The remaining instructions assume you have switched to the src directory:

$ cd src

(Linux-only) Install any required host packages

Chromium relies on some platform packages to be present in order to build. You can install the current set of required packages with:

$ build/

Note that you need to do this only once, and thereafter only if new dependencies are added - these will be announced to the chromium-dev@ group.

Update your checkout

To update an existing checkout, you can run

$ git rebase-update
$ gclient sync

The first command updates the primary Chromium source repository and rebases any of your local branches on top of tip-of-tree (aka the Git branch origin/main). If you don't want to use this script, you can also just use git pull or other common Git commands to update the repo.

The second command syncs dependencies to the appropriate versions and re-runs hooks as needed. gclient sync updates dependencies to the versions specified in DEPS, so any time that file is modified (pulling, changing branches, etc.) gclient sync should be run.

(Mac-only) Download additional required Clang binaries

Go to this page and download the most recent build. Extract bin/llvm-ar to the clang folder in Chromium:

$ unzip /path/to/ bin/llvm-ar -d ${CHROMIUM_SRC}/third_party/llvm-build/Release+Asserts

Setting up the build

Chromium uses Ninja as its main build tool along with a tool called GN to generate .ninja files. You can create any number of build directories with different configurations. To create a build directory, run:

$ gn gen out/fuchsia --args="is_debug=false dcheck_always_on=true is_component_build=false target_os=\"fuchsia\""

You can also build for Debug, with is_debug=true, but since we don't currently have any Debug build-bots, it may be more broken than Release.

use_goma=true is fine to use also if you're a Googler.

Architecture options are x64 (default) and arm64. This can be set with target_cpu=\"arm64\".


All targets included in the GN build should build successfully. You can also build a specific binary, for example, base_unittests:

$ autoninja -C out/fuchsia base_unittests

(autoninja is a wrapper that automatically provides optimal values for the arguments passed to ninja.)


Once you‘ve built a package, you’ll want to run it!

(Linux-only) Enable KVM acceleration (strongly recommended)

Under Linux, if your host and target CPU architectures are the same (e.g. you‘re building for Fuchsia/x64 on a Linux/x64 host) then you can benefit from QEMU’s support for the KVM hypervisor:

  1. Install the KVM module for your kernel, to get a /dev/kvm device.
  2. Ensure that your system has a “kvm” group, and it owns /dev/kvm. You can do that by installing the QEMU system common package: shell $ sudo apt-get install qemu-system-common
  3. Add users to the “kvm” group, and have them login again, to pick-up the new group. shell $ sudo adduser <user> kvm $ exit [log in again]

Running test suites

There are four types of tests available to run on Fuchsia:

  1. Gtests
  2. GPU integration tests
  3. Blink tests
  4. Webpage tests

Check the documentations to learn more about how to run these tests.

Documentation for the underlying testing scripts work can be found here.

Working with the Fuchsia tree

If you have a Fuchsia checkout and build, there are GN arguments in Chromium that make working with both Fuchsia and Chromium checkouts easier.

  • default_fuchsia_out_dir. Point this to an output directory in Fuchsia. For instance. /path/to/src/fuchsia/out/qemu-x64. This will automatically add the --fuchsia-out-dir flag to wrapper scripts.
  • default_fuchsia_device_node_name. Set this to a Fuchsia device node name. This will automatically add the --target-id flag to most wrapper scripts.
  • Finally, use the -d flag when running the <test_target_name> wrappers to execute them on an already running device or emulator, rather than starting an ephemeral emulator instance. This speeds up subsequent runs since the runner script does not need to wait for the emulator instance to boot and only differential changes are pushed to the device.