Checking out and building on Fuchsia

Note that the Fuchsia port is in the early stages, and things are likely to frequently be broken. Try #cr-fuchsia on Freenode or Slack if something seems awry.

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 supported on a best-effort basis.

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.

$ fetch --nohooks chromium

Expect the command to take 30 minutes on even a fast connection, and many hours on slower ones.

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']

You will then need to run:

$ gclient runhooks

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/master). 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.


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!

(Recommended)(Linux-only) Enable KVM acceleration

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:
$ sudo apt-get install qemu-system-common
  1. Add users to the “kvm” group, and have them login again, to pick-up the new group.

Running test suites

Building test suites generate a launcher script to run them on an emulator or a physical device. These scripts are generated at out/fuchsia/bin. For instance,to run the base_unittests target, launch:

$ out/fuchsia/bin/run_base_unittests

Common gtest arguments such as --gtest_filter=... are supported by the run script. The launcher script also symbolizes backtraces.

The test suite, by default, will run on QEMU. AEMU can be used for running tests that interact with Fuchsia's window manager, Scenic. To change the device that Fuchsia will run on, use --device={aemu|qemu|device}.

To run a test suite on an unprovisioned device in a zedboot state, simply add -d to the test runner script arguments. Subsequent runs of the test runner script will be able to pick up the same device.

To run a test suite on a device that is already provisioned, add the following arguments to the test runner script:

  • -d to run the test suite on a device.
  • --fuchsia-out-dir=[/path/to/fuchsia/out/directory] or --ssh-config=[/path/to/ssh_config] to specify the SSH configuration used for connecting to the target device.
  • (Optional) --host=[IP] to specify the test device IP. Typically, this is the value obtained from the command fx netaddr --fuchsia.
  • (Optional) --port=[port] to specify the SSH port, if different from 22.

Troubleshooting a test

To troubleshoot a specific test, consider a combination of the following arguments to the test runner script:

  • --gtest_filter="[TestSuite.TestName]" to only run a specific test, or a comma-separated list to run a set of tests. Wildcards can also be used to run a set of tests or an entire test suite, e.g. --gtest_filter="[TestSuite.*]".
  • --test-launcher-jobs=1 to only have one batch of tests running at a time. This bypasses the test launcher buffering of test log output, making it possible to access the log output from successful test runs.
  • --single-process-tests to run all the tests in the same process. Unlike the above option, this will run the tests directly in the test launcher process, making it easier to attach a debugger.
  • system-log-file=[/path/to/syslog] to specify the file to write system logs to. Or system-log-file=- to write the system logs to stdout. By default, Chromium logs are written to the system log on Fuchsia. This argument is known to cause IOError python exceptions with a QEMU target.
  • --gtest_repeat=[number] --gtest_break_on_failure to run a test or test suite a certain number of times until it fails. This is useful to investigate flaky tests.