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Chrome OS Build Instructions

Chrome for Chromium OS can be built in a couple different ways. After following the initial setup, you'll need to choose one of the following build configurations:

  • If you're interested in testing Chrome OS code in Chrome, but not interactions with Chrome OS services, you can build for linux-chromeos using just a Linux workstation.
  • Otherwise, Chrome's full integration can be covered by building for a real Chrome OS device or VM using Simple Chrome.
  • Use is_chromeos_device in GN and BUILDFLAG(IS_CHROMEOS_DEVICE) in C++ code to differentiate between these two modes.

[TOC]

Common setup

First, follow the normal Linux build instructions as usual to get a Chromium checkout.

You'll also need to add 'chromeos' to the target_os list in your .gclient configuration, which will fetch the additional build dependencies required for CrOS. This file is located one level up from your Chromium checkout's src.

If you don't already have a target_os line present, simply add this to the end of the .gclient file:

target_os = ['chromeos']

If you already have a target_os line present in your .gclient file, you can simply append 'chromeos' to the existing list there. For example:

target_os = ['android', 'chromeos']

Once your .gclient file is updated, you will need to run gclient sync once before proceeding with the rest of these instructions.

Chromium OS on Linux (linux-chromeos)

Chromium on Chromium OS uses Linux Chromium as a base, but adds a large number of Chrome OS-specific features to the code. For example, the login UI, window manager and system UI are part of the Chromium code base and built into the chrome binary.

Fortunately, most Chromium changes that affect Chromium OS can be built and tested on a Linux workstation. This build is called "linux-chromeos". In this configuration most system services (like the power manager, bluetooth daemon, etc.) are stubbed out. The entire system UI runs in a single X11 window on your desktop.

You can test sign-in/sync in this mode by adding the --login-manager flag, see the Login notes section.

Building and running Chromium with Chromium OS UI on your local machine

Run the following in your chromium checkout:

$ gn gen out/Default --args='target_os="chromeos"'
$ autoninja -C out/Default chrome
$ out/Default/chrome --use-system-clipboard

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

Some additional options you may wish to set by passing in --args to gn gen or running gn args out/Default:

use_goma = true            # Googlers: Use build farm, compiles faster.
is_component_build = true  # Links faster.
is_debug = false           # Release build, runs faster.
dcheck_always_on = true    # Enables DCHECK despite release build.
enable_nacl = false        # Skips native client build, compiles faster.

# Set the following true to create a Chrome (instead of Chromium) build.
# This requires a src-internal checkout.
is_chrome_branded = false  # Adds internal features and branded art assets.
is_official_build = false  # Turns on many optimizations, slower build.

NOTE: You may wish to replace 'Default' with something like 'Cros' if you switch back and forth between Linux and Chromium OS builds, or 'Debug' if you want to differentiate between Debug and Release builds (see below).

See GN Build Configuration for more information about configuring your build.

You can also build and run test targets like unit_tests, browser_tests, etc.

Flags

Some useful flags:

  • --ash-debug-shortcuts: Enable shortcuts such as Ctl+Alt+Shift+T to toggle tablet mode.
  • --ash-host-window-bounds="0+0-800x600,800+0-800x600": Specify one or more virtual screens, by display position and size.
  • --enable-features=Feature1,OtherFeature2: Enable specified features. Features are often listed in chrome://flags, or in source files such as chrome_features.cc or ash_features.cc. Note that changing values in chrome://flags does not work for linux-chromeos, and this flag must be used.
  • --enable-ui-devtools[=9223]: Allow debugging of the system UI through devtools either within linux-chromeos at chrome://inspect, or from a remote browser at devtools://devtools/bundled/devtools_app.html?uiDevTools=true&ws=127.0.0.1:9223/0
  • --remote-debugging-port=9222: Allow debugging through devtools at http://localhost:9222
  • --use-system-clipboard: Integrate clipboard with the host X11 system.

Login notes

By default this build signs in with a stub user. To specify a real user:

  • For first run, add the following options to chrome's command line: --user-data-dir=/tmp/chrome --login-manager
  • Go through the out-of-the-box UX and sign in with a real Gmail account.
  • For subsequent runs, if you want to skip the login manager page, add: --user-data-dir=/tmp/chrome --login-user=username@gmail.com --login-profile=username@gmail.com-hash. It's also fine to just keep --login-manager instead.
  • To run in guest mode instantly, add: --user-data-dir=/tmp/chrome --bwsi --incognito --login-user='$guest' --login-profile=user

Signing in as a specific user is useful for debugging features like sync that require a logged in user.

Graphics notes

The Chromium OS build requires a functioning GL so if you plan on testing it through Chromium Remote Desktop you might face drawing problems (e.g. Aura window not painting anything). Possible remedies:

  • --ui-enable-software-compositing --ui-disable-threaded-compositing
  • --use-gl=swiftshader, but it's slow.

To more closely match the UI used on devices, you can install fonts used by Chrome OS, such as Roboto, on your Linux distro.

Chromium OS Device (Simple Chrome)

This configuration allows you to build a fully functional Chrome for a real Chrome OS device or VM. Since Chrome OS uses a different toolchain for each device model, you'll first need to know the name of the model (or "board") you want to build for. For most boards, amd64-generic and arm-generic will produce a functional binary, though it won't be optimized and may be missing functionality.

Additional gclient setup

Each board has its own toolchain and misc. build dependencies. To fetch these, list the board under the "cros_boards" gclient custom var. If you were using the amd64-generic board, your .gclient file would look like:

solutions = [
  {
    "url": "https://chromium.googlesource.com/chromium/src.git",
    "name": "src",
    "custom_deps": {},
    "custom_vars" : {
        "cros_boards": "amd64-generic",
    },
  },
]
target_os = ["chromeos"]

Once your .gclient file is updated, you will need to run gclient sync again to fetch the toolchain.

NOTE:

  • If you'd like a VM image additionally downloaded for the board, add it to the "cros_boards_with_qemu_images" gclient custom var. That var downloads the SDK along with a VM image. cros_boards downloads only the SDK.
  • If you'd like to fetch multiple boards, add a : between each board in the gclient var. For example: "cros_boards": "amd64-generic:arm-generic".

Building for the board

After the needed toolchain has been downloaded for your ${BOARD}, a build dir will have been conveniently created for you at out_$BOARD/Release, which can then be used to build Chrome. For the amd64-generic board, this would look like:

$ gn gen out_amd64-generic/Release
$ autoninja -C out_$BOARD/Release chrome

Or if you prefer to use your own build dir, simply add the following line to the top of your GN args: import("//build/args/chromeos/amd64-generic.gni"). eg:

$ gn gen out/Default --args='import("//build/args/chromeos/amd64-generic.gni")'
$ autoninja -C out/Default chrome

That will produce a Chrome OS build of Chrome very similar to what is shipped for that device. You can also supply additional args or even overwrite ones supplied in the imported .gni file after the import() line.

Additional notes

For more information (like copying the locally-built Chrome to a device, or running Tast tests), consult Simple Chrome's full documentation.