docs/chromeos_build_instructions.md

# Chrome OS Build Instructions (Chromium OS on Linux)

Chromium on Chromium OS is built from a mix of code sourced from Chromium
on Linux and Chromium on Windows. Much of the user interface code is
shared with Chromium on Windows.

If you make changes to Chromium on Windows, they may affect Chromium
on Chromium OS. Fortunately to test the effects of your changes you
don't need to build all of Chromium OS, you can just build Chromium for
Chromium OS directly on Linux.

First, follow the [normal Linux build
instructions](https://chromium.googlesource.com/chromium/src/+/master/docs/linux_build_instructions.md)
as usual to get a Chromium checkout.

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

If you plan to test the Chromium build on your dev machine and not a
Chromium OS device, run the following in your chromium checkout:

    $ gn gen out/Default --args='target_os="chromeos"'
    $ ninja -C out/Default -j32

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)
or DebugCros or whatever you like.

NOTE: If using goma increase -j32 (which controls parallelization) to something
higher, 500 or 1000. Consider adding `-l20` which prevents ninja from starting
jobs if the load average is too high - this prevents system hangs when using
-j1000 when goma is down.

See [GN Build Configuration](https://www.chromium.org/developers/gn-build-configuration)
for more information about configuring your build.

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

    is_component_build = true
    use_goma = true
    is_debug = false  # Release build, significantly faster
    dcheck_always_on = true  # Enable DCHECK (with is_debug = false)

    # Set the following true to create a Chrome (instead of Chromium) build.
    is_official_build = false
    is_chrome_branded = false

## 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=osmesa`, but it's ultra slow, and you'll have to build osmesa
    yourself.

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

To specify a logged in user:

*   For first run, add the following options to the command line:
    `--user-data-dir=/tmp/chrome --login-manager`
*   Go through the out-of-the-box UX and sign in as
    **username@gmail.com**.
*   For subsequent runs, add the following to the command line:
    `--user-data-dir=/tmp/chrome --login-user=username@gmail.com`
*   To run in guest mode instantly, you can run add the arguments:
    `--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.

## Compile Chromium for a Chromium OS device using the Chromium OS SDK

See [Building Chromium for a Chromium OS device](https://www.chromium.org/chromium-os/how-tos-and-troubleshooting/building-chromium-browser)
for information about building and testing chromium for Chromium OS.