- Build targets
- Build dependencies
- Downloading source code
- Development branch
- Stable release
- Updating and switching branches or tags
- Setting up the OS build environment
- Reproducible builds
- Extracting vendor files for Pixel devices
- Faster builds for development use only
- Generating release signing keys
- Generating signed factory images and full update packages
- Prebuilt code
- Standalone SDK
- Development guidelines
- aosp_taimen (Pixel 2 XL)
- aosp_walleye (Pixel 2)
- aosp_crosshatch (Pixel 3 XL)
- aosp_blueline (Pixel 3)
- aosp_bonito (Pixel 3a XL)
- aosp_sargo (Pixel 3a)
These are all fully supported production-ready targets supporting all the baseline security features and receiving full monthly security updates covering all firmware, kernel drivers, driver libraries / services and other device-specific code. A fully signed user build for these devices is a proper GrapheneOS release. Newer generation devices have stronger hardware / firmware security and hardware-based OS security features and are better development devices for that reason. It's not possible to work on everything via past generation devices. The best development devices are the Pixel 3, Pixel 3 XL, Pixel 3a and Pixel 3a XL.
These generic targets can be used with the emulator along with many smartphones, tablets and other devices. These targets don't receive full monthly security updates, don't offer all of the baseline security features and are intended for development usage.
Providing proper support for a device or generic device family requires providing an up-to-date kernel and device support code including driver libraries, firmware and device SELinux policy extensions. Other than some special cases like the emulator, the generic targets rely on the device support code present on the device. Shipping all of this is necessary for full security updates and is tied to enabling verified boot / attestation. Pixel targets have a lot of device-specific hardening in the AOSP base along with some in GrapheneOS which needs to be ported over too. For example, various security features in the kernel including type-based Control Flow Integrity (CFI) and the shadow call stack are currently specific to the kernels for these devices.
SDK emulator targets:
These are extended versions of the generic targets with extra components for the SDK. These targets don't receive full monthly security updates, don't provide all of the baseline security features and are intended for development usage.
The hikey and hikey960 targets are not actively tested and have unresolved upstream memory corruption bugs uncovered by GrapheneOS security features. It boots, but there are major issues with the graphics drivers among other problems. The intention is to support them, but the necessary time has not yet been dedicated to it. These targets don't receive full monthly security updates, don't provide all of the baseline security features and are intended for development usage.
- x86_64 Linux build environment (macOS is not supported, unlike AOSP which partially supports it)
- Android Open Source Project build dependencies
- Linux kernel build dependencies
- 16GiB of memory or more
- 300GiB of free storage space
Since this is syncing the sources for the entire operating system and application layer, it will use a lot of bandwidth and storage space.
You likely want to use the most recent stable tag, not the development branch, even for developing a feature. It's easier to port between stable tags that are known to work properly than dealing with a moving target.
10 branch is the only active development branch for GrapheneOS
development. Older branches are no longer maintained. It is currently used for all
officially supported devices and should be used for the basis of ports to other
devices. Occasionally, some devices may be supported through device support branches
to avoid impacting other devices with changes needed to support them.
mkdir grapheneos-10 cd grapheneos-10 repo init -u https://github.com/GrapheneOS/platform_manifest.git -b 10 repo sync -j32
If your network is unreliable and
repo sync fails, you can run the
repo sync command again as many times as needed for it to fully
Pick a specific build for a device from the releases page and download the source tree. Note that some devices use different Android Open Source Project branches so they can end up with different tags. Make sure to use the correct tag for a device. For devices without official support, use the latest tag for the Pixel 3.
mkdir grapheneos-TAG_NAME cd grapheneos-TAG_NAME repo init -u https://github.com/GrapheneOS/platform_manifest.git -b refs/tags/TAG_NAME
Verify the manifest:
gpg --recv-keys 65EEFE022108E2B708CBFCF7F9E712E59AF5F22A gpg --recv-keys 4340D13570EF945E83810964E8AD3F819AB10E78 cd .repo/manifests git verify-tag --raw $(git describe) cd ../..
Complete the source tree download:
repo sync -j32
Verify the source tree:
repo forall -c 'git verify-tag --raw $(git describe)' || echo Verification failed!
These instructions will be extended in the future to check the verify-tag output.
Note that the repo command itself takes care of updating itself and uses gpg to verify by default.
To update the source tree, run the
repo init command again to select
the branch or tag and then run
repo sync -j32 again. You may need to add
--force-sync if a repository switched from one source to another,
such as when GrapheneOS forks an additional Android Open Source Project repository.
You don't need to start over to switch between different branches or tags. You may
need to run
repo init again to continue down the same branch since
GrapheneOS only provides a stable history via tags.
The kernel needs to be built in advance, since it uses a separate build system.
List of kernels corresponding to officially supported devices:
- Pixel 2, Pixel 2 XL: wahoo - separate taimen and walleye builds due to hardening
- Pixel 3, Pixel 3 XL, Pixel 3a, Pixel 3a XL: crosshatch - separate crosshatch, blueline and bonito builds due to hardening
As part of the hardening in GrapheneOS, it uses fully monolithic kernel builds with dynamic kernel modules disabled. This improves the effectiveness of mitigations like Control Flow Integrity benefiting from whole program analysis. It also reduces attack surface and complexity including making the build system simpler. The kernel trees marked as using a separate build above need to have the device variant passed to the GrapheneOS kernel build script to select the device.
For the Pixel 3, Pixel 3 XL, Pixel 3a and Pixel 3a XL, the kernel repository uses
submodules for building in out-of-tree modules. You need to make sure the submodule
sources are updated before building. In the future, this should end up being handled
repo. There's no harm in running the submodule commands
for other devices as they will simply not do anything.
For example, to build the kernel for blueline:
cd kernel/google/crosshatch git submodule sync git submodule update --init ./build.sh blueline
kernel/google/wahoo repository is for the Pixel 2 and Pixel 2 XL
kernel/google/crosshatch repository is for the Pixel 3, Pixel 3
XL, Pixel 3a and Pixel 3a XL.
The build has to be done from bash as envsetup.sh is not compatible with other shells like zsh.
Set up the build environment:
Select the desired build target (
aosp_crosshatch is the Pixel 3 XL):
choosecombo release aosp_crosshatch user
For a development build, you may want to replace
userdebug in order to have better debugging support. Production builds
user builds as they are significantly more secure and don't
make additional performance sacrifices to improve debugging.
To reproduce a past build, you need to export
BUILD_NUMBER to the values set for the past build. These can be obtained
out/build_number.txt in a build
output directory and the
ro.build.version.incremental properties which are also included in the
over-the-air zip metadata rather than just the OS itself.
The signing process for release builds is done after completing builds and replaces the dm-verity trees, apk signatures, etc. and can only be reproduced with access to the same private keys. If you want to compare to production builds signed with different keys you need to stick to comparing everything other than the signatures.
This section does not apply to devices where no extra vendor files are required (HiKey, HiKey 960, emulator, generic targets).
Many of these components are already open source, but not everything is set up to be built by the Android Open Source Project build system. Switching to building these components from source will be an incremental effort. In many cases, the vendor files simply need to be ignored and AOSP will already provide them instead. Firmware cannot generally be built from source even when sources are available, other than to verify that the official builds match the sources, since it has signature verification (which is an important part of the verified boot and attestation security model).
Extract the vendor files corresponding to the matching release:
vendor/android-prepare-vendor/execute-all.sh -d DEVICE -b BUILD_ID -o vendor/android-prepare-vendor mkdir -p vendor/google_devices rm -rf vendor/google_devices/DEVICE mv vendor/android-prepare-vendor/DEVICE/BUILD_ID/vendor/google_devices/* vendor/google_devices/
Note that android-prepare-vendor is non-deterministic unless a timestamp parameter is
--timestamp (seconds since Epoch).
Incremental builds (i.e. starting from the old build) usually work for development and are the normal way to develop changes. However, there are cases where changes are not properly picked up by the build system. For production builds, you should remove the remnants of any past builds before starting, particularly if there were non-trivial changes:
rm -r out
Start the build process, with -j# used to set the number of parallel jobs to the number of CPU threads. You also need 2-4GiB of memory per job, so reduce it based on available memory if necessary:
make target-files-package -j20
For an emulator build, always use the development build approach below.
The normal production build process involves building a target files package to be resigned with secure release keys and then converted into factory images and/or an update zip via the sections below. If you have a dedicated development device with no security requirements, you can save time by using the default make target, leaving the bootloader unlocked and flashing the raw images that are signed with the default public test keys:
Technically, you could generate test key signed update packages. However, there's no point of sideloading update packages when the bootloader is unlocked and there's no value in a locked bootloader without signing the build using release keys, since verified boot will be meaningless and the keys used to verify sideloaded updates are also public. The only reason to use update packages or a locked bootloader without signing the build with release keys would be testing that functionality and it makes a lot more sense to test it with proper signing keys rather than the default public test keys.
Keys need to be generated for resigning completed builds from the publicly available test keys. The keys must then be reused for subsequent builds and cannot be changed without flashing the generated factory images again which will perform a factory reset. Note that the keys are used for a lot more than simply verifying updates and verified boot.
The keys should not be given passwords due to limitations in the upstream scripts. If you want to secure them at rest, you should take a different approach where they can still be available to the signing scripts as a directory of unencrypted keys. The sample certificate subject can be replaced with your own information or simply left as-is.
To generate keys for crosshatch (you should use unique keys per device variant):
mkdir -p keys/crosshatch cd keys/crosshatch ../../development/tools/make_key releasekey '/CN=GrapheneOS/' ../../development/tools/make_key platform '/CN=GrapheneOS/' ../../development/tools/make_key shared '/CN=GrapheneOS/' ../../development/tools/make_key media '/CN=GrapheneOS/' ../../development/tools/make_key networkstack '/CN=GrapheneOS/' openssl genrsa -out avb.pem 2048 ../../external/avb/avbtool extract_public_key --key avb.pem --output avb_pkmd.bin cd ../..
avb_pkmd.bin file isn't needed for generating a signed release but
rather to set the public key used by the device to enforce verified boot.
For Android 10, there's a new
networkstack key and you need to
generate one to avoid using the test key. For example, with crosshatch (needs to be
done for each set of device keys):
cd keys/crosshatch ../../development/tools/make_key networkstack '/CN=GrapheneOS/'
GrapheneOS disables updatable APEX components for the officially supported devices and targets inheriting from the mainline target, so APEX signing keys are not needed and this section can be ignored for unmodified builds.
GrapheneOS uses the
TARGET_FLATTEN_APEX := true format to include APEX
components as part of the base OS without supporting out-of-band updates.
If you don't disable updatable APEX packages, you need to generate an APK and AVB key for each APEX component and extend the GrapheneOS release.sh script to pass the appropriate parameters to replace the APK and AVB keys for each APEX component.
APEX components that are not flattened are a signed APK (used to verify updates) with an embedded filesystem image signed with an AVB key (for verified boot). Each APEX package must have a unique set of keys. GrapheneOS has no use for these out-of-band updates at this time and flattening APEX components avoids needing a bunch of extra keys and complexity.
For now, consult the upstream documentation on generating these keys. It will be covered here in the future.
Build the tool needed to generate A/B updates:
make -j20 brillo_update_payload
Generate a signed release build with the release.sh script:
The factory images and update package will be in
out/release-crosshatch-$BUILD_NUMBER. The update zip performs a full OS
installation so it can be used to update from any previous version. More efficient
incremental updates are used for official over-the-air GrapheneOS updates and can be
generated by keeping around past signed
target_files zips and generating
incremental updates from those to the most recent signed
Incremental updates shipping only the changes between two versions can be generated
as a much more efficient way of shipping updates than a full update package containing
the entire operating system. The GrapheneOS Updater app will automatically use a delta
update if one exists for going directly from the currently installed version to the
latest release. In order to generate a delta update, the original signed target files
package for both the source version and target version are needed. The
script/generate_delta.sh script provides a wrapper script for generating
delta updates by passing the device, source version build number and target version
build number. For example:
script/generate_delta.sh crosshatch 2019.09.25.00 2019.10.07.21
The script assumes that the releases are organized in the following directory structure:
releases ├── 2019.09.25.00 │ └── release-crosshatch-2019.09.25.00 │ ├── crosshatch-factory-2019.09.25.00.zip │ ├── crosshatch-factory-2019.09.25.00.zip.sig │ ├── crosshatch-img-2019.09.25.00.zip │ ├── crosshatch-ota_update-2019.09.25.00.zip │ ├── crosshatch-target_files-2019.09.25.00.zip │ └── crosshatch-testing └── 2019.10.07.21 └── release-crosshatch-2019.10.07.21 ├── crosshatch-factory-2019.10.07.21.zip ├── crosshatch-factory-2019.10.07.21.zip.sig ├── crosshatch-img-2019.10.07.21.zip ├── crosshatch-ota_update-2019.10.07.21.zip ├── crosshatch-target_files-2019.10.07.21.zip └── crosshatch-testing
Vanadium is a hardened fork of Chromium developed by GrapheneOS and used to provide the WebView and optionally the standalone browser app. It tracks the Chromium release cycles along with having additional updates for downstream changes to the privacy and security hardening patches, so it's updated at a different schedule than the monthly Android releases.
The browser and the WebView are independent applications built from the Chromium source tree. The GrapheneOS browser build is located at external/vanadium and the WebView is at external/chromium-webview.
See Chromium's Android build instructions for details on obtaining the prerequisites.
You can obtain the proper configuration from the
GrapheneOS Vanadium repository in
args.gn including the correct
git clone https://github.com/GrapheneOS/Vanadium.git cd Vanadium git checkout $CORRECT_BRANCH_OR_TAG
Fetch the Chromium sources:
fetch --nohooks android
Sync to the latest stable release for Android (replace $VERSION with the correct value):
gclient sync -D --with_branch_heads -r $VERSION --jobs 32
Apply the GrapheneOS patches on top of the tagged release:
cd src git am --whitespace=nowarn ../*.patch
Generate a signing key for Vanadium if this is the initial build (the sample
password configured in args.gn is
keytool -genkey -v -keystore vanadium.keystore -alias vanadiumkey -keyalg RSA -keysize 4096 -sigalg SHA512withRSA -validity 10000 -dname "cn=GrapheneOS"
You should back this up with your other keys.
Then, configure the build in the
gn args out/Default
Copy the GrapheneOS configuration from
../args.gn and save/exit the
target_cpu as needed if the target is not arm64. For
x86_64, the correct value for
x64, but note
that the Android source tree refers to it as x86_64.
To build ChromeModernPublic, which provides the browser app:
ninja -C out/Default/ chrome_modern_public_apk
The apk needs to be copied from
into the Android source tree at
external/vanadium/prebuilt/arm64/ChromeModernPublic.apk with arm64
substituted with the correct value for other architectures (arm, x86, x86_64).
To build SystemWebView, which provides the WebView:
ninja -C out/Default/ system_webview_apk
The apk needs to be copied from
into the Android source tree at
external/chromium-webview/prebuilt/arm64/webview.apk with arm64
substituted with the correct value for other architectures (arm, x86, x86_64).
Vanadium cannot yet provide the WebView for Android 10. The changes for this have not yet landed upstream for the current stable release. It either needs to be addressed upstream or downstream in order for this to work again.
WebView provider apps need to be whitelisted in
The official releases of the Auditor and PdfViewer apps are bundled as an apk into
external/ repositories. There are no modifications to these for GrapheneOS. These are
built and signed with the standard
gradle Android plugin build
It can be useful to set up a standalone installation of the SDK separate from the Android Open Source Project tree. This is how the prebuilt apps are built, rather than using the older branch of the SDK in the OS source tree.
Android Studio can also be set up to use an existing SDK and will recognize it and use it automatically if Android Studio is installed with an SDK installation already available and set up in the environment. You'll also likely want a working command-line SDK environment even if you do heavily use Android Studio.
Using the official releases of the SDK is recommended for simplicity, although with a lot of effort you can build everything yourself. Distribution packages are generally quite out-of-date and should be avoided. To set up a minimal SDK installation without Android Studio on Linux:
mkdir ~/sdk cd ~/sdk wget https://dl.google.com/android/repository/sdk-tools-linux-4333796.zip unzip sdk-tools-linux-4333796.zip rm sdk-tools-linux-4333796.zip
Add the directories to your PATH in your shell profile configuration and do the same in your current shell:
export PATH="$HOME/sdk/tools:$HOME/sdk/tools/bin:$HOME/sdk/platform-tools:$HOME/sdk/build-tools/29.0.2:$PATH:$HOME/sdk/ndk-bundle" export ANDROID_HOME="$HOME/sdk"
Run an initial update:
Install platform-tools for tools like adb and fastboot:
For running the Compatibility Test Suite you'll also need the build-tools for aapt:
For working with native code, you need the NDK:
You should update the sdk before use from this point onwards:
This section will be expanded to cover various test suites and testing procedures rather than only the current very minimal coverage of the Compatibility Test Suite (CTS).
To test a build for the emulator, run
emulator within the build
environment. The emulator will use CPU hardware acceleration via KVM along with
optional graphics acceleration via the host GPU if these are available.
Testing with the Compatibility Test Suite (CTS) can be done by either building the test suite from source or using the official releases.
Official releases of the CTS can be downloaded from the Compatibility Suite Downloads page. You should download the CTS for the relevant release (Android 9) and architecture (ARM). There's a separate zip for the main CTS, the manual portion (CTS Verifier) and the CTS for Instant Apps. The latest release of the CTS Media Files also needs to be downloaded from that section.
You'll need a device attached to your computer with ADB enabled along with the
Android SDK installed. The build-tools and platform-tools packages need to be
installed and the binaries need to be added to your PATH. For example, with the SDK
export ANDROID_HOME="$HOME/sdk" export PATH="$PATH:$HOME/sdk/tools:$HOME/sdk/tools/bin:$HOME/sdk/platform-tools:$HOME/sdk/build-tools/29.0.2:$HOME/sdk/ndk-bundle"
Copy media onto the device:
cd android-cts-media-1.4 ./copy_images.sh ./copy_media.sh
You also need to do some basic setup for the device. It's possible for changes from a baseline install to cause interference, so it can be a good idea to factory reset the device if assorted changes have been made. The device needs to be running a user build for the security model to be fully intact in order to pass all the security tests. A userdebug build is expected to fail some of the tests. GrapheneOS also makes various changes intentionally deviating from the requirements expected by the CTS, so there will always be some expected failures. A few of the tests are also known to be quite flaky or broken even with the stock OS and/or AOSP. These will be documented here at some point.
- Must be connected to a WiFi network with IPv6 internet access
- Must have a working SIM card with mobile data with IPv6 internet access
- Disable SIM lock
- Enable Bluetooth
- Enable NFC and NDEF (Android Beam)
- Open / close Chromium to deal with initial setup
- Prop up with a good object to focus on and good lighting for Camera tests
- Bluetooth beacons for Bluetooth tests
- Must have a great GPS/GNSS signal for location tests
- SIM card with carrier privilege rules
- Secure element applet installed on the embedded secure element or SIM card
- At least one Wi-Fi RTT access point powered up but not connected to any network
- The screen lock must be disabled.
Run the test harness:
_JAVA_OPTIONS being set will break the version detection.
To obtain a list of CTS modules:
To run a specific module and avoid wasting time capturing device information:
run cts --skip-device-info --module CtsModuleName
To speed up initialization after running some initial tests:
run cts --skip-device-info --skip-preconditions --module CtsModuleName
It's possible to run the whole standard CTS plan with a single command, but running specific modules is recommended, especially if you don't have everything set up for the entire test suite.
The following programming languages are acceptable for completely new GrapheneOS projects:
- Kotlin for apps and any services closely tied to the apps, now that it's not only officially supported by the Android SDK and Android Studio but also the default language with Kotlin exclusive enhancements to the APIs
- Rust with
no_stdfor low-level code used in a hypervisor, kernel, daemon, system library, etc. Keep in mind that low-level code is to be avoided whenever a higher language language is better suited to the job. In general, the project aims to avoid creating more low-level code manually dealing with memory ownership and lifetimes in the first place.
- C in rare cases for very small and particularly low-level projects without opportunities to reduce the trusted computing base for memory corruption to any significant degree with Rust, such as for the hardened_malloc project
- arm64 assembly in extremely rare cases where C or Rust aren't usable with compiler intrinsics
- Python 3 for small (less than 500 lines) development-related scripts that are not exposed to untrusted input. It's never acceptable to use it for client-side code on devices or for servers. It isn't used on the servers even for non-application-server code.
- Bash for tiny (less than 200 lines) build scripts without any non-trivial logic where Python would be an annoyance.
For existing projects, use the official upstream code style. Avoid using legacy conventions that they're moving away from themselves. Follow the code style they use for new additions. Some projects have different code styles for different directories or files depending on their sources, in which case respect the per-file style.
For new projects, follow the official code style for the language. Treat the
standard library APIs as defining the naming style for usage of the language, i.e. C
CONSTANT_NAME. For Python, follow PEP8 and the
same goes for other languages with official styles whether defined in a document or by
the default mode for the official formatting tool like
For cases where there isn't an official or prevailing code style for other things,
avoid tabs, use 4-space indents,
Prefer single-line comment syntax other than rare cases where it makes sense to add a
tiny comment within a line of code. In languages with the optional braces misfeature
(C, C++, Java), always use them. Open braces on the same line as function definitions
/ statements. Wrap lines at 100 columns except in rare cases where it would be far
uglier to wrap the line.
"use strict"; at the top of every file, end lines
with semicolons (since automatic insertion is poorly designed) and always use
const to declare variables, unless they are reassigned in which case they
should be declared with
let but never use
var as it is
effectively broken. Try to prefer loops with
For web content, use dashes as user-facing word separators rather than underscores. Page titles should follow the scheme "Page | Directory | Higher-level directory | Site" for usability with a traditional title as the Open Graph title.
Avoid designing around class inheritance unless it's a rare case where it's an extremely good fit or the language sucks (Java) and it's the least bad approach, but still try to avoid it.
Use concise but self-explanatory variable names. Prefer communicating information
via naming rather than using comments whenever possible. Don't name variables
k, etc. like C programmers. It's okay to
use things like
y for parameters if the function is
genuinely that generic and operates on arbitrary values. In general, try to scope
variables into the most limited scope (in C or C++, be careful about this when
references are taken).
Write code that's clean and self-explanatory. Use comments to explain or justify non-obvious things, but try to avoid needing them in the first place. In most cases, they should just be communicating non-local information such as explaining why an invariant is true based on the code elsewhere (consider a runtime check to make sure it's true, or an assertion if performance would be an issue). Docstrings at the top of top-level functions, modules, etc. are a different story and shouldn't be avoided.
Make extensive usage of well designed standard library modules. For apps, treat Jetpack (androidx) as part of the standard library and make good use of it. For Java, Guava can also be treated as part of the standard library.
Libraries outside of the standard library should be used very cautiously. They should be well maintained, stable, well tested and widely used. Libraries implemented with memory unsafe languages should generally be avoided (one exception: SQLite).
Generally, frameworks and libraries existing solely to provide different paradigms and coding patterns are to be avoided. They increase barrier to entry for developers, generally only increase complexity unless used at very large scales (and may not even make things simpler in those cases) and come and go as fads. This is only okay when it's part of the standard libraries or libraries that are considered standard (androidx, Guava) by GrapheneOS and should still be approached cautiously. Only use it if it truly makes the correct approach simpler. Ignore fads and figure out if it actually makes sense to use, otherwise just stick to the old fashioned way if the fancy alternatives aren't genuinely better.