Table of contents

Build targets

Smartphone targets:

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.

Generic targets:

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.

Board targets:

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.

Build dependencies

Downloading source code

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.

Development branch

The 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 -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 succeed.

Stable release

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 -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.

Updating and switching branches or tags

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:

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 automatically by 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
./ blueline

The kernel/google/wahoo repository is for the Pixel 2 and Pixel 2 XL and the kernel/google/crosshatch repository is for the Pixel 3, Pixel 3 XL, Pixel 3a and Pixel 3a XL.

Setting up the OS build environment

The build has to be done from bash as is not compatible with other shells like zsh.

Set up the build environment:

source script/

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 user with userdebug in order to have better debugging support. Production builds should be user builds as they are significantly more secure and don't make additional performance sacrifices to improve debugging.

Reproducible builds

To reproduce a past build, you need to export BUILD_DATETIME and BUILD_NUMBER to the values set for the past build. These can be obtained from out/build_date.txt and out/build_number.txt in a build output directory and the and 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.

Extracting vendor files for Pixel devices

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/ -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 passed with --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.

Faster builds for development use only

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:

make -j20

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.

Generating release signing 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 ../..

The 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.

Upgrading to Android 10

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/'

Enabling updatable APEX components

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 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.

Generating signed factory images and full update packages

Build the tool needed to generate A/B updates:

make -j20 brillo_update_payload

Generate a signed release build with the script:

script/ crosshatch

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 target_files zip.

Generating delta updates

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/ 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/ crosshatch 2019.09.25.00 2019.10.07.21

The script assumes that the releases are organized in the following directory structure:

├── 2019.09.25.00
│   └── release-crosshatch-2019.09.25.00
│       ├──
│       ├──
│       ├──
│       ├──
│       ├──
│       └── crosshatch-testing
└── 2019.10.07.21
    └── release-crosshatch-2019.10.07.21
        └── crosshatch-testing

Prebuilt code

Like the Android Open Source Project, GrapheneOS contains some code that's built separately and then bundled into the source tree as binaries. This section will be gradually expanded to cover building all of it.

Browser and WebView

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 including the correct version.

git clone
cd Vanadium

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 is vanadiumpass):

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 src directory:

gn args out/Default

Copy the GrapheneOS configuration from ../ and save/exit the editor. Modify target_cpu as needed if the target is not arm64. For x86_64, the correct value for target_cpu is 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 out/Default/apks/ChromeModernPublic.apk 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 out/Default/apks/SystemWebView.apk 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 frameworks/base/core/res/res/xml/config_webview_packages.

Prebuilt apps

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 system.

Standalone SDK

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

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:

sdkmanager --update

Install platform-tools for tools like adb and fastboot:

sdkmanager platform-tools

For running the Compatibility Test Suite you'll also need the build-tools for aapt:

sdkmanager 'build-tools;29.0.2'

For working with native code, you need the NDK:

sdkmanager ndk-bundle

You should update the sdk before use from this point onwards:

sdkmanager --update


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.

Compatibility Test Suite


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 located at /home/username:

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

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.

Run modules

Run the test harness:


Note that _JAVA_OPTIONS being set will break the version detection.

To obtain a list of CTS modules:

list 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.

Development guidelines

Programming languages

The following programming languages are acceptable for completely new GrapheneOS projects:

Much of the work is done on existing projects, and the existing languages should be used unless there are already clear stable API boundaries where a different language could be used without causing a substantial maintenance burden. The following languages are typical from most to least common: Java, C++, C, JavaScript, arm64 assembly, POSIX shell, Bash.

Code style

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 uses variable_or_function_name, type_name, MACRO_NAME while JavaScript uses variable_or_function_name, ClassName and 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 rustfmt.

For cases where there isn't an official or prevailing code style for other things, avoid tabs, use 4-space indents, function_name, variable_name, TypeName and CONSTANT_NAME. 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.

For JavaScript, put "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..of.

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 i, j, k, etc. like C programmers. It's okay to use things like x and 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.

Library usage

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.