Building Android

Follow these instructions to begin building Android.

Setting up the environment

Initialize the environment with the script:

source build/


. build/

See the script at platform/build/ for descriptions of related commands, including lunch for selecting device targets and tapas for building unbundled apps, such as the reference TV app.

You need to reissue this command after every repo sync to pick up any changes to that script. Note that replacing source with . (a single dot) saves a few characters, and the short form is more commonly used in documentation.

The script imports several commands that enable you to work with the Android source code, including the commands used in this exercise.

To see the full list of available commands, run:


Choosing a target


Choose which target to build with lunch. lunch product_name-build_variant selects product_name as the product to build, and build_variant as the variant to build, and stores those selections in the environment to be read by subsequent invocations of m and other similar commands.

The exact configuration can be passed as an argument. For example, the following command refers to a complete build for the emulator, with all debugging enabled:

lunch aosp_arm-eng

If run with no arguments, lunch prompts you to choose a target from the menu, but note that the menu doesn't include every possibility. See Selecting a device build for the build configurations of all devices supported in AOSP, or talk to people on your team about the correct lunch for the device you're working on.

All build targets take the form BUILD-BUILDTYPE, where BUILD is a codename referring to the particular feature combination. BUILDTYPE is one of the following.

Buildtype Use
user Limited access; suited for production
userdebug Like user but with root access and debug capability; very close to production performance
eng Development configuration with faster build time; most suited for day-to-day development

The userdebug build should behave the same as the user build, with the ability to enable additional debugging that normally violates the security model of the platform. This makes the userdebug build good for understanding the performance and power used by the release. When developing with the userdebug build, follow the userdebug guidelines.

The eng build prioritizes engineering productivity for engineers who work on the platform. The eng build turns off various optimizations used to maximize runtime performance. Otherwise, the eng build is very similar to the user and userdebug builds so that device developers can see how the code behaves in those environments.

To see the current lunch settings, run the command:


For more information about building for and running on actual hardware, see Flashing Devices.


The tapas command configures the build of unbundled apps. It selects individual apps to be built by the Android build system. Unlike lunch, tapas does not request the building of images for a device.

Run tapas help for more information on the command.

Building the code

This section is a quick summary to ensure that setup is complete.

Build everything with m. m can handle parallel tasks with a -jN argument. If you don't provide a -j argument, the build system automatically selects a parallel task count that it thinks is optimal for your system.


As explained above, you can build specific modules instead of the full device image by listing their names in your m command line. In addition, m provides some pseudotargets for special purposes. Some examples are:

  • droid - m droid is the normal build. This target is here because the default target requires a name.
  • all - m all builds everything that m droid does, plus everything that doesn't have the droid tag. The build server runs this to make sure that everything that is in the tree and has an file builds.
  • m - Runs builds from the top of the tree. This is useful because you can run make from within subdirectories. If you have the TOP environment variable set, it uses that. If you don't, it looks up the tree from the current directory, trying to find the top of the tree. You can either build the whole source code tree by running m without arguments or build specific targets by specifying their names.
  • mma - Builds all of the modules in the current directory, and their dependencies.
  • mmma - Builds all of the modules in the supplied directories, and their dependencies.
  • croot - cd to the top of the tree.
  • clean - m clean deletes all of the output and intermediate files for this configuration. This is the same as rm -rf out/.

Run m help to see what other pseudotargets m provides.

Running the build

You can either run your build on an emulator or flash it on a device. Because you've already selected your build target with lunch, it's unlikely to run on a different target than it was built for.

Flashing with fastboot

To flash a device, use fastboot, which should be included in your path after a successful build. See Flashing a device for instructions.

Emulating an Android device

The emulator is added to your path automatically by the build process. To run the emulator, type:


Understanding build fingerprints

To track and report issues tied to a particular Android build, it is important to understand the build fingerprint. The build fingerprint is a unique, human-readable string containing manufacturer information issued to each build. See the FINGERPRINT description within the Build Parameters section of the Android Compatibility Definition Document (CDD) for the precise syntax.

The build fingerprint represents a particular Android implementation and revision. This unique key allows app developers and others to report issues with specific firmware versions. See Reporting bugs for the Android issue-reporting process.

A build fingerprint encapsulates all Android implementation details:

  • APIs: Android and native, as well as soft API behaviors
  • Core API and some system UI behavior
  • Compatibiility and security requirements defined in the CDD
  • Product specifications and the uses-feature setting employed by apps to target devices meeting expected requirements
  • Implementations of hardware and software components

See the CDD for complete details and Adding a New Device for instructions on creating an entirely new Android device.

Troubleshooting common build errors

Wrong Java version

If you're attempting to build a version of Android that's inconsistent with your version of Java, make aborts with a message such as:

You are attempting to build with the incorrect version
of java.

Your version is: WRONG_VERSION.
The correct version is: RIGHT_VERSION.

Please follow the machine setup instructions at

Here are the likely causes and solutions:

  • Failure to install the correct JDK as specified in the JDK requirements. Make sure you've followed the steps in Setting up the environment and Choosing a target.
  • Another JDK previously installed appearing in your path. Prepend the correct JDK to the beginning of your path or remove the problematic JDK.

No USB permission

By default on most Linux systems, unprivileged users can't access USB ports. If you see a permission denied error, follow the instructions in Configuring USB access.

If ADB was already running and can't connect to the device after getting those rules set up, you can kill it with adb kill-server. That command causes ADB to restart with the new configuration.