Building Android

The following instructions to build the Android source tree apply to all branches, including master. The basic sequence of build commands is as follows.

Set up environment

Initialize the environment with the script. Note that replacing source with . (a single dot) saves a few characters, and the short form is more commonly used in documentation.

source build/


. build/

To see a list of available commands in the build environment, run:


Choose a target

Choose which target to build with lunch. 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 will prompt you to choose a target from the menu. See Selecting a device build for the build configurations of all existing devices.

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

Buildtype Use
user limited access; suited for production
userdebug like user but with root access and debuggability; preferred for debugging
eng development configuration with additional debugging tools

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 user testing with greater diagnosis capabilities. When developing with the userdebug build, you should 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 provide a good user experience. Otherwise, the eng build behaves similar to the user and userdebug builds so that device developers can see how the code behaves in those environments.

For more information about building for and running on actual hardware, see Running Builds.

Build the code

This section is merely a summary to ensure setup is complete. See Running Builds for detailed instructions on building Android.

Build everything with make. GNU make can handle parallel tasks with a -jN argument, and it's common to use a number of tasks N that's between 1 and 2 times the number of hardware threads on the computer being used for the build. For example, on a dual-E5520 machine (2 CPUs, 4 cores per CPU, 2 threads per core), the fastest builds are made with commands between make -j16 and make -j32.

make -j4

Run it!

You can either run your build on an emulator or flash it on a device. Please note that you have already selected your build target with lunch, and it is unlikely to run on a different target than it was built for.

Flash with fastboot

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

Emulate an Android device

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


Troubleshooting common build errors

Wrong Java version

If you are attempting to build a version of Android inconsistent with your version of Java, make will abort 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:

  • Failing to install the correct JDK as specified in JDK Requirements. Make sure you have followed the steps in Set up environment and Choose 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.

Python version 3

Repo is built on particular functionality from Python 2.x and is unfortunately incompatible with Python 3. In order to use repo, please install Python 2.x:

apt-get install python

Case insensitive filesystem

If you are building on an HFS filesystem on Mac OS, you may encounter an error such as

You are building on a case-insensitive filesystem.
Please move your source tree to a case-sensitive filesystem.

Please follow the instructions in Creating a case-sensitive disk image.

No USB permission

On most Linux systems, unprivileged users cannot access USB ports by default. If you see a permission denied error, follow the instructions in Configuring USB access.

If adb was already running and cannot connect to the device after getting those rules set up, it can be killed with adb kill-server. That will cause adb to restart with the new configuration.