Building the System

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

Note: If you're building Android 6.0 or later, please see Compiling with Jack for information on this new default toolchain.

Set up environment

Initialize the environment with the envsetup.sh 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/envsetup.sh

or

$ . build/envsetup.sh

Choose a Target

Choose which target to build with lunch. The exact configuration can be passed as an argument. For example, the following command:

$ lunch aosp_arm-eng

refers to a complete build for the emulator, with all debugging enabled.指的是一个完整的编译过程生成虚拟机，所有的调试启用

If run with no arguments lunch will prompt you to choose a target from the menu.如果不带参数的lunch，你可以选择从菜单中选择一个目标。

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:

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

Build the code

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 fla** on a device. Please note that you have already selected your build target with lunch, and it is unlikely at best to run on a different target than it was built for.

你能在虚拟机和刷机运行编译系统。请注意你已经选择了编译系统的版本，它不可能在不同版本手机上运行很好。

Flash a Device

To flash a device, you will need to use fastboot, which should be included in your path after a successful build. Place the device in fastboot mode either manually by holding the appropriate key combination at boot, or from the shell with

安装到设备，你需要运行fastboot，

$ adb reboot bootloader

Once the device is in fastboot mode, run

$ fastboot flashall -w

The -w option wipes the /data partition on the device; this is useful for your first time flashing a particular device but is otherwise unnecessary.

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

Emulate an Android Device

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

$ emulator

Using ccache

ccache is a compiler cache for C and C++ that can help make builds faster. In the root of the source tree, do the following:

$ export USE_CCACHE=1
$ export CCACHE_DIR=/<path_of_your_choice>/.ccache
$ prebuilts/misc/linux-x86/ccache/ccache -M 50G

The suggested cache size is 50-100G.

On Linux, you can watch ccache being used by doing the following:

$ watch -n1 -d prebuilts/misc/linux-x86/ccache/ccache -s

On Mac OS, you should replace linux-x86 with darwin-x86.

When using Ice Cream Sandwich (4.0.x) or older, you should replace prebuilts/misc with prebuilt.

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
    https://source.android.com/source/download.html
************************************************************

This may be caused by:

• Failing to install the correct JDK as specified in Initializing the Build Environment.

• 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 Initializing the Build Environment for 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 Initializing the Build Environment for 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.