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page.title=Building the System
@jd:body

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    <h2>In this document</h2>
    <ol id="auto-toc">
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The following instructions to build the Android source tree apply to all branches, including master. 

<h2 id="choosing-a-branch">Choosing a Branch</h2>
<p>Some of the requirements for your build environment are determined by which
version of the source code you plan to compile. See
<a href="build-numbers.html">Codenames, Tags, and Build Numbers</a> for a full listing of branches you may
choose from. You may also choose to download and build the latest source code
(called "master"), in which case you will simply omit the branch specification
when you initialize the repository.</p>
<p>Once you have selected a branch, follow the appropriate instructions below to
set up your build environment.</p>


<p>The basic sequence of build commands is as follows:</p>
<h2 id="initialize">Initialize</h2>
<p>Initialize the environment with the <code>envsetup.sh</code> script. Note
that replacing "source" with a single dot saves a few characters,
and the short form is more commonly used in documentation.</p>
<pre><code>$ source build/envsetup.sh
</code></pre>
<p>or</p>
<pre><code>$ . build/envsetup.sh
</code></pre>
<h2 id="choose-a-target">Choose a Target</h2>
<p>Choose which target to build with <code>lunch</code>.  The exact configuration can be passed as
an argument, e.g. </p>
<pre><code>$ lunch aosp_arm-eng
</code></pre>
<p>The example above refers to a complete build for the emulator, with all debugging enabled.</p>
<p>If run with no arguments <code>lunch</code> will prompt you to choose a target from the menu. </p>
<p>All build targets take the form BUILD-BUILDTYPE, where the BUILD is a codename
referring to the particular feature combination. Here's a partial list:</p>
<table>
<thead>
<tr>
<th>Build name</th>
<th>Device</th>
<th>Notes</th>
</tr>
</thead>
<tbody>
<tr>
<td>aosp_arm</td>
<td>ARM emulator</td>
<td>AOSP, fully configured with all languages, apps, input methods</td>
</tr>
<tr>
<td>aosp_maguro</td>
<td>maguro</td>
<td>AOSP, running on Galaxy Nexus GSM/HSPA+ ("maguro")</td>
</tr>
<tr>
<td>aosp_panda</td>
<td>panda</td>
<td>AOSP, running on PandaBoard ("panda")</td>
</tr>
</tbody>
</table>
<p>and the BUILDTYPE is one of the following:</p>
<table>
<thead>
<tr>
<th>Buildtype</th>
<th>Use</th>
</tr>
</thead>
<tbody>
<tr>
<td>user</td>
<td>limited access; suited for production</td>
</tr>
<tr>
<td>userdebug</td>
<td>like "user" but with root access and debuggability; preferred for debugging</td>
</tr>
<tr>
<td>eng</td>
<td>development configuration with additional debugging tools</td>
</tr>
</tbody>
</table>
<p>For more information about building for and running on actual hardware, see
<a href="building-devices.html">Building for Devices</a>.</p>
<h2 id="build-the-code">Build the Code</h2>
<p>Build everything with <code>make</code>. GNU make can handle parallel
tasks with a <code>-jN</code> 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. E.g. on a
dual-E5520 machine (2 CPUs, 4 cores per CPU, 2 threads per core),
the fastest builds are made with commands between <code>make -j16</code> and
<code>make -j32</code>.</p>
<pre><code>$ make -j4
</code></pre>
<h2 id="run-it">Run It!</h2>
<p>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 <code>lunch</code>, and it is unlikely at best to run on a different target than it was built for.</p>
<h3 id="flash-a-device">Flash a Device</h3>
<p>To flash a device, you will need to use <code>fastboot</code>, 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</p>
<pre><code>$ adb reboot bootloader
</code></pre>
<p>Once the device is in fastboot mode, run </p>
<pre><code>$ fastboot flashall -w
</code></pre>
<p>The <code>-w</code> option wipes the <code>/data</code> partition on the device; this is useful for your first time flashing a particular device, but is otherwise unnecessary.</p>
<p>For more information about building for and running on actual hardware, see
<a href="building-devices.html">Building for Devices.</a></p>
<h3 id="emulate-an-android-device">Emulate an Android Device</h3>
<p>The emulator is added to your path automatically by the build process. To run the emulator, type</p>
<pre><code>$ emulator
</code></pre>
<h2 id="using-ccache">Using ccache</h2>
<p>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:</p>
<pre><code>$ export USE_CCACHE=1
$ export CCACHE_DIR=/&lt;path_of_your_choice&gt;/.ccache
$ prebuilts/misc/linux-x86/ccache/ccache -M 50G
</code></pre>
<p>The suggested cache size is 50-100G.</p>
<p>You can watch ccache being used by doing the following:</p>
<pre><code>$ watch -n1 -d prebuilts/misc/linux-x86/ccache/ccache -s
</code></pre>
<p>On OSX, you should replace <code>linux-x86</code> with <code>darwin-x86</code>.</p>
<p>When using Ice Cream Sandwich (4.0.x) or older, you should replace
<code>prebuilts/misc</code> with <code>prebuilt</code>.</p>
<h2 id="troubleshooting-common-build-errors">Troubleshooting Common Build Errors</h2>
<h3 id="wrong-java-version">Wrong Java Version</h3>
<p>If you are attempting to build a version of Android inconsistent with your
version of Java, <code>make</code> will abort with a message such as</p>
<pre><code>************************************************************
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
************************************************************
</code></pre>
<p>This may be caused by:</p>
<ul>
<li>
<p>Failing to install the correct JDK as specified in <a href="initializing.html">Initializing the Build Environment</a>.</p>
</li>
<li>
<p>Another JDK previously installed appearing in your path. Prepend the correct JDK to the beginning of your PATH or remove the problematic JDK.</p>
</li>
</ul>
<h3 id="python-version-3">Python Version 3</h3>
<p>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:</p>
<pre><code>$ apt-get install python
</code></pre>
<h3 id="case-insensitive-filesystem">Case Insensitive Filesystem</h3>
<p>If you are building on an HFS filesystem on Mac OS X, you may encounter an error such as</p>
<pre><code>************************************************************
You are building on a case-insensitive filesystem.
Please move your source tree to a case-sensitive filesystem.
************************************************************
</code></pre>
<p>Please follow the instructions in <a href="initializing.html">Initializing the Build Environment</a> for creating a case-sensitive disk image.</p>
<h3 id="no-usb-permission">No USB Permission</h3>
<p>On most Linux systems, unprivileged users cannot access USB ports by default. If you see a permission denied error, follow the instructions
<a href="initializing.html">Initializing the Build Environment</a> for configuring USB access.  </p>
<p>If adb was already running and cannot connect to the device after
getting those rules set up, it can be killed with <code>adb kill-server</code>.
That will cause adb to restart with the new configuration.</p>