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    <h2>In this document</h2>
    <ol id="auto-toc">
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<p>The following instructions to build the Android source tree apply to all
branches, including <code>master</code>. The basic sequence of build commands
is as follows:</p>

<p class="note"><strong>Note:</strong> If you're building Android 6.0 or later,
please see <a href="jack.html">Compiling with Jack</a> for information on this
new default toolchain.</p>

<h2 id="obtaining-proprietary-binaries">Obtain proprietary binaries</h2>

<p>AOSP cannot be used from pure source code only and requires additional
hardware-related proprietary libraries to run, such as for hardware
graphics acceleration. See the sections below for download links and <a
href="requirements.html#binaries">Device binaries requirements</a> for
additional resources.</p>

<h3 id="downloading-proprietary-binaries">Download proprietary binaries</h3>

<p>You can download official binaries for the supported devices running tagged
AOSP release branches from <a
href="https://developers.google.com/android/nexus/drivers">Google's Nexus
driver page</a>. These binaries add access to additional hardware capabilities
with non-open source code. To instead build the AOSP master branch, use the
<a href="https://developers.google.com/android/nexus/blobs-preview">Binaries
Preview for Nexus Devices</a>. When building the master branch for a device, use
the binaries for the <a href="{@docRoot}source/build-numbers.html">most recent
numbered release</a> or with the most recent date.</p>

<h3 id="extracting-proprietary-binaries">Extract proprietary binaries</h3>

<p>Each set of binaries comes as a self-extracting script in a compressed
archive. Uncompress each archive, run the included self-extracting script from
the root of the source tree, then confirm that you agree to the terms
of the enclosed license agreement. The binaries and their matching makefiles
will be installed in the <code>vendor/</code> hierarchy of the source tree.</p>

<h3 id="cleaning-up">Clean up</h3>

<p>To ensure the newly installed binaries are properly taken into account after
being extracted, delete the existing output of any previous build using:</p>
<pre><code>$ make clobber
</code></pre>

<h2 id="initialize">Set up environment</h2>
<p>Initialize the environment with the <code>envsetup.sh</code> script. Note
that replacing <code>source</code> with <code>.</code> (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. For example, the following command:</p>
<pre><code>$ lunch aosp_arm-eng
</code></pre>
<p>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 <code>BUILD-BUILDTYPE</code>, where the
<code>BUILD</code> is a codename referring to the particular feature combination.</p>

<p>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="running.html">Running Builds</a>.</p>

<h2 id="build-the-code">Build the code</h2>

<p>Please note, this section is merely a summary to ensure setup is complete. See
<a href="running.html">Running Builds</a> for detailed instructions on building
Android.</p>

<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. 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 <code>make -j16</code> and
<code>make -j32</code>.</p>

<pre>
$ make -j4
</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>

<p class="note"><strong>Note:</strong> Remember to <a
href="#obtaining-proprietary-binaries">obtain proprietary binaries</a> or your
build will not boot successfully on your target hardware. If you obtain binary
blobs at this point you will need to unpack them, <code>make clobber</code> and
rebuild.</p>

<h3 id="flash-a-device">Flash with fastboot</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. See <a
href="running.html#flashing-a-device">Flashing a device</a> for
instructions.</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>
$ emulator
</pre>

<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>
************************************************************
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/initializing.html
************************************************************
</pre>

<p>This may be caused by:</p>

<ul>
<li>Failing to install the correct JDK as specified in <a
href="requirements.html#jdk">JDK Requirements</a>.</li>
<li>Another JDK previously installed appearing in your path. Prepend the
correct JDK to the beginning of your PATH or remove the problematic JDK.</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>
$ apt-get install python
</pre>

<h3 id="case-insensitive-filesystem">Case Insensitive Filesystem</h3>

<p>If you are building on an HFS filesystem on Mac OS, you may encounter an error such as</p>
<pre>
************************************************************
You are building on a case-insensitive filesystem.
Please move your source tree to a case-sensitive filesystem.
************************************************************
</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>