Using an Android Emulator

Always use x86 emulators. Although arm emulators exist, they are so slow that they are not worth your time.

Building for Emulation

You need to target the correct architecture via GN args:

target_cpu = "x86"

Creating an Emulator Image

By far the easiest way to set up emulator images is to use Android Studio. If you don't have an Android Studio project already, you can create a blank one to be able to reach the Virtual Device Manager screen.

Refer to: https://developer.android.com/studio/run/managing-avds.html

Where files live:

• System partition images are stored within the sdk directory.
• Emulator configs and data partition images are stored within ~/.android/avd/.

Choosing a Skin

Choose a skin with a small screen for better performance (unless you care about testing large screens).

Choosing an Image

Android Studio's image labels roughly translate to the following:

AVD “Target”	GMS?	Build Properties
Google Play	This has GMS	user/release-keys
Google APIs	This has GMS	userdebug/dev-keys
No label	AOSP image, does not have GMS	eng/test-keys

If you're not sure which to use, choose Google APIs.

Configuration

“Show Advanced Settings” > scroll down:

• Set internal storage to 4000MB (component builds are really big).
• Set SD card to 1000MB (our tests push a lot of files to /sdcard).

Known Issues

• Our test & installer scripts do not work with pre-MR1 Jelly Bean.
• Component builds do not work on pre-KitKat (due to the OS having a max number of shared libraries).
• Jelly Bean and KitKat images sometimes forget to mount /sdcard :(.
  • This causes tests to fail.
  • To ensure it's there: adb -s emulator-5554 shell mount (look for /sdcard)
  • Can often be fixed by editing ~/.android/avd/YOUR_DEVICE/config.ini.
    • Look for hw.sdCard=no and set it to yes

Cloning an Image

Running tests on two emulators is twice as fast as running on one. Rather than use the UI to create additional avds, you can clone an existing one via:

$ tools/android/emulator/clone_avd.py \
    --source-ini ~/.android/avd/EMULATOR_ID.ini \
    --dest-ini ~/.android/avd/EMULATOR_ID_CLONED.ini \
    --display-name "Cloned Emulator"

Starting an Emulator from the Command Line

Refer to: https://developer.android.com/studio/run/emulator-commandline.html.

Ctrl-C will gracefully close an emulator.

Basic Command Line Use

$ ~/Android/Sdk/emulator/emulator @EMULATOR_ID

Running a Headless Emulator

You can run an emulator without creating a window on your desktop (useful for ssh):

$ sudo apt-get install xvfb-run
$ xvfb-run ~/Android/Sdk/emulator/emulator -gpu off @EMULATOR_ID

Writable system partition

Unlike physical devices, an emulator's /system partition cannot be modified by default (even on rooted devices). If you need to do so (such as to remove a system app), you can start your emulator like so:

$ ~/Android/Sdk/emulator/emulator -writable-system @EMULATOR_ID

Remote Desktop

For better graphics performance, use virtualgl (Googlers, see http://go/virtualgl):

$ vglrun ~/Android/Sdk/emulator/emulator @EMULATOR_ID

Using an Emulator

• Emulators show up just like devices via adb devices
  • Device serials will look like “emulator-5554”, “emulator-5556”, etc.