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Using an Android Emulator

Always use x86 emulators (or x86_64 for testing 64-bit APKs). Although arm emulators exist, they are so slow that they are not worth your time.

[TOC]

Building for Emulation

You need to target the correct architecture via GN args:

target_cpu = "x86"  # or "x64" if you have an x86_64 emulator

Running an Emulator

Using Prebuilt CIPD packages

Chromium has a set of prebuilt images stored as CIPD packages. These are used by various builders to run tests on the emulator. Their configurations are currently stored in //tools/android/avd/proto.

File Builder
tools/android/avd/proto/generic_android23.textpb android-marshmallow-x86-rel
tools/android/avd/proto/generic_android28.textpb android-pie-x86-rel
tools/android/avd/proto/generic_playstore_android28.textpb android-pie-x86-rel

You can use these configuration files to run the same emulator images locally.

Prerequisite

  • Make sure KVM (Kernel-based Virtual Machine) is enabled. See this link from android studio for more details and instructions.

  • You need to have the permissions to use KVM. Use the following command to see if you are in group kvm:

      $ grep kvm /etc/group

    If your username is not shown in the group, add yourself to the group:

      $ sudo adduser $USER kvm
  $ newgrp kvm

Running via the test runner

The android test runner can run emulator instances on its own. In doing so, it starts the emulator instances, runs tests against them, and then shuts them down. This is how builders run the emulator.

Options

  • --avd-config

    To have the test runner run an emulator instance, use --avd-config:

      $ out/Debug/bin/run_base_unittests \
      --avd-config tools/android/avd/proto/generic_android28.textpb

  • --emulator-count

    The test runner will launch one instance by default. To have it run multiple instances, use --emulator-count:

      $ out/Debug/bin/run_base_unittests \
      --avd-config tools/android/avd/proto/generic_android28.textpb \
      --emulator-count 4

  • --emulator-window

    The test runner runs the emulator in headless mode by default. To have it run with a window, use --emulator-window:

      $ out/Debug/bin/run_base_unittests \
      --avd-config tools/android/avd/proto/generic_android28.textpb \
      --emulator-window

Running standalone

The test runner will set up and tear down the emulator on each invocation. To manage emulator lifetime independently, use tools/android/avd/avd.py.

Note: Before calling avd.py start, use avd.py install to install the emulator configuration you intend to use. Otherwise the emulator won't start correctly.

  $ tools/android/avd/avd.py install \
      --avd-config tools/android/avd/proto/generic_android28.textpb
Options

  • --avd-config

    This behaves the same as it does for the test runner.

      $ tools/android/avd/avd.py start \
      --avd-config tools/android/avd/proto/generic_android28.textpb

    Note: avd.py start will start an emulator instance and then terminate. To shut down the emulator, use adb emu stop.

  • --emulator-window

    Like the test runner, avd.py runs the emulator in headless mode by default. To have it run with a window, use --emulator-window:

      $ tools/android/avd/avd.py start \
      --avd-config tools/android/avd/proto/generic_android28.textpb \
      --emulator-window

  • --no-read-only

    avd.py runs the emulator in read-only mode by default. To run a modifiable emulator, use --no-read-only:

      $ tools/android/avd/avd.py start \
      --avd-config tools/android/avd/proto/generic_android28.textpb \
      --no-read-only

  • --debug-tags

    avd.py disables the emulator log by default. When this option is used, emulator log will be enabled. It is useful when the emulator cannot be launched correctly. See emulator -help-debug-tags for a full list of tags.

      $ tools/android/avd/avd.py start \
      --avd-config tools/android/avd/proto/generic_android28.textpb \
      --debug-tags init,snapshot

Using Your Own 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/.

Creating an Image

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" Virtual Device Configuration tab GMS? Build Properties
Google Play "Recommended" (the default tab) This has GMS user/release-keys
Google APIs "x86 Images" This has GMS userdebug/dev-keys
No label "x86 Images" AOSP image, does not have GMS eng/test-keys

*** promo Tip: if you're not sure which to use, choose Google APIs under the x86 Images tab in the Virtual Device Configuration wizard.

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

Starting an Emulator from the Command Line

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

*** promo Ctrl-C will gracefully close an emulator.

*** promo Tip: zsh users can add https://github.com/zsh-users/zsh-completions to provide tab completion for the emulator command line tool.

Basic Command Line Use

$ # List virtual devices that you've created:
$ ~/Android/Sdk/emulator/emulator -list-avds
$ # Start a named device:
$ ~/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):

$ ~/Android/Sdk/emulator/emulator -no-window @EMULATOR_ID
$ # This also works for new enough emulator builds:
$ ~/Android/Sdk/emulator/emulator-headless @EMULATOR_ID

Running Multiple Emulators

Tests are automatically sharded amongst available devices. If you run multiple emulators, then running test suites becomes much faster. Refer to the "Multiple AVD instances" section of these emulator release notes for more about how this works.

$ # Start 8 emulators. Press Ctrl-C to stop them all.
$ ( for i in $(seq 8); do ~/Android/Sdk/emulator/emulator @EMULATOR_ID -read-only & done; wait )
$ # Start 12 emulators. More than 10 requires disabling audio on some OS's. Reducing cores increases parallelism.
$ ( for i in $(seq 12); do ~/Android/Sdk/emulator/emulator @EMULATOR_ID -read-only -no-audio -cores 2 & done; wait )

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

Using an Emulator

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

Emulator pros and cons

Pros

  • Compiles are faster. Many physical devices are arm64, whereas emulators are typically x86 (32-bit). 64-bit builds may require 2 copies of the native library (32-bit and 64-bit), so compiling for an arm64 phone is ~twice as much work as for an emulator (for targets which support WebView).
  • APKs install faster. Since emulators run on your workstation, adb can push the APK onto the emulator without being bandwidth-constrained by USB.
  • Emulators can be nice for working remotely. Physical devices usually require scp or ssh port forwarding to copy the APK from your workstation and install on a local device. Emulators run on your workstation, so there's no ssh slow-down.

Cons

  • If you're investigating a hardware-specific bug report, you'll need a physical device with the actual hardware to repro that issue.
  • x86 emulators need a separate out directory, so building for both physical devices and emulators takes up more disk space (not a problem if you build exclusively for the emulator).
  • userdebug/eng emulators don't come with the Play Store installed, so you can't install third party applications. Sideloading is tricky, as not all third-party apps support x86.