A Mac OS X library for managing and manipulating iOS Simulators
Objective-C Swift Other
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Summary: Since these are `PrivateHeaders` only a header may be present. Instead of having our own code in this Framework, we can instead just have the enums declared.

Reviewed By: phyllipecesar

Differential Revision: D6765597

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Configuration Add Xcode 9 Default Compiler Warnings Oct 4, 2017
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FBSimulatorControl.xcodeproj Make AXRuntime Header-Only Jan 20, 2018
FBSimulatorControl Make AXRuntime Header-Only Jan 20, 2018
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Shims Don't allow builds of arm binaries Dec 7, 2017
XCTestBootstrap Task Starting Asynchrony Exposed Jan 19, 2018
XCTestBootstrapTests Fix many tests in FBSimulatorControlTestCase Nov 22, 2017
fbsimctl Use Future-Based Image Fetching in fbsimctl Jan 5, 2018
fbxctest Fix Test Breakage on Test Suite Counts Jan 8, 2018
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LICENSE Initial Commit πŸš€ Sep 10, 2015
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README.md Fix spelling. Oct 10, 2017
build.sh Testing the importer w/ some trivial changes Oct 9, 2017



A macOS library for managing, booting and interacting with multiple iOS Simulators simultaneously.

Build Status


  • Enables 'Multisim' for iOS: Booting of multiple Simulators on the same host OS.
  • Runs independently of Xcode and xcodebuild. Uses the toolchain defined by xcode-select.
  • Boots iPhone & iPad Simulators for iOS 8, 9 & 10.
  • Launches both 'Agent' and 'Application' processes, with Arguments and Environment.
  • Can boot Simulators via Xcode's Simulator.app or by launching 'Directly' in CoreSimulator.
  • 'Direct Launch' supports video recording, screenshot fetching & interfacing with the SimulatorBridge.
  • 'Diagnostic' API for fetching System, App & Crash logs as well as Screenshots & Video.
  • An 'Event Bus' that exposes the details of a Simulator's lifecycle including Applications, Agents & the Simulator itself.
  • NSNotifications interface for the 'Event Bus'.
  • Stateless by Default: Knowledge the current state of Simulators can be re-built when FBSimulatorControl is launched.
  • BFFs with WebDriverAgent.
  • No external dependencies.
  • A Pure Objective-C Framework, so as not to force a Swift-Version dependency.
  • An API designed with Swift in mind.


The original use-case for FBSimulatorControl was to boot Simulators to run End-to-End tests with WebDriverAgent. As FBSimulatorControl is a macOS framework, it can be linked to from inside any macOS Library, Application, or xctest target. There may be additional use-cases that you may find beyond UI Test Automation.

FBSimulatorControl works by linking with the private DVTFoundation, CoreSimulator and DVTiPhoneSimulatorRemoteClient frameworks that are present inside the Xcode bundle. Doing this allows FBSimulatorControl to talk directly to the same APIs that Xcode and simctl do. This, combined with launching the Simulator binaries directly, means that multiple Simulators can be launched simultaneously. Test targets can be made that don't depend on any Application targets, or that launch multiple Application targets. This enables running against pre-built and archived Application binaries, rather than a binary that is built by a Test Target.

As FBSimulatorControl nears a stable version, the API may change but can be considered mostly stable.


The fastest way to get a usable installation of the Framework is to install fbsimctl with homebrew. This will build the FBSimulatorFramework at the same time and install it to /usr/local/Cellar/fbsimctl/Frameworks by default.

The homebrew installation is derived from the build.sh script in this directory. You can build FBSimulatorControl with the following: build.sh framework build

The FBSimulatorControl.xcodeproj will build the FBSimulatorControl.framework and the FBSimulatorControlTests.xctest bundles without any additional dependencies. The Project File is checked into the repo and the Framework can be build from this project.

Once you build the FBSimulatorControl.framework, it can be linked like any other 3rd-party Framework for your project:

  • Add FBSimulatorControl.framework to the Target's 'Link Binary With Libraries' build phase.
  • Ensure that FBSimulatorControl is copied into the Target's bundle (if your Target is an Application or Framework) or a path relative to the Executable if your project does not have a bundle.


In order to support different Xcode versions and system environments, FBSimulatorControl weakly links against Xcode's Private Frameworks and load these Frameworks when they are needed. FBSimulatorControl will link against the version of Xcode that you have set with xcode-select. The Xcode version can be overridden by setting the DEVELOPER_DIR environment variable in the process that links with FBSimulatorControl.

Since the Frameworks upon which FBSimulatorControl depends are loaded lazily, they must be loaded before using the Framework. Any of the FBSimulatorControl classes that have this runtime dependency will load these Private Frameworks when they are used for the first time.

The tests should provide you with some basic guidance for using the API. FBSimulatorControl has an umbrella header that can be imported to give access to the entire API.

For a high level overview:

  • FBSimulatorControl is the Principal Class. It is the first object that you should create with +[FBSimulatorControl withConfiguration:error:]. It creates a FBSimulatorPool upon creation.
  • FBSimulatorSet wraps SimDeviceSet and provides a resiliant CRUD API for Deleting, Creating and Erasing Simulators.
  • FBSimulatorPool builds on FBSimulatorSet by providing an 'Allocation' API that allows Simulators to be reserved and re-used within the Framework.
  • FBSimulator is a reference type that represents an individual Simulator. It has a number of convenience methods for accessing information about a Simulator. Many of the possible actions you can perform on a Simulator are present on instances of this class.
  • FBSimulatorDiagnostics is a facade around available diagnostics for a Simulator. It fetches static logs such as the System Log on-demand and receives new logs from components such as FBFramebufferVideo.
  • Configuration objects: FBApplicationLaunchConfiguration, FBAgentLaunchConfiguration, FBSimulatorApplication, FBSimulatorControlConfiguration, FBSimulatorConfiguration & FBSimulatorBootConfiguration.

Since FBSimulatorControl is built as a Framework Module, it's easy to make Swift Scripts that use the Framework:

To launch Safari on an iPhone 6, you can run the following:

#!/usr/bin/env xcrun swift -F /usr/local/Frameworks
// The -F Argument should be the directory in which the FBSimulatorControl.framework is located.

// Import the FBSimulatorControl Framework
import FBSimulatorControl

// Create the FBSimulatorControl Instance.
let options = FBSimulatorManagementOptions()
let config = FBSimulatorControlConfiguration(deviceSetPath: nil, options: options)
let logger = FBControlCoreGlobalConfiguration.defaultLogger()
let control = try FBSimulatorControl.withConfiguration(config, logger: logger)

// Get an existing iPhone 6 from the Simulator Pool.
let simulator = try control.pool.allocateSimulator(
  with: FBSimulatorConfiguration.iPhone6(),
  options: FBSimulatorAllocationOptions.reuse
print("Using \(simulator)")

// If it is booted, keep it booted, otherwise boot it.
if (simulator.state != .booted) {
  print("Booting Simulator \(simulator)")
  try simulator.boot()

// List the Installed Apps and get the first installed app
let applications = simulator.installedApplications()
let application = applications.first!

// Launch the first installed Application
let appLaunch = FBApplicationLaunchConfiguration(
  application: application,
  arguments: [],
  environment: [:],
  output: FBProcessOutputConfiguration.outputToDevNull()
print("Launching \(application)")
try simulator.launchApplication(appLaunch)

FBSimulatorControl currently has two ways of launching Simulators that have tradeoffs for different use cases:


The CoreSimulator Framework that is used by the Simulator.app as well as Playgrounds & Interface Builder has long had the concept of custom 'Device Sets' which contain created Simulators. Multiple Device Sets can be used on the same host and are an effective way of ensuring that multiple processes using CoreSimulator don't collide into each other. 'Device Sets' are also beneficial for an automation use-case, as using a different set other than the 'Default' will ensure that these Simulators aren't polluted.

CoreSimulator itself is also capable of running multiple Simulators on the same host concurrently. You can see this for yourself by using the simctl commandline. Booting Simulators this way can be of somewhat limited utility without the output of the screen. FBSimulatorControl solves this problem in two different ways:

Launching via Simulator.app

Simulator.app is the macOS Application bundle with Xcode that you are probably familiar with for viewing and interacting with a Simulator. This Mac Application is the part of the Xcode Toolchain that you will be used to.

FBSimulatorControl can launch the Application Excutable directly, thereby allowing specific Simulators to be booted by UDID and Device Set. This can be done by overriding the Simulator.apps NSUserDefaults by passing them as Arguments to the Application Process. Once the Simulator has booted, it can be interacted with via CoreSimulator with commands such as installing Apps and launch executables.

However, this mode of operation does limit the amount that FBSimulatorControl can manipulate the Simulator, once the Simulator.app process has been launched. In particular it's not possible to execute custom code inside the Simulator Application process, which means that it's not possible to get video frames that the booted simulator passes back to the Simulator.app process.

Direct Launch

FBSimulatorControl also supports 'Direct Launching'. This means that the Simulator is booted from the FBSimulatorControl Framework. This gives increasing control over the operation of the Simulator, including fetching frames from the Framebuffer. This means that pixel-perfect videos and screenshots can be constructed from the Framebuffer. In addition, FBSimulatorControl can communicate to the SimulatorBridge process running on the Simulator over XPC.

Direct Launching does not currently support manipulation of the UI within the Simulator, so is much better suited to a use-case where the UI is manipulated by other means.


fbsimctl is a Command Line Interface for FBSimulatorControl API calls, so FBSimulatorControl functionality can be used without the need to integrate with the Framework. It is currently under development. As fbsimctl is under active development, the User Interface will be prone to change.


See the CONTRIBUTING file for how to help out. There's plenty to work on the issues!

Example Projects


FBSimulatorControl is BSD-licensed. We also provide an additional patent grant.