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Fuchsia Emulator (FEMU)

Fuchsia can run under emulation using Fuchsia Emulator (FEMU).

Prebuilt FEMU

FEMU is downloaded by jiri as part of jiri update or jiri run-hooks.

FEMU is fetched into //prebuilt/third_party/aemu. You can run it using fx emu (see section "Run Fuchsia under FEMU").

Network setup

In order to enable FEMU to connect to the local update server, you need to set up a persistent TUN/TAP device used by FEMU to create emulator network interface in advance.

Linux network setup

On Linux, run the following commands to setup the device and interface:

sudo ip tuntap add dev qemu mode tap user $USER
sudo ifconfig qemu up

macOS network setup

macOS does not support TUN/TAP devices out of the box; however, there is a widely used set of kernel extensions called tuntaposx that allow macOS to create virtual network interfaces.

For macOS 10.9 (Mavericks) and 10.10 (Yosemite), install TunTap using this installation package.

For macOS 10.13 (High Sierra) and later versions, do the following:

  1. Install Homebrew:

    /bin/bash -c "$(curl -fsSL"
  2. Install TunTap:

    brew cask install tuntap

The installation of TunTap may fail at first. In that case, do the following:

  1. Open System Preferences.
  2. Open Security & Privacy and select theGeneral tab.
  3. Next to the System software from developer "Mattias Nissler" was blocked from loading. message, click Allow (see Apple's User-Approved Kernel Extension Loading for details).
  4. Run the install command again:

    brew cask install tuntap

After installing TunTap, run the following command:

sudo chown $USER /dev/tap0

Run Fuchsia under FEMU

Ensure that you have set up and built the Fuchsia product (this example uses workstation product). Currently only x64 boards are supported.

fx set workstation.x64 --release [--with=...]
fx build

Then run Fuchsia Emulator with ssh access:

fx emu -N

To exit FEMU, run dm poweroff in the FEMU terminal.

Run FEMU without GUI

If you don't need graphics or working under the remote workflow, you can run FEMU in headless mode by adding --headless argument to the fx emu command, for example:

fx emu -N --headless

Specify GPU used by FEMU

By default, FEMU tries using the host GPU automatically if it is available, and will fall back to software rendering using SwiftShader if host GPU is unavailable.

You can also add argument --host-gpu or --software-gpu to fx emu command to enforce FEMU to use a specific graphics device.

Develop remotely

There are multiple ways to develop Fuchsia remotely using FEMU, and all the workflow supports GPU acceleration without requiring GPU drivers and runtime on the local machine.

Remote Desktop

These instructions require remote access to the remote machine using remote desktop tools like Chrome Remote Desktop.

Follow general remote desktop instructions for logging in to your remote machine. Once logged in, follow standard Fuchsia development instructions for building Fuchsia, and use the following command to run Fuchsia in the emulator inside your remote desktop session:

fx emu

The emulator will use Swiftshader instead of real GPU hardware for GPU acceleration when running inside Chrome Remote Desktop. Performance will be worse than using real GPU hardware but the benefit is that it runs on any workstation.

fx emu-remote Command

These instructions work for local machines with macOS or Linux, and require SSH access to a Linux workstation that is already able to run FEMU.

On the terminal of your local machine, type the following to start the emulator with networking on remote workstation and have the output forwarded using WebRTC to a Chrome tab on local machine:

fx emu-remote <remote-hostname> -- -N

This by default uses software rendering and GPU acceleration is supported by using an existing X server on the remote machine with access to GPU hardware:

fx emu-remote --display :0 <remote-hostname> -- -N

Any arguments after “--” will be passed to the fx emu invocation on the remote machine.