FEX Emulator Docker Image

A minimal, optimized Docker image for running x86 and x86_64 programs on ARM64 systems using FEX-Emu.

Get it from DockerHub: https://hub.docker.com/r/stevenlafl/fex

What is FEX?

FEX allows you to run x86 applications on ARM64 Linux devices, similar to qemu-user and box64. It offers broad compatibility with both 32-bit and 64-bit x86 binaries, and it can be used alongside Wine/Proton to play Windows games.

Key Features

• API Forwarding: Forwards API calls to host system libraries (OpenGL, Vulkan) to reduce emulation overhead
• Code Cache: Experimental code cache minimizes in-game stuttering
• Per-App Configuration: Tweak performance per application (e.g., skip costly memory model emulation)
• FEXConfig GUI: User-friendly interface to explore and change emulation settings
• Broad Compatibility: Supports both 32-bit and 64-bit x86 binaries

What's Included

• FEX-Emu: x86/x86_64 emulator for ARM64 with binfmt support
• FEX RootFS: Ubuntu 24.04 x86_64 root filesystem (SquashFS, ~843MB)
• Ubuntu 24.04 ARM64: Minimal base image for ARM64 hosts

Image Size

Optimized using multi-stage builds and minimal dependencies:

• Content Size: ~1.05GB
• Disk Usage: ~2.53GB

Quick Start

Using Docker Compose (Recommended)

docker-compose up -d
docker exec -it fex-emulator /bin/bash

Using Pre-built Image

docker pull stevenlafl/fex:latest
docker run -it --rm stevenlafl/fex:latest

Build from Source

docker build -t stevenlafl/fex:latest .

Usage

Interactive Shell

The container starts with FEXBash by default, providing an x86 emulated environment:

docker run -it --rm stevenlafl/fex:latest

Running x86/x86_64 Binaries

# Inside FEXBash (default), binaries run automatically in emulated environment:
docker run -it --rm -v /path/to/x86/app:/app stevenlafl/fex:latest
cd /app && ./your-x86-binary

# To run a specific binary directly, use FEX:
docker run -it --rm -v /path/to/x86/app:/app stevenlafl/fex:latest FEX /app/your-x86-binary

Optimization Details

This Dockerfile is optimized for minimal image size:

1. Multi-stage build - Build dependencies don't bloat final image
2. --no-install-recommends - Prevents unnecessary package suggestions
3. Layer cleanup - Aggressive removal of apt cache, temp files
4. Auto-remove dependencies - Purges build tools after use
5. SquashFS RootFS - 577MB smaller than EROFS format

Technical Details

FEX Executables

The image includes several FEX utilities:

• FEX - Main emulator executable for running x86/x86_64 programs

  FEX /path/to/x86-binary

• FEXInterpreter - Deprecated alias for FEX (backwards compatibility)

• FEXConfig - Qt-based GUI for configuring emulation settings

• FEXBash - Starts a bash instance running under emulation

  FEXBash

  Note: This is not a chroot! Don't use sudo inside this environment.

• FEXMountDaemon - Background mount daemon for SquashFS-based rootfs

  • Usually one instance runs at a time
  • Closes when FEX exits (with 10-second timeout window)
  • Automatically managed; manual intervention rarely needed

FEX RootFS

The image uses the official FEX Ubuntu 24.04 x86_64 RootFS:

• Type: SquashFS (compressed filesystem)
• Location: ~/.fex-emu/RootFS/Ubuntu_24_04.sqsh
• Source: https://rootfs.fex-emu.gg/
• Purpose: Provides x86_64 system libraries for emulated binaries

Binfmt Support

The image includes fex-emu-binfmt32 and fex-emu-binfmt64 for transparent x86/x86_64 binary execution on ARM64 hosts.

License

This Docker configuration is provided as-is. FEX-Emu and included components have their own licenses.

Links

• FEX-Emu Official Site
• FEX-Emu GitHub
• FEX RootFS Repository