How to fix exec format error (using QEMU emulation) in Docker

# On Ubuntu/Debian
sudo apt-get update
sudo apt-get install -y qemu qemu-user-static binfmt-support

# On Fedora/CentOS/RHEL
sudo dnf install qemu-user-static

# On Arch Linux
sudo pacman -S qemu-user-static qemu-user-static-binfmt

# Check for registered handlers
ls /proc/sys/fs/binfmt_misc/

# You should see entries like qemu-aarch64, qemu-arm, etc.

# Register all QEMU handlers with persistent mode
docker run --rm --privileged multiarch/qemu-user-static --reset -p yes

# Verify it worked by running an ARM container on x86
docker run --rm arm64v8/alpine uname -m
# Should output: aarch64

# Or x86 on ARM
docker run --rm amd64/alpine uname -m
# Should output: x86_64

# Create and use a new builder with multi-platform support
docker buildx create --name mybuilder --use --bootstrap

# Verify QEMU platforms are available
docker buildx inspect --bootstrap
# Should show platforms like: linux/amd64, linux/arm64, linux/arm/v7, etc.

# Build for a specific platform
docker buildx build --platform linux/arm64 -t myimage:arm64 .

# Build multi-platform image
docker buildx build --platform linux/amd64,linux/arm64 -t myimage:latest --push .

# Run ARM container on x86 with explicit platform
docker run --platform linux/arm64 arm64v8/ubuntu:22.04 uname -m

# Run x86 container on ARM (e.g., Apple Silicon)
docker run --platform linux/amd64 ubuntu:22.04 uname -m

# Pull with specific platform
docker pull --platform linux/arm64 nginx:latest

export DOCKER_DEFAULT_PLATFORM=linux/amd64
docker run ubuntu:22.04 uname -m  # Will use amd64

# Check for Windows line endings (CRLF)
file your-script.sh
# Bad: "your-script.sh: ASCII text, with CRLF line terminators"
# Good: "your-script.sh: ASCII text"

# Convert to Unix line endings
sed -i 's/\r$//' your-script.sh
# Or use dos2unix
dos2unix your-script.sh

# Copy and fix line endings
COPY entrypoint.sh /entrypoint.sh
RUN sed -i 's/\r$//' /entrypoint.sh && chmod +x /entrypoint.sh

#!/bin/bash  # Requires bash to be installed
#!/bin/sh   # More portable, works on Alpine
#!/usr/bin/env python3  # For Python scripts

# Inspect local image architecture
docker image inspect myimage:latest --format '{{.Os}}/{{.Architecture}}'

# Check remote image platforms
docker buildx imagetools inspect nginx:latest
# Shows all available platforms in the manifest

# Check your host architecture
uname -m
# x86_64 = linux/amd64
# aarch64 = linux/arm64
# armv7l = linux/arm/v7

name: Build Multi-Arch
on: [push]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      # Required for cross-platform builds
      - name: Set up QEMU
        uses: docker/setup-qemu-action@v3

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Build and push
        uses: docker/build-push-action@v5
        with:
          context: .
          platforms: linux/amd64,linux/arm64
          push: true
          tags: user/app:latest

# Restart Docker daemon
sudo systemctl restart docker

# Re-register QEMU handlers
docker run --rm --privileged multiarch/qemu-user-static --reset -p yes

# On Docker Desktop, restart via the GUI or:
# macOS
killall Docker && open -a Docker

# Windows (PowerShell as Admin)
Restart-Service docker

sudo systemctl status binfmt-support
sudo systemctl restart binfmt-support