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World D6: Under the Hood

Why Mac and Windows need a Linux VM

You will learn: why Docker Desktop runs a small Linux VM, and what that changes for you.

Checked with Docker Engine 29 on 31 Oct 2026

The problem

Aina runs nginx in Docker Desktop on her Mac. She types ps aux on the Mac. nginx is not in the list! Why?

Watch

zsh
docker version --format '{{.Client.Os}} / {{.Server.Os}}'
darwin / linux

Containers borrow a Linux kernel, and macOS has a different one. So Docker Desktop starts a small Linux VM (Docker Desktop): The small Linux computer Docker Desktop runs on a Mac or PC, because containers need a Linux kernel.. The engine lives there.

Try it

Where does the container’s process really run? Sort each setup.

Drag a card into a box. Or tap the card, then tap the box.

      Predict

      Your Mac has 16 GB. Docker Desktop’s VM is set to 4 GB. A container wants 6 GB. What happens?

      Check

      Your laptop~

      Lunchboxes (containers)

      • webrunning
        from nginx:1.30-alpine 8080→80

      Frozen packs (images)

      • nginx:1.30-alpine8 layers · 93.5MB · in use

      This practice laptop runs Linux, so both OS/Arch lines say linux. On a Mac, the Client line says darwin. The Server line still says linux.

      Check

      Put a Mac’s docker run -p 8080:80 in order, first at the top.

      First step at the top. Put these in order. Use the arrows, or drag.

      • You type docker run in the Mac terminal
      • Docker Desktop passes localhost:8080 from the Mac to the box
      • The docker command sends the order into the VM
      • nginx runs as a Linux process in the VM
      • dockerd in the Linux VM takes it
      • containerd and runc start the box

      You did it!

      You can now explain why Docker Desktop needs a Linux VM.

      Go deeper (optional)

      Where the story breaks, for all of Part 1: a real lunchbox has walls. A container has blinkers and portions on one shared stove. A kernel bug can reach every box at once. And meal packs are copied, but image layers are shared, never copied.

      Real rep (optional): peek at the hidden kitchen.

      Real mission

      1. docker version
      2. docker info

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