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World D6: Under the Hood

A container is just a process

You will learn: that a running container is a normal Linux process, and how to see it from both sides.

Checked with Docker Engine 29 on 31 Oct 2026

The problem

You run ps aux on your Linux laptop. One line says nginx: master process. But you never installed nginx! Where did it come from?

Watch

Your laptop~

Lunchboxes (containers)

  • webrunning
    from nginx:1.30-alpine 8080→80

Frozen packs (images)

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

docker top web asks Docker what runs in the lunchbox. ps aux asks the laptop. The PIDs match! The lunchbox is a normal process wearing blinkers.

Try it

Now look from inside the lunchbox. Type docker exec web ps.

Your laptop~

Lunchboxes (containers)

  • webrunning
    from nginx:1.30-alpine 8080→80

Frozen packs (images)

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

Predict

Inside, nginx is PID 1. On the laptop, it has a big PID. How many nginx masters are running?

Watch

Your laptop~

Lunchboxes (containers)

  • webrunning
    from nginx:1.30-alpine 8080→80

Frozen packs (images)

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

Both print the same kernel: The kitchen's one stove: the core of Linux. Every container on a machine cooks on the same kernel. version. The kernel is the kitchen’s one stove. Every lunchbox cooks on the laptop’s stove.

Check

Which ones are true for a container? Which ones fit a virtual machine?

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

      You did it!

      You can now show that a container is a process on your laptop.

      Go deeper (optional)

      On a Mac or Windows PC with Docker Desktop, ps won’t show nginx. It runs inside a small Linux VM (lesson 7).

      Real rep (optional, Linux): see one process from both sides.

      Real mission

      1. docker run -d --name web nginx:1.30-alpine
      2. docker top web
      3. ps -ef | grep nginx
      4. docker rm -f web

      0 of 4 steps done · Your ticks are saved.