# Demonstration: What "Shares the Host Kernel" Actually Looks Like

## OBSERVE

```
$ uname -r
5.15.0-real-host-kernel
$ docker run --rm alpine:3.19 uname -r
5.15.0-real-host-kernel
```

## HYPOTHESIS

Predict: would a real virtual machine show the SAME kernel version as its host, the way this
container just did?

## INSPECT

A real VM runs its OWN independent kernel — it would very likely show a DIFFERENT version (or
even a different OS entirely) than its host, because a VM virtualizes the hardware and boots a
complete, separate operating system on top of it.

## CHANGE

```
$ docker run --rm ubuntu:22.04 uname -r
5.15.0-real-host-kernel
```

Even a completely different container OS (`ubuntu` here, vs. `alpine` before) STILL reports the
exact same kernel version — because there's only ONE real kernel involved, the host's.

## VERIFY

This is the concrete, observable meaning of "containers share the host kernel": no matter what
container image you run, `uname -r` always reports the same real kernel underneath — this is
exactly why containers start in a fraction of a second (no separate kernel to boot) and exactly
the tradeoff the lesson named.

## Instructor Notes

**Demo goal:** Make "shares the host kernel" a concrete, checkable fact rather than an abstract
architectural claim.

**Approximate timing:** 8 minutes live.

**Common mistake to watch for:** assuming different container images run different kernels
because their USERSPACE (installed tools, package manager) looks completely different — the
kernel underneath is unified regardless.