# What Is the Difference between CMD and ENTRYPOINT in a Dockerfile?

There is a big confusion around similarity and lack of clarity in the difference between the `CMD` and `ENTRYPOINT` instruction in Docker. Let’s clear things up.

## See the example

Let’s say we want to create a new Ubuntu image whose only purpose is to sleep for a while. The Dockerfile would look something like this:

```bash
FROM ubuntu
CMD sleep 10
```

And we would build and run the image like this:

```bash
docker build -t docker_sleep .
docker run docker_sleep
# sleep for 10 seconds
```

Just like this, we have executed the `CMD` instruction. But what actually happened under the hood is that the `sleep 10` command was passed to the `/bin/sh -c` which is the default Linux shell, therefore the command was executed. But why is that, you may ask. This is because the default `ENTRYPOINT` is set to the `/bin/sh -c` and the `sleep 10` is only the argument that is passed to the `ENTRYPOINT`.

If we were to build the image from the following Dockerfile:

```bash
FROM ubuntu
ENTRYPOINT sleep
```

And build run it like this:

```bash
docker run custom_sleep 20
```

It would do exactly the same as last time. Why is that, you may as again. This is because we have specified the `ENTRYPOINT` as `sleep` and the argument for the `ENTRYPOINT` as `20`.

## The difference

**The `ENTRYPOINT` is the program that is going to be run and the `CMD` is the argument that is going to be passed to that program**. Arguments passed to the container when running `docker run <container>` are in fact `CMD` and are passed to the `ENTRYPOINT`. Default `ENTRYPOINT` is set to the default Linux shell.