moby/docs/sources/examples/hello_world_daemon.rst

:title: Hello world daemon example
:description: A simple hello world daemon example with Docker
:keywords: docker, example, hello world, daemon

.. _hello_world_daemon:

Hello World Daemon
==================
The most boring daemon ever written.

This example assumes you have Docker installed and with the base image already imported ``docker pull base``.
We will use the base image to run a simple hello world daemon that will just print hello world to standard
out every second. It will continue to do this until we stop it.

**Steps:**

.. code-block:: bash

    $ CONTAINER_ID=$(docker run -d base /bin/sh -c "while true; do echo hello world; sleep 1; done")

We are going to run a simple hello world daemon in a new container made from the busybox daemon.

- **"docker run -d "** run a command in a new container. We pass "-d" so it runs as a daemon.
- **"base"** is the image we want to run the command inside of.
- **"/bin/sh -c"** is the command we want to run in the container
- **"while true; do echo hello world; sleep 1; done"** is the mini script we want to run, that will just print hello world once a second until we stop it.
- **$CONTAINER_ID** the output of the run command will return a container id, we can use in future commands to see what is going on with this process.

.. code-block:: bash

    $ docker logs $CONTAINER_ID

Check the logs make sure it is working correctly.

- **"docker logs**" This will return the logs for a container
- **$CONTAINER_ID** The Id of the container we want the logs for.

.. code-block:: bash

    docker attach $CONTAINER_ID

Attach to the container to see the results in realtime.

- **"docker attach**" This will allow us to attach to a background process to see what is going on.
- **$CONTAINER_ID** The Id of the container we want to attach too.

.. code-block:: bash

    docker ps

Check the process list to make sure it is running.

- **"docker ps"** this shows all running process managed by docker

.. code-block:: bash

    $ docker stop $CONTAINER_ID

Stop the container, since we don't need it anymore.

- **"docker stop"** This stops a container
- **$CONTAINER_ID** The Id of the container we want to stop.

.. code-block:: bash

    docker ps

Make sure it is really stopped.


**Video:**

See the example in action

.. raw:: html

    <div style="margin-top:10px;">
      <iframe width="560" height="350" src="http://ascii.io/a/2562/raw" frameborder="0"></iframe>
    </div>

Continue to the :ref:`python_web_app` example.


Notes:
------

- **Docker daemon** The docker daemon is started by ``sudo docker -d``, Vagrant may have started
  the Docker daemon for you, but you will need to restart it this way if it was terminated. Otherwise
  it may give you ``Couldn't create Tag store: open /var/lib/docker/repositories: permission denied``