:title: Learn Basic Commands
:description: Common usage and commands
:keywords: Examples, Usage, basic commands, docker, documentation, examples
Learn Basic Commands
====================
Starting Docker
---------------
If you have used one of the quick install paths, Docker may have been
installed with upstart, Ubuntu's system for starting processes at boot
time. You should be able to run ``sudo docker help`` and get output.
If you get ``docker: command not found`` or something like
``/var/lib/docker/repositories: permission denied`` you will need to
specify the path to it and manually start it.
.. code-block:: bash
# Run docker in daemon mode
sudo <path to>/docker -d &
Download a pre-built image
--------------------------
.. code-block:: bash
# Download an ubuntu image
sudo docker pull ubuntu
This will find the ``ubuntu`` image by name in the :ref:`Central Index
<searching_central_index>` and download it from the top-level Central
Repository to a local image cache.
.. NOTE:: When the image has successfully downloaded, you will see a
12 character hash ``539c0211cd76: Download complete`` which is the
short form of the image ID. These short image IDs are the first 12
characters of the full image ID - which can be found using ``docker
inspect`` or ``docker images -notrunc=true``
Running an interactive shell
----------------------------
.. code-block:: bash
# Run an interactive shell in the ubuntu image,
# allocate a tty, attach stdin and stdout
# To detach the tty without exiting the shell,
# use the escape sequence Ctrl-p + Ctrl-q
sudo docker run -i -t ubuntu /bin/bash
.. _dockergroup:
The sudo command and the docker Group
-------------------------------------
The ``docker`` daemon always runs as the root user, and since Docker version
0.5.2, the ``docker`` daemon binds to a Unix socket instead of a TCP port. By
default that Unix socket is owned by the user *root*, and so, by default, you
can access it with ``sudo``.
Starting in version 0.5.3, if you (or your Docker installer) create a
Unix group called *docker* and add users to it, then the ``docker``
daemon will make the ownership of the Unix socket read/writable by the
*docker* group when the daemon starts. The ``docker`` daemon must
always run as the root user, but if you run the ``docker`` client as a user in
the *docker* group then you don't need to add ``sudo`` to all the
client commands.
.. warning:: The *docker* group is root-equivalent.
**Example:**
.. code-block:: bash
# Add the docker group if it doesn't already exist.
sudo groupadd docker
# Add the connected user "${USERNAME}" to the docker group.
# Change the user name to match your preferred user.
# You may have to logout and log back in again for
# this to take effect.
sudo gpasswd -a ${USERNAME} docker
# Restart the docker daemon.
sudo service docker restart
.. _bind_docker:
Bind Docker to another host/port or a Unix socket
-------------------------------------------------
.. warning:: Changing the default ``docker`` daemon binding to a TCP
port or Unix *docker* user group will increase your security risks
by allowing non-root users to potentially gain *root* access on the
host (`e.g. #1369
<https://github.com/dotcloud/docker/issues/1369>`_). Make sure you
control access to ``docker``.
With ``-H`` it is possible to make the Docker daemon to listen on a
specific IP and port. By default, it will listen on
``unix:///var/run/docker.sock`` to allow only local connections by the
*root* user. You *could* set it to ``0.0.0.0:4243`` or a specific host IP to
give access to everybody, but that is **not recommended** because then
it is trivial for someone to gain root access to the host where the
daemon is running.
Similarly, the Docker client can use ``-H`` to connect to a custom port.
``-H`` accepts host and port assignment in the following format:
``tcp://[host][:port]`` or ``unix://path``
For example:
* ``tcp://host:4243`` -> tcp connection on host:4243
* ``unix://path/to/socket`` -> unix socket located at ``path/to/socket``
``-H``, when empty, will default to the same value as when no ``-H`` was passed in.
``-H`` also accepts short form for TCP bindings:
``host[:port]`` or ``:port``
.. code-block:: bash
# Run docker in daemon mode
sudo <path to>/docker -H 0.0.0.0:5555 -d &
# Download an ubuntu image
sudo docker -H :5555 pull ubuntu
You can use multiple ``-H``, for example, if you want to listen on
both TCP and a Unix socket
.. code-block:: bash
# Run docker in daemon mode
sudo <path to>/docker -H tcp://127.0.0.1:4243 -H unix:///var/run/docker.sock -d &
# Download an ubuntu image, use default Unix socket
sudo docker pull ubuntu
# OR use the TCP port
sudo docker -H tcp://127.0.0.1:4243 pull ubuntu
Starting a long-running worker process
--------------------------------------
.. code-block:: bash
# Start a very useful long-running process
JOB=$(sudo docker run -d ubuntu /bin/sh -c "while true; do echo Hello world; sleep 1; done")
# Collect the output of the job so far
sudo docker logs $JOB
# Kill the job
sudo docker kill $JOB
Listing all running containers
------------------------------
.. code-block:: bash
sudo docker ps
Bind a service on a TCP port
------------------------------
.. code-block:: bash
# Bind port 4444 of this container, and tell netcat to listen on it
JOB=$(sudo docker run -d -p 4444 ubuntu:12.10 /bin/nc -l 4444)
# Which public port is NATed to my container?
PORT=$(sudo docker port $JOB 4444 | awk -F: '{ print $2 }')
# Connect to the public port
echo hello world | nc 127.0.0.1 $PORT
# Verify that the network connection worked
echo "Daemon received: $(sudo docker logs $JOB)"
Committing (saving) a container state
-------------------------------------
Save your containers state to a container image, so the state can be re-used.
When you commit your container only the differences between the image the
container was created from and the current state of the container will be
stored (as a diff). See which images you already have using the ``docker
images`` command.
.. code-block:: bash
# Commit your container to a new named image
sudo docker commit <container_id> <some_name>
# List your containers
sudo docker images
You now have a image state from which you can create new instances.
Read more about :ref:`working_with_the_repository` or continue to the
complete :ref:`cli`