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page_title: First steps with Docker
page_description: Common usage and commands
page_keywords: Examples, Usage, basic commands, docker, documentation, examples
# First steps with Docker
## Check your Docker install
This guide assumes you have a working installation of Docker. To check
your Docker install, run the following command:
# Check that you have a working install
$ docker info
If you get `docker: command not found` or something like
`/var/lib/docker/repositories: permission denied` you may have an
incomplete Docker installation or insufficient privileges to access
Docker on your machine.
Please refer to [*Installation*](/installation/#installation-list)
for installation instructions.
## Download a pre-built image
# Download an ubuntu image
$ sudo docker pull ubuntu
This will find the `ubuntu` image by name on
[*Docker Hub*](/userguide/dockerrepos/#find-public-images-on-docker-hub)
and download it from [Docker Hub](https://hub.docker.com) 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 --no-trunc=true`
**If you're using OS X** then you shouldn't use `sudo`.
## Running an interactive shell
# 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
# note: This will continue to exist in a stopped state once exited (see "docker ps -a")
$ sudo docker run -i -t ubuntu /bin/bash
## 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 gain *root* access on the host. Make sure
> you control access to `docker`. If you are binding
> to a TCP port, anyone with access to that port has full Docker access;
> so it is not advisable on an open network.
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 `0.0.0.0:2375` 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:2375` -> TCP connection on
host:2375
- `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
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
# Run docker in daemon mode
$ sudo <path to>/docker -H tcp://127.0.0.1:2375 -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://127.0.0.1:2375 pull ubuntu
## Starting a long-running worker process
# 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 containers
$ sudo docker ps # Lists only running containers
$ sudo docker ps -a # Lists all containers
## Controlling containers
# Start a new container
$ JOB=$(sudo docker run -d ubuntu /bin/sh -c "while true; do echo Hello world; sleep 1; done")
# Stop the container
$ docker stop $JOB
# Start the container
$ docker start $JOB
# Restart the container
$ docker restart $JOB
# SIGKILL a container
$ docker kill $JOB
# Remove a container
$ docker stop $JOB # Container must be stopped to remove it
$ docker rm $JOB
## Bind a service on a TCP port
# 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 an 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.
# Commit your container to a new named image
$ sudo docker commit <container_id> <some_name>
# List your containers
$ sudo docker images
You now have an image state from which you can create new instances.
Read more about [*Share Images via
Repositories*](/userguide/dockerrepos/#working-with-the-repository) or
continue to the complete [*Command
Line*](/reference/commandline/cli/#cli)
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