# Get started with containers This guide assumes you have a working installation of Docker. To verify Docker is installed, use 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. Additionally, depending on your Docker system configuration, you may be required to preface each `docker` command with `sudo`. To avoid having to use `sudo` with the `docker` command, your system administrator can create a Unix group called `docker` and add users to it. For more information about installing Docker or `sudo` configuration, refer to the [installation](/installation) instructions for your operating system. ## Download a pre-built image # Download an ubuntu image $ docker pull ubuntu This will find the `ubuntu` image by name on [*Docker Hub*](/userguide/dockerrepos/#searching-for-images) and download it from [Docker Hub](https://hub.docker.com) to a local image cache. > **Note**: > When the image is successfully downloaded, you 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`. ## Running an interactive shell To run an interactive shell in the Ubuntu image: $ docker run -i -t ubuntu /bin/bash The `-i` flag starts an interactive container. The `-t` flag creates a pseudo-TTY that attaches `stdin` and `stdout`. To detach the `tty` without exiting the shell, use the escape sequence `Ctrl-p` + `Ctrl-q`. The container will continue to exist in a stopped state once exited. To list all containers, stopped and running use the `docker ps -a` command. ## 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][path] or unix://path For example: - `tcp://host:2375` -> TCP connection on host:2375 - `tcp://host:2375/path` -> TCP connection on host:2375 and prepend path to all requests - `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 /docker daemon -H 0.0.0.0:5555 & Download an `ubuntu` image: $ 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 /docker daemon -H tcp://127.0.0.1:2375 -H unix:///var/run/docker.sock & # Download an ubuntu image, use default Unix socket $ docker pull ubuntu # OR use the TCP port $ docker -H tcp://127.0.0.1:2375 pull ubuntu ## Starting a long-running worker process # Start a very useful long-running process $ JOB=$(docker run -d ubuntu /bin/sh -c "while true; do echo Hello world; sleep 1; done") # Collect the output of the job so far $ docker logs $JOB # Kill the job $ docker kill $JOB ## Listing containers $ docker ps # Lists only running containers $ docker ps -a # Lists all containers ## Controlling containers # Start a new container $ JOB=$(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=$(docker run -d -p 4444 ubuntu:12.10 /bin/nc -l 4444) # Which public port is NATed to my container? $ PORT=$(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: $(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, Docker only stores the diff (difference) between the source image and the current state of the container's image. To list images you already have, use the `docker images` command. # Commit your container to a new named image $ docker commit # List your images $ docker images You now have an image state from which you can create new instances. Read more about [*Share Images via Repositories*](/userguide/dockerrepos) or continue to the complete [*Command Line*](/reference/commandline/cli)