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First steps with Docker

description

Common usage and commands

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_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 in the 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

# 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 -it 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 0.0.0.0:4243 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

# 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://127.0.0.1:4243 -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

# 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 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.

# 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 working_with_the_repository or continue to the complete cli