Docker basics

Getting started with images

Use docker images to see what images you have locally on your host.

$ sudo docker images

Use docker search to see what images are available on Docker Hub.

$ sudo docker search fedora

Running a container

Use docker run to run an application inside a container. The following command pulls Fedora image, creates a container from it and runs Bash shell inside it.

$ sudo docker run -it fedora bash

Other useful options to use with run are for example -d to run a container in background (to daemonize it) or --name to give container a name which you can later use with docker stop/start.

See also Docker run reference.

Other useful commands regarding running containers are for example:

• docker ps to list running containers
• docker stop to stop running container and docker start to start stopped container
• docker logs to look inside container
• docker exec to enter running container, like: docker exec -it [container-id] bash

Creating an image

If you change anything (like install new packages in the above example with Bash) in the running container and exit the container the changes are not automatically saved into the Fedora image. If you want to save them in an image, use docker commit.

Another option how to create an image is by building it from Dockerfile, see below.

Writing a Dockerfile

There are already existing Dockerfiles in Fedora-Dockerfiles repository. You can use them as examples for creating your own Dockerfile. Each directory contains a Dockerfile and a README with instructions how to build the image and run a container from it.

A Dockerfile content can be as simple as:

FROM fedora:latest
CMD env

For description of instructions used in Dockerfile see Dockerfile reference and Best practices for writing Dockerfiles

Building an image from Dockerfile

In a directory with a Dockerfile run

$ sudo docker build -t "my-image" .

If the build is successful you can see the my-image image in docker images output.

See also Build your own image and Building an image from a Dockerfile for more thorough description.

Authors: Adam Samalik, Budh Ram Gurung, Jarek Prokop, Jiri Popelka, Nick Dirschel