Introduction
In the previous article we learned how to install Docker on ubuntu 18.04 and used some basic commands to manage docker service.In this session we will learn how to use Docker images from the official Docker hub and run as containers.
If you are not installed Docker on your system check out our previous tutorial http://bistux.com/bl/2020/07/18/how-to-install-and-use-docker-on-ubuntu-16-04-18-04-aws-ec2/
What is DockerHub?
DockerHub is a cloud-based repository run and managed by Docker Inc. It’s an online repository where Docker images can be published and used by users all over the world.
There are both public and private repositories. If you are a company, you can create e a private repository for use within your own organization, whereas public images can be used by anyone. You can also use official Docker images that are published publicly
Download images from Docker Hub
Docker containers are built from Docker images. By default, Docker pulls these images from Docker Hub. So most applications and Linux distributions you’ll need will have images published on Docker Hub.
You can search for images available on Docker Hub as :
docker search <imagename>
For example if you want ubuntu image type:
docker search ubuntu
This command will search for all available images matching the string name from Docker hub and list
In the OFFICIAL column, OK indicates that images are build and supported by the company.To know more about docker official images visit https://docs.docker.com/docker-hub/official_images/ .
After identifying the desired image you would like to use download it in your system locally using docker pull command
If you want to use ubuntu official image run :
docker pull ubuntu
You will get output as below
You can also search for official docker images on https://hub.docker.com/search?q=&type=image&image_filter=official
As you can see we can select tags for the image.If tag is not specified ,by default image with latest tag will be downloaded.
To see the images that have been downloaded to your computer, type:
docker images
The output should like
Running a Docker Container from Docker image
Now you can run the downloaded ubuntu latest image as container.To learn more about docker containers checkout https://www.docker.com/resources/what-container
we use combination of -i and -t switch to get the interactive shell access into the container.So our command will be
docker run -it ubuntu
After this your command prompt will switch and working inside the container.Output should look like :
docker@docker:~$ docker run -it ubuntu root@614cb7d3c611:/#
Note the container id in the command prompt. In this example, it is 614cb7d3c611. You’ll need that container ID later to identify the container when you want to remove it.
Now you can run any command inside the container as the original ubuntu machine. For example, let’s update the packages inside the container. You don’t need to prefix any command with
sudo, because you’re operating inside the container as the root user:
root@614cb7d3c611:/# apt update
Then Install an application.For example install nginx webserver on ubnutu container
root@614cb7d3c611:/# apt install nginx
This will install nginx from the official ubuntu repositories.Will check the nginx status after installation:
We can see nginx is running on the container.
Now we can exit from the container by using exit command
root@614cb7d3c611:/# exit exit
Next let us see how we can manage docker containers
How to Manage Docker Containers
After creating docker containers you will have active (running) and inactive containers in your system.
To view all active containers run :
docker ps
You will see output similar to the following:
CONTAINER ID IMAGE COMMAND CREATED In this tutorial we have started ubuntu docker container.Now it is not running but exist in our system
To view all containers (active & inactive ) run :
docker ps -a
We will get output look like
docker@docker:~$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 614cb7d3c611 ubuntu "/bin/bash" 2 hours ago Exited (0) About an hour ago confident_heisenberg
To start a stopped container run docker start command with container id or container name.Run command as
docker start 614cb7d3c611
The container will start, and you can use docker ps to see its status:
docker@docker:~$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 614cb7d3c611 ubuntu "/bin/bash" 2 hours ago Up 9 seconds confident_heisenberg
To stop a running container we use docker stop followed by container ID or container name .Here we use container name assigned by docker ie confident_heisenberg.So it will be as
docker stop confident_heisenberg
To remove a container run docker rm command followed by container id or name
docker rm 614cb7d3c611
Now we can run the same ubuntu image by giving a custom name using –name switch rather than default name assigned by Docker.
docker run --name=myubuntu -it ubuntu
Now check our container running with the given name
docker ps -a
Here we can our new container running with the given name “myubuntu”
Conclusion
In this tutorial we worked with docker images and containers.Also learned commands to manage docker containers with sample examples.