Prerequisites
OS Requirments
To install Docker Engine, you need the 64-bit version of one of these Ubuntu versions:
- Ubuntu Lunar 23.04
- Ubuntu Kinetic 22.10
- Ubuntu Jammy 22.04 (LTS)
- Ubuntu Focal 20.04 (LTS)
Docker Engine for Ubuntu is compatible with x86_64 (or amd64), armhf, arm64, s390x, and ppc64le (ppc64el) architectures.
Uninstall old versions
Before you can install Docker Engine, you must first make sure that any conflicting packages are uninstalled.
The unofficial packages to uninstall are:
- docker.io
- docker-compose
- docker-doc
- podman-docker
Run the following command to uninstall all conflicting packages:
for pkg in docker.io docker-doc docker-compose podman-docker containerd runc; do sudo apt-get remove $pkg; doneapt-get might report that you have none of these packages installed.
Installation methods
Install from a package
If you can’t use Docker’s apt repository to install Docker Engine, you can download the deb file for your release and install it manually. You need to download a new file each time you want to upgrade the Docker Engine.
1. Go to https://download.docker.com/linux/ubuntu/dists/
2. Select your Ubuntu version in the list.
3. Go to pool/stable/ and select the applicable architecture (amd64, armhf, arm64, or s390x).
4. Download the following deb files for the Docker Engine, CLI, containerd, and Docker Compose packages:
- containerd.io_<version>_<arch>.deb
- docker-ce_<version>_<arch>.deb
- docker-ce-cli_<version>_<arch>.deb
- docker-buildx-plugin_<version>_<arch>.deb
- docker-compose-plugin_<version>_<arch>.deb
5. Install the .deb packages. Update the paths in the following example to where you downloaded the Docker packages.
sudo dpkg -i ./containerd.io_<version>_<arch>.deb \
./docker-ce_<version>_<arch>.deb \
./docker-ce-cli_<version>_<arch>.deb \
./docker-buildx-plugin_<version>_<arch>.deb \
./docker-compose-plugin_<version>_<arch>.debThe Docker daemon starts automatically.
6. Verify that the Docker Engine installation is successful by running the hello-world image.
sudo service docker start
sudo docker run hello-worldThis command downloads a test image and runs it in a container. When the container runs, it prints a confirmation message and exits.
You have now successfully installed and started Docker Engine.
Uninstall Docker Engine
1. Uninstall the Docker Engine, CLI, container, and Docker Compose packages:
sudo apt-get purge docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin docker-ce-rootless-extras2. Images, containers, volumes, or custom configuration files on your host aren’t automatically removed. To delete all images, containers, and volumes:
sudo rm -rf /var/lib/docker
sudo rm -rf /var/lib/containerdYou have to delete any edited configuration files manually.
Run your image as a container
A container is a normal operating system process except that this process is isolated and has its own file system, its own networking, and its own isolated process tree separate from the host.
To run an image inside of a container, we use the docker run command. It requires one parameter and that is the image name. Let’s start our image and make sure it is running correctly. Execute the following command in your terminal.
docker run docker-gs-pingWhen you run this command, you’ll notice that you were not returned to the command prompt. This is because our application is a REST server and will run in a loop waiting for incoming requests without returning control back to the OS until we stop the container.
To stop the container, press ctrl-c. This will return you to the terminal prompt.
To publish a port for our container, we’ll use the --publish flag (-p for short) on the docker run command. The format of the --publish command is [host_port]:[container_port]. So if we wanted to expose port 8080 inside the container to port 3000 outside the container, we would pass 3000:8080 to the --publish flag.
Start the container and expose port 8080 to port 8080 on the host.
docker run --publish 8080:8080 docker-gs-pingRun in detached mode
This is great so far, but our sample application is a web server and we should not have to have our terminal connected to the container. Docker can run your container in detached mode, that is in the background. To do this, we can use the --detach or -d for short. Docker will start your container the same as before but this time will “detach” from the container and return you to the terminal prompt.
docker run -d -p 8080:8080 docker-gs-ping
d75e61fcad1e0c0eca69a3f767be6ba28a66625ce4dc42201a8a323e8313c14eDocker started our container in the background and printed the container ID on the terminal.
List containers
Since we ran our container in the background, how do we know if our container is running or what other containers are running on our machine? Well, to see a list of containers running on our machine, run docker ps. This is similar to how the ps command is used to see a list of processes on a Linux machine.
docker psCONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
d75e61fcad1e docker-gs-ping "/docker-gs-ping" 41 seconds ago Up 40 seconds 0.0.0.0:8080->8080/tcp inspiring_ishizakaThe ps command tells us a bunch of stuff about our running containers. We can see the container ID, the image running inside the container, the command that was used to start the container, when it was created, the status, ports that are exposed, and the names of the containers.
You are probably wondering where the name of our container is coming from. Since we didn’t provide a name for the container when we started it, Docker generated a random name. We’ll fix this in a minute but first, we need to stop the container. To stop the container, run the docker stop command, passing the container’s name or ID.
docker stop inspiring_ishizakaNow rerun the docker ps command to see a list of running containers.
docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMESStop, start, and name containers
Docker containers can be started, stopped, and restarted. When we stop a container, it is not removed but the status is changed to stopped and the process inside of the container is stopped. When we ran the docker ps command, the default output was to only show running containers. If we pass the --all or -a for short, we will see all containers on our system, that is stopped containers and running containers.
docker ps -allCONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
d75e61fcad1e docker-gs-ping "/docker-gs-ping" About a minute ago Exited (2) 23 seconds ago inspiring_ishizaka
f65dbbb9a548 docker-gs-ping "/docker-gs-ping" 3 minutes ago Exited (2) 2 minutes ago wizardly_joliot
aade1bf3d330 docker-gs-ping "/docker-gs-ping" 3 minutes ago Exited (2) 3 minutes ago magical_carson
52d5ce3c15f0 docker-gs-ping "/docker-gs-ping" 9 minutes ago Exited (2) 3 minutes ago gifted_mestorfIf you’ve been following along, you should see several containers listed. These are containers that we started and stopped but have not removed yet.
Let’s restart the container that we have just stopped. Locate the name of the container and replace the name of the container below in the restart command:
docker restart inspiring_ishizakaNow, list all the containers again using the ps command:
docker ps -aCONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
d75e61fcad1e docker-gs-ping "/docker-gs-ping" 2 minutes ago Up 5 seconds 0.0.0.0:8080->8080/tcp inspiring_ishizaka
f65dbbb9a548 docker-gs-ping "/docker-gs-ping" 4 minutes ago Exited (2) 2 minutes ago wizardly_joliot
aade1bf3d330 docker-gs-ping "/docker-gs-ping" 4 minutes ago Exited (2) 4 minutes ago magical_carson
52d5ce3c15f0 docker-gs-ping "/docker-gs-ping" 10 minutes ago Exited (2) 4 minutes ago gifted_mestorfNotice that the container we just restarted has been started in detached mode and has port 8080 exposed. Also, note that the status of the container is “Up X seconds”. When you restart a container, it will be started with the same flags or commands that it was originally started with.
Let’s stop and remove all of our containers and take a look at fixing the random naming issue.
Stop the container we just started. Find the name of your running container and replace the name in the command below with the name of the container on your system:
docker stop inspiring_ishizakaNow that all of our containers are stopped, let’s remove them. When a container is removed, it is no longer running nor is it in the stopped state. Instead, the process inside the container is terminated and the metadata for the container is removed.
To remove a container, run the docker rm command passing the container name. You can pass multiple container names to the command in one command.
Again, make sure you replace the container names in the below command with the container names from your system:
docker rm inspiring_ishizaka wizardly_joliot magical_carson gifted_mestorfRun the docker ps --all command again to verify that all containers are gone.
Now let’s address the pesky random name issue. Standard practice is to name your containers for the simple reason that it is easier to identify what is running in the container and what application or service it is associated with. Just like good naming conventions for variables in your code makes it simpler to read. So goes naming your containers.
To name a container, we must pass the --name flag to the run command:
docker run -d -p 8080:8080 --name rest-server docker-gs-pingdocker psCONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3bbc6a3102ea docker-gs-ping "/docker-gs-ping" 25 seconds ago Up 24 seconds 0.0.0.0:8080->8080/tcp rest-serverNow, we can easily identify our container based on the name.