How to use docker container pause command to suspend containers

Introduction

In this lab, you will learn how to use the docker container pause command to suspend running containers. We will begin by creating and running a simple container using the hello-world image.

Following that, you will practice pausing the running container and verifying its paused state. Finally, you will learn how to unpause the container to resume its execution. This lab provides a hands-on introduction to managing container states using Docker commands.

Skills Graph

Create and run a simple container

In this step, we will learn how to create and run a simple Docker container. A container is a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another.

First, we need to pull the Docker image we will use. We will use the hello-world image, which is a very small image designed to demonstrate how Docker works.

docker pull hello-world

This command downloads the hello-world image from Docker Hub to your local machine. You should see output indicating the download progress and completion.

Now that we have the image, we can run a container based on it.

docker run hello-world

This command creates a new container from the hello-world image and runs it. When you run this container, it will print a message to your terminal explaining that your Docker installation is working correctly. After printing the message, the container will exit.

You should see output similar to this:

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
 1. The Docker client contacted the Docker daemon.
 2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
    (Assuming it was not already locally available)
 3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
 $ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:
 https://hub.docker.com/

For more examples and ideas, visit:
 https://docs.docker.com/get-started/

This output confirms that you have successfully pulled and run your first Docker container.

Pause the running container

In the previous step, we ran a simple container that exited immediately. To demonstrate pausing and unpausing, we need a container that stays running. We will use a simple ubuntu container and keep it running in the background.

First, let's pull the ubuntu image.

docker pull ubuntu

This command downloads the ubuntu image from Docker Hub.

Now, we will run an ubuntu container in detached mode (-d) so it runs in the background. We will also use the tail -f /dev/null command to keep the container running indefinitely.

docker run -d ubuntu tail -f /dev/null

This command will output the container ID. Copy this ID, as we will need it to pause the container.

<container_id>

Now that we have a running container, we can pause it using the docker pause command followed by the container ID.

docker pause <container_id>

Replace <container_id> with the actual ID of your running Ubuntu container.

This command will pause all processes within the specified container. The container will still exist, but its processes will be suspended.

Verify the container is paused

In the previous step, we paused a running container. Now, let's verify that the container is indeed in a paused state.

We can use the docker ps command to list running containers and check their status.

docker ps

This command will show you a list of currently running containers. If your Ubuntu container is paused, it will still appear in this list, but its status will indicate that it is paused. Look for the container ID you paused in the previous step.

The output should show your container with a status like Up ... (Paused).

Alternatively, you can use the docker container inspect command to get detailed information about a specific container, including its state. Replace <container_id> with the actual ID of your paused Ubuntu container.

docker container inspect <container_id>

This command will output a large JSON object containing all the configuration and state information for the container. You need to look for the "State" field within this output.

To specifically check if the container is paused using docker container inspect, you can filter the output using tools like grep.

docker container inspect <container_id> | grep Paused

If the container is paused, this command will output a line similar to "Paused": true,. This confirms that the container's state is indeed paused.

Unpause the container

In the previous step, we verified that our Ubuntu container was paused. Now, let's unpause it and resume its execution.

We use the docker unpause command followed by the container ID to unpause a container. Replace <container_id> with the actual ID of your paused Ubuntu container.

docker unpause <container_id>

This command will resume all processes within the specified container that were suspended when it was paused.

After unpausing the container, you can verify its status again using the docker ps command.

docker ps

This time, the output for your Ubuntu container should show a status like Up ... without the (Paused) indicator. This confirms that the container is now running normally again.

Finally, to clean up, you can stop and remove the container. First, stop the container:

docker stop <container_id>

Then, remove the container:

docker rm <container_id>

These commands will stop the running container and then remove it from your system.

Summary

In this lab, we learned how to use the docker container pause command to suspend containers. We started by creating and running a simple container using the hello-world image, which demonstrated the basic process of pulling an image and running a container.

Following the creation and execution of a container, we explored how to pause a running container using the docker container pause command and verified its paused state. Finally, we learned how to resume the container's execution using the docker container unpause command.