Verifying Docker Engine and Container Status

As a developer or system administrator working with Docker, it’s essential to verify the status of the Docker engine and containers. This tutorial will guide you through the process of checking if the Docker engine is running and determining the status of a specific container.

Checking Docker Engine Status

To check if the Docker engine is running, you can use several methods:

1. Using docker info: Running docker info will display detailed information about the Docker installation, including the version, operating system, and other configuration details. If the Docker engine is not running, this command will exit with an error.
2. Using systemctl (for systemd-based systems): On Linux distributions that use systemd, you can check the status of the Docker service using systemctl. The command systemctl show --property ActiveState docker will display the current state of the Docker service.
3. Using systemctl is-active (for systemd-based systems): Alternatively, you can use systemctl is-active docker to check if the Docker service is active.

Here’s an example of how you can use these methods in a Bash script:

#!/usr/bin/env bash

# Check if Docker engine is running using docker info
if ! docker info > /dev/null 2>&1; then
    echo "Docker engine is not running. Please start it and try again!"
    exit 1
fi

# Alternatively, use systemctl (for systemd-based systems)
# if [ "$(systemctl is-active docker)" != "active" ]; then
#     echo "Docker engine is not running. Please start it and try again!"
#     exit 1
# fi

Checking Container Status

To check the status of a specific container, you can use the docker container inspect command with the -f option to specify the format of the output.

Here’s an example:

#!/usr/bin/env bash

CONTAINER_NAME="my_container"

# Check if the container is running using docker container inspect
if [ "$(docker container inspect -f '{{.State.Running}}' $CONTAINER_NAME)" = "true" ]; then
    echo "Container $CONTAINER_NAME is running."
else
    echo "Container $CONTAINER_NAME is not running."
fi

# Alternatively, check the Status field to avoid issues with containers in a crash loop
if [ "$(docker container inspect -f '{{.State.Status}}' $CONTAINER_NAME)" = "running" ]; then
    echo "Container $CONTAINER_NAME is running."
else
    echo "Container $CONTAINER_NAME is not running."
fi

Listing All Containers

If you want to list all containers, including their status, you can use the docker container ls command with the -a option:

docker container ls -a

This will display a table with information about each container, including its name, ID, image, command, and status.

Conclusion

In this tutorial, we covered various methods for checking the status of the Docker engine and containers. By using these techniques, you can ensure that your Docker environment is up and running as expected.