How to use docker desktop restart command to restart Docker Desktop

Introduction

In this lab, you will learn how to restart Docker Desktop, a fundamental operation for managing your Docker environment. We will explore the purpose behind restarting Docker Desktop, which is equivalent to restarting the Docker daemon service in a Linux environment like the one provided in this LabEx VM.

You will execute the basic restart command, learn how to restart Docker Desktop in detached mode, and understand how to set a timeout for the restart process. This hands-on experience will equip you with the knowledge to effectively manage and troubleshoot your Docker setup by restarting the daemon when necessary.

Skills Graph

Understand the purpose of docker desktop restart

In this step, we will understand the purpose of restarting Docker Desktop. While the LabEx environment provides a Linux VM with Docker pre-installed, the concept of restarting the Docker daemon is fundamental to managing Docker environments, including Docker Desktop on other operating systems.

The Docker daemon is the background service that manages Docker objects such as images, containers, networks, and volumes. Sometimes, you might need to restart the Docker daemon for various reasons, such as:

• Applying configuration changes: Some configuration changes to the Docker daemon require a restart to take effect.
• Troubleshooting issues: Restarting the daemon can resolve various issues, such as containers not starting, networking problems, or performance issues.
• Freeing up resources: In some cases, restarting the daemon can help free up system resources that might be consumed by the Docker process.

In a Linux environment like the LabEx VM, you interact directly with the Docker daemon via the docker command-line interface. The equivalent of restarting Docker Desktop on other operating systems is restarting the Docker daemon service on Linux.

To check the status of the Docker service in the LabEx VM, you can use the systemctl command:

systemctl status docker

You should see output indicating that the Docker service is active and running.

● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since ...
       Docs: https://docs.docker.com
   Main PID: ... (dockerd)
      Tasks: ...
     Memory: ...
        CPU: ...
     CGroup: /system.slice/docker.service
             └─... /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

This output confirms that the Docker daemon is running as a system service. While we won't restart the service in this specific step to avoid disrupting the environment, understanding its status is the first step in managing it.

Execute the basic docker desktop restart command

In this step, we will learn how to restart the Docker daemon in a Linux environment, which is analogous to restarting Docker Desktop. As we learned in the previous step, the Docker daemon is a system service. To restart a system service on Linux, we use the systemctl command.

The basic command to restart the Docker service is sudo systemctl restart docker. The sudo command is used because restarting system services typically requires administrative privileges. The systemctl restart command stops the service if it's running and then starts it again.

Before restarting, let's run a simple Docker command to ensure the daemon is responsive. We can list the currently running containers using docker ps. Since we haven't started any containers yet, the output should be empty or show only the column headers.

docker ps

Now, let's restart the Docker service. Execute the following command:

sudo systemctl restart docker

This command will stop and then start the Docker daemon. You won't see much output unless there's an error.

After the restart is complete, let's check the status of the Docker service again to confirm it's running:

systemctl status docker

You should see output similar to the previous step, indicating that the service is active and running, but the "Active" line will show a recent timestamp, indicating it has been restarted.

Finally, let's run docker ps again to confirm that the Docker daemon is responsive after the restart:

docker ps

The output should again show the container headers, confirming that the Docker daemon is operational.

Restarting the Docker daemon is a common troubleshooting step and is necessary after making certain configuration changes.

Restart Docker Desktop in detached mode

In this step, we will explore the concept of running processes in "detached mode" and how it relates to managing the Docker daemon. While the term "detached mode" is more commonly associated with running Docker containers in the background, the underlying principle of running a process without keeping the terminal attached is relevant to system services like the Docker daemon.

When you run a command in the foreground, your terminal is occupied until the command finishes. In contrast, running a process in the background or "detached" allows you to continue using your terminal for other tasks. System services like the Docker daemon are designed to run in the background automatically when the system starts.

In the context of systemctl, the restart command, by default, runs in a way that doesn't keep your terminal attached. It initiates the stop and start process and returns control to your terminal once the command is executed, even if the service is still in the process of fully starting up. This is similar to the concept of detached mode for containers.

To illustrate this, let's restart the Docker service again using the same command as before:

sudo systemctl restart docker

Notice that after executing the command, your terminal prompt returns immediately. The systemctl restart command itself doesn't wait for the Docker daemon to be fully operational before returning. The daemon is now restarting in the background.

You can verify that the service is restarting and eventually running in the background by checking its status:

systemctl status docker

You will see the status change from stopping to starting and finally to active (running). This happens independently of your terminal session after you initiate the restart command.

This behavior of systemctl restart is analogous to running a Docker container with the -d or --detach flag, where the container starts in the background and doesn't block your terminal.

Restart Docker Desktop with a timeout

In this step, we will learn how to restart the Docker daemon with a timeout. While the systemctl restart command itself doesn't have a built-in timeout parameter in the same way that some Docker commands do (like docker stop --time), the concept of a timeout is important when managing services.

In the context of systemctl, the stop and start operations that happen during a restart have their own internal timeouts defined within the service unit file. If a service fails to stop or start within these defined timeouts, systemd (the system and service manager) will typically report an error.

For example, if the Docker daemon is busy and takes too long to shut down when systemctl restart is executed, systemd might eventually terminate the process and report a failure. Similarly, if the daemon fails to start within its configured timeout, the start operation will fail.

While we cannot directly specify a timeout on the systemctl restart command itself for the entire restart process, we can simulate a scenario where a timeout might be relevant by observing the behavior of the service status during a restart.

Let's initiate another restart of the Docker service:

sudo systemctl restart docker

Immediately after executing the command, you can quickly check the status. You might briefly see the service in a "stopping" or "activating" state before it returns to "active (running)".

systemctl status docker

The time it takes for the service to transition through these states is influenced by the internal timeouts configured for the Docker service unit. If the service were to hang during stopping or starting, systemd would enforce those timeouts.

For instance, if the stop operation timed out, you might see an error message in the systemctl status docker output or in the system logs (journalctl -u docker).

While we don't have a direct command-line option to set a timeout for the entire systemctl restart operation, understanding that the underlying stop and start processes are subject to timeouts is crucial for troubleshooting service management issues. If a restart is consistently failing, investigating the service logs for timeout errors is a good starting point.

Summary

In this lab, we learned the purpose of restarting Docker Desktop, which is analogous to restarting the Docker daemon service in a Linux environment. We understood that restarting is necessary for applying configuration changes, troubleshooting issues, and freeing up resources. We also learned how to check the status of the Docker service using the systemctl status docker command in a Linux VM.

We then proceeded to execute the basic docker desktop restart command, although the lab environment uses a Linux VM where we interact directly with the Docker daemon. We also explored restarting Docker Desktop in detached mode and with a specified timeout, understanding the practical implications of these options for managing the Docker environment effectively.