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Frequently Asked Questions for Docker

Q1. How do I confirm that Docker is running?#

Open a Command Line (CMD) and type:

docker version

You can also type this in the Command Line:

docker run hello-world


Q2. What does it mean that Docker daemon is not running?#

The message: “Docker: error during connect: Post… This error may also indicate that docker daemon it not running” means that Docker is not running in your system.
You will first have to execute Docker. Please go to Step 1 on How to Install Docker. Install-Docker-FAQ-Q2
After you successfully install and Docker is running, you will get the following message: Install-Docker-FAQ-Q2b

Q3. I have a Virtual Box installed on my system. Since I installed Docker, I cannot execute any of my virtual machines anymore. Why?#

Be aware that enabling Docker in your system will prevent you to keep using Virtual Box.
When Hyper-V technology is enabled, it interferes with Virtual Box.
More information about this in

Q4. Is my Virtual Box lost?#

No. Your Virtual Box is not lost. You just cannot execute a virtual machine once you have Docker on.

Q5. How do I check how much disk resources Docker is using?#

Go to the Command Line (CMD) and type:

 docker system df


Q6. How can I check if the SDK container is running correctly?#

Go to the Command Line (CMD) and type:

docker ps


Q7. What should I do with a “License file not found” error?#

Make sure you have replaced the TOKEN with your key in the run command. Refer to Manual Installation Steps

Q8. What is a “connection refused” error when I am trying to upload images with curl?#

You are probably receiving this message because the container is not running.
To verify that type docker ps in the Command Line (CMD) in the terminal to see the status of containers.
It should look like this (1 container running in port 8080): Install-Docker-FAQ-Q6
If the status doesn’t show any containers at all, then the SDK container is not actually running in your system.
You will need to first run it. Refer to Manual Installation Steps.

Q9. What does “you have a container running with this license” mean?#

This means that you currently have a container running with this license–perhaps on another machine.
If you need to install the SDK in another machine, please uninstall this one first. Refer to Uninstall Steps to uninstall the SDK..
Or, go to add another license for this machine. Install-Docker-FAQ-Q9b

Q10. How do I change the port of the container?#

If you are already using port 8080, then you can change the port of the container including the -p option like in the command below:

docker run -t -v license:/license -e TOKEN=MY_TOKEN -p 8085:8080 platerecognizer/alpr

The -p 8085:8080 part will bind the port 8085 of your host machine with the port 8080 inside the container.

Q11. How do I resolve this error message: ERROR:root:Local system time may be out of sync.#

Make sure that the time and date of your Docker host is set correctly. On Windows, Check this tip for some solutions to fix the issue.

Q12. Why does Docker on Windows on a Dual CPU setup only utilize half the logical cores?#

It appears that there is an issue with Docker on windows not being able to take advantage of both NUMA nodes properly.
Recommendation: switching the OS to a Linux distro should resolve the issue.

Q13. What are some good Docker monitoring tools?#

To monitor Docker, you can use Prometheus, an open source software. You can see a comparison of different monitoring tools for Docker. Docker also provides these built in commands:

  1. docker ps - List running containers
  2. docker stats - Display a live stream of container(s) resource usage statistics
  3. docker inspect - Return low-level information on Docker objects