Docker error port is already allocated occurs when there is already a container is running on the same port on which we want to run a new process.

Here at Bobcares, we have seen several causes for this error while troubleshooting Docker issues as part of our Server Management Services for web hosts and online service providers.

Today we’ll take a look at the cause for this error and how to fix it.

Why does the docker error port is already allocated occur?

Before we get into the resolution part of the error, let us now see what causes this error to occur.

This error normally occurs when you try to run any container on a port that is already being used by some other container. This happens when we forget to kill the previously launched container.

For instance, the error appears as below.

This error means that there is already something running on port 4000. So it is not allowing any other container to run on the same port.

How we fix docker error port is already allocated

Recently, one of our customers approached us with this docker error which was showing the port to be already allocated. Let us now see how our Support Engineers resolve this error to our customers.

Initially, we find what container is running. For that, we ran the below command to know the currently running container’s ID:

$ docker container ls

Then we ran the below command to stop the already running container (Here, we replaced container_id with the actual container ID).

$ docker stop container_id

After that we asked the customer to resume the task that he wanted to do. Finally, it worked well.

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Conclusion

In short, this Docker error occurs when the previously running container is still active. Today, we saw how our Support Engineers resolve this error to our customers.