1. Overview
In a previous article, we learned how to remove a Docker image. However, a Docker image can only be removed if no Docker container is using that image. Hence, to remove a Docker image, it is necessary to remove all the Docker containers running with that image.
In this tutorial, we'll learn to remove Docker containers using different approaches.
2. Why Remove a Docker Container?
When a Docker container completes its execution, it attains the exited state. Such containers do not consume any CPU or memory, but they still use the machine's disk space. Also, stopped containers are not automatically removed unless we use the –rm flag while running the Docker container.
Hence, as more and more containers are moved into the exited state, the overall disk space consumed by them increases. As a result, we might not be able to launch new containers, or the Docker daemon would stop responding.
To avoid such scenarios, it is recommended to either run the Docker containers using the –rm flag or periodically remove the Docker containers manually.
Let's now learn how to remove Docker containers.
3. Remove a Single Docker Container
First, we'll start a CentOS Docker container in non-interactive mode. By doing so, the container will stop immediately after we run the container:
$ docker run --name mycontainer centos:7
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
418c28b4b04e centos:7 "/bin/bash" 6 seconds ago Exited (0) 5 seconds ago mycontainer
Now let's remove the Docker container, mycontainer, using the docker rm command:
$ docker rm mycontainer
mycontainer
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
We can also use Docker container id instead of the Docker container name to remove the Docker container using the docker rm command:
$ docker rm 418c28b4b04e
4. Remove Multiple Docker Containers
We can also remove multiple Docker containers using the docker rm command. The docker rm command accepts a space-separated list of the Docker container name or id and removes all of them:
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
23c70ec6e724 centos:7 "/bin/bash" 6 seconds ago Exited (0) 5 seconds ago mycontainer3
fd0886458666 centos:7 "/bin/bash" 10 seconds ago Exited (0) 9 seconds ago mycontainer2
c223ec695e2d centos:7 "/bin/bash" 14 seconds ago Exited (0) 12 seconds ago mycontainer1
$ docker rm c223ec695e2d mycontainer2 23c70ec6e724
c223ec695e2d
mycontainer2
23c70ec6e724
In the example above, there were three Docker containers in the exited state which we removed using the docker rm command.
We can use the Docker container name and id interchangeably with any Docker command. Notice that we used the Docker container id for the mycontainer1 and mycontainer3 and the container name for mycontainer2.
5. Remove All the Docker Containers
Consider a scenario where too many stopped Docker containers are present on the machine, and now we wish to remove them all. Of course, we can use the above approach and pass all the containers id to the docker rm command. But let's look into a more optimized and simple command to remove all the Docker containers:
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b5c45fa5764f centos:7 "/bin/bash" 4 seconds ago Exited (0) 3 seconds ago mycontainer1
ed806b1743cd centos:7 "/bin/bash" 9 seconds ago Exited (0) 7 seconds ago mycontainer2
2e00a052eb12 centos:7 "/bin/bash" 13 seconds ago Exited (0) 12 seconds ago mycontainer3
$ docker rm $(docker ps -qa)
b5c45fa5764f
ed806b1743cd
2e00a052eb12
The command docker ps -qa return the numeric ids of all the containers present on the machine. All these ids are then passed to the docker rm command, which will iteratively remove the Docker containers.
We can also use the docker container prune command to remove all the stopped containers:
$ docker container prune -f
Here, we use the -f flag to avoid the prompt for confirmation.
6. Forcefully Remove a Running Docker Container
All the commands that we discussed in the examples above works only if the Docker container is stopped. If we try to remove a running container without stopping it first, we'll get an error message similar to this:
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
f84692b27b0a centos:7 "/bin/bash" 59 seconds ago Up 58 seconds mycontainer
$ docker rm mycontainer
Error response from daemon:
You cannot remove a running container f84692b27b0a18266f34b35c90dad655faa10bb0d9c85d73b22079dde506b8b5.
Stop the container before attempting removal or force remove
One way to remove a running Docker container is first to stop that container using the docker stop command and then use the docker rm command to remove it.
Another way is to forcefully remove such containers using the -f option:
$ docker rm -f mycontainer
mycontainer
We can use the -f option to remove a single Docker container, multiple Docker containers, or all the Docker containers.
7. Conclusion
In this tutorial, we gained an understanding of why it is necessary to remove Docker containers. First, we learned to remove a container from a Linux machine. Further, we bulk removed the Docker containers using the docker rm and docker prune command.
Finally, we looked at how to remove Docker containers forcefully, which are in the running state.
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