Docker takes a conservative（保守的） approach（方法） to cleaning up unused objects（对象） (often referred to（被叫做） as “garbage collection”（垃圾回收）), such as images, containers, volumes, and networks: these objects are generally（通常） not removed unless you explicitly（明确） ask（要求） Docker to do so. This can cause Docker to use extra（额外） disk space. For each type of object, Docker provides a prune command. In addition（此外）, you can use docker system prune to clean up multiple types of objects at once. This topic shows how to use these prune commands.
Prune images
The docker image prune command allows you to clean up unused images. By default, docker image prune only cleans up dangling images. A dangling image is one that is not tagged and is not referenced（引用） by any container. To remove dangling images:
To remove all images which are not used by existing containers, use the -a flag:
$ docker image prune -a WARNING! This will remove all images without at least one container associated to them. Are you sure you want to continue? [y/N] y
By default, you are prompted（提示） to continue. To bypass（绕过） the prompt, use the -f or --force flag. 强制删除
You can limit which images are pruned（删除） using filtering（过滤） expressions（表达式） with the --filter flag. For example, to only consider images created more than 24 hours ago:
$ docker image prune -a --filter "until=24h"
Other filtering expressions are available. See the docker image prune reference for more examples.
Prune containers
When you stop a container, it is not automatically removed unless you started it with the --rm flag. To see all containers on the Docker host, including stopped containers, use docker ps -a. You may be surprised how many containers exist, especially on a development system! A stopped container’s writable layers still take up（占据） disk space. To clean this up, you can use the docker container prune command.
$ docker container prune WARNING! This will remove all stopped containers. Are you sure you want to continue? [y/N] y
By default, you are prompted to continue. To bypass the prompt, use the -f or --force flag.
By default, all stopped containers are removed. You can limit the scope using the --filter flag. For instance, the following command only removes stopped containers older than 24 hours:
$ docker container prune --filter "until=24h"
Other filtering expressions are available. See the docker container prune reference for more examples.
Prune volumes
Volumes can be used by one or more containers, and take up space on the Docker host. Volumes are never removed automatically, because to do so could（能） destroy（破坏） data.
$ docker volume prune WARNING! This will remove all volumes not used by at least one container. Are you sure you want to continue? [y/N] y
By default, all unused volumes are removed. You can limit the scope using the --filter flag. For instance, the following command only removes volumes which are not labelled with the keep label（下面的命令只删除未标记为保留标签的卷）:
$ docker volume prune --filter "label!=keep"
Other filtering expressions are available. See the docker volume prune reference for more examples.
Prune networks
Docker networks don’t take up much disk space, but they do create iptables rules, bridge network devices, and routing table entries. To clean these things up, you can use docker network prune to clean up networks which aren’t used by any containers（）.
$ docker network prune WArNING! This will remove all networks not used by at least one container. Are you sure you want to continue? [y/N] y
By default, you are prompted to continue. To bypass the prompt, use the -f or --force flag.
By default, all unused networks are removed. You can limit the scope using the --filter flag. For instance, the following command only removes networks older than 24 hours:
Prune everything
The docker system prune command is a shortcut that prunes images, containers, and networks. In Docker 17.06.0 and earlier, volumes are also pruned. In Docker 17.06.1 and higher, you must specify the --volumes flag for docker system prune to prune volumes.
$ docker system prune WARNING! This will remove: - all stopped containers - all networks not used by at least one container - all dangling images - all build cache Are you sure you want to continue? [y/N] y
If you are on Docker 17.06.1 or higher and want to also prune volumes, add the --volumes flag:
$ docker system prune --volumes WARNING! This will remove: - all stopped containers - all networks not used by at least one container - all volumes not used by at least one container - all dangling images - all build cache Are you sure you want to continue? [y/N] y
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