The docker prune command can be used to periodically clean up infrequently used data

Scenario: After using the Docker engine for a long time, you will find that the disk space is getting larger and larger. Now you need to delete the unused data related to Docker to free up disk space.

First look at the docker system command

Docker system currently has four subcommands, namely:

docker system df
docker system events
docker system info
docker system prune

One of the most important commands of the docker system is the docker system prune command, which cleans up unused data, including image data and stopped containers.

See docker system help

[root@localhost ~]# docker system --help

Usage: docker system COMMAND

Manage Docker

Options:
      --help Print usage

Commands:
  df Show docker disk usage
  events Get real time events from the server
  info Display system-wide information
  prune Remove unused data

Run 'docker system COMMAND --help' for more information on a command.

docker system df

Provides an overview of overall Docker disk usage, including images, containers, and (local) volumes. So now we can check at any time how much resources Docker is using.

[root@localhost ~]# docker system df
TYPE TOTAL ACTIVE SIZE RECLAIMABLE
Images 10 6 2.652GB 1.953GB (73%)
Containers 6 6 6.922MB 0B (0%)
Local Volumes 0 0 0B 0B

docker system prune

If the previous command shows that docker has taken up too much space, we will start cleaning it up. There is a command that does it all:

[root@localhost ~]# docker system prune
WARNING! This will remove:
        - all stopped containers # Clean up stopped containers - all networks not used by at least one container # Clean up unused networks - all dangling images # Clean up abandoned images - all build cache # Clean up the build cache Are you sure you want to continue? [y/N] y
Total reclaimed space: 0B

According to the warning message, this command will delete all closed containers and dangling images. In the example, the image containing three 1GB random files has a name that is occupied:, which is a dangling image and will be deleted. At the same time, all intermediate images will be deleted.

Going a step further, use the -a option to do a deeper cleanup. At this time we will see more serious WARNING information:

$ docker system prune -a
WARNING! This will remove:
        - all stopped containers
        - all volumes not used by at least one container
        - All networks not used by at least one container
        - all images without at least one container associated to them
Are you sure you want to continue? [y/N] y
Deleted Images:
untagged: test:latest
deleted: sha256:c515ebfa2...
deleted: sha256:07302c011...
deleted: sha256:37c0c6474...
deleted: sha256:5cc2b6bc4...
deleted: sha256:b283b9c35...
deleted: sha256:8a8b9bd8b...
untagged: alpine:latest
untagged: alpine@sha256:58e1a1bb75db1...
deleted: sha256:4a415e366...
deleted: sha256:23b9c7b43...
Total reclaimed space: 2.151GB

This command will clean up the entire system and only keep the images, containers, volumes, and networks that are actually in use, so you need to be extra careful. For example, we cannot run the prune -a command in a production environment because some backup images (for backup, rollback, etc.) are sometimes needed. If these images are deleted, they need to be downloaded again when running the container.

At this point, all images that are not bound to containers will be deleted. Since the first prune command removes all containers, all images (which are not bound to any container) will be removed.

How to clean up None objects

Docker takes a conservative approach to cleaning up unused objects (often referred to as "garbage collection"), such as images, containers, volumes, and networks:
These objects are not normally deleted unless you explicitly ask Docker to do so. This may cause Docker to use additional disk space.
For each type of object, Docker provides a prune command.
Alternatively, you can use docker system prune to clean up multiple types of objects at once. This topic explains how to use these prune commands.

Trim Mirror

Clean up the none image (dangling image)
Command: docker image prune
By default, the docker image prune command only cleans up vanity images (images that are not tagged and not referenced by any other images).

root@instance-o70no2nw:~# docker image prune
WARNING! This will remove all dangling images.
Are you sure you want to continue? [y/N] y
Total reclaimed space: 0B

Clean up images that are not used by containers

Command: docker image prune -a

By default, you will be prompted to continue. To bypass the prompt, use the -f or --force flag.
You can use the --filter flag to limit which images are pruned using a filter expression. For example, to consider only images created 24 hours ago:

$ docker image prune -a --filter "until=24h"

Pruning container

Stopping a container will not automatically delete the container unless the --rm flag is specified when starting the container. Use the docker ps -a command to view all containers on the Docker host, including stopped containers. You might be surprised at how many containers there are, especially in development environments. The writable layer of a stopped container still takes up disk space. To clean these up, 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 will be prompted to continue. To bypass the prompt, use the -f or --force flag.

By default, all stopped containers are deleted. You can use the --filter flag to limit the scope. For example, the following command will only delete stopped containers that were created more than 24 hours ago:

Trimming rolls

Volumes can be used by one or more containers and take up space on the Docker host. Volumes are never automatically deleted because doing so would destroy 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

Pruning the network

Docker networks do not take up much disk space, but they do create iptables rules, bridge network devices, and routing table entries. To clean up these, you can use docker network prune to clean up networks that are not used by containers.

$ docker network prune

Trim Everything

The docker system prune command is a quick way to prune images, containers, and networks. In Docker 17.06.0 and earlier, pruning volumes is fine. In Docker 17.06.1 and later, you must explicitly specify the --volumes flag to the docker system prune command 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 using Docker 17.06.1 or higher, and you also want to prune volumes, use 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

Usually we can delete the scheduled task

For example, in my scenario, the image takes up a lot of disk space, so I schedule a task to delete images at 1 a.m. every day, deleting all images that have not been used for more than 72 hours:

[root@develop-server]# crontab -e
0 1 * * * docker image prune -a --force --filter "until=72h"

docker system info （docker info）

I believe everyone is familiar with the abbreviation of this command docker info

[root@localhost ~]# docker system info
Containers: 6
 Running: 6
 Paused: 0
 Stopped: 0
Images: 49
Server Version: 17.06.2-ce
Storage Driver: overlay
 Backing Filesystem: xfs
 Supports d_type: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins: 
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 6e23458c129b551d5c9871e5174f6b1b7f6d1170
runc version: 810190ceaa507aa2727d7ae6f4790c76ec150bd2
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 3.10.0-514.26.2.el7.x86_64
Operating System: CentOS Linux 7 (Core)
OSType: linux
Architecture: x86_64
CPUs: 24
Total Memory: 31.21 GiB
Name: localhost.localdomain
ID: YTL2:6RWX:IZK6:X4XC:XKMO:WVXD:LXPR:E5GN:GEJB:WIUX:L5YH:PDFB
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Experimental: false
Insecure Registries:
 127.0.0.0/8
Registry Mirrors:
 http://9zkjjecg.mirror.aliyuncs.com/
 https://docker.mirrors.ustc.edu.cn/
Live Restore Enabled: false

Detailed explanation

refer to:

docker-system - a new set of commands

Docker cleans up none image Prune command

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