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A simple Docker container and image garbage collection script.

  • Containers that exited more than an hour ago are removed.
  • Images that don't belong to any remaining container after that are removed.

Although docker normally prevents removal of images that are in use by
containers, we take extra care to not remove any image tags (e.g., ubuntu:14.04,
busybox, etc) that are in use by containers. A naive docker rmi $(docker images -q) will leave images stripped of all tags, forcing docker to re-pull the
repositories when starting new containers even though the images themselves are
still on disk.

This script is intended to be run as a cron job. You can also run it as a Docker
container (see below).


To use the script manually, run docker-gc.

Excluding Images From Garbage Collection

There can be images that are large that serve as a common base for
many application containers, and as such, make sense to pin to the
machine, as many derivative containers will use it. This can save
time in pulling those kinds of images. There may be other reasons to
exclude images from garbage collection. To do so, create
/etc/docker-gc-exclude, or if you want the file to be read from
elsewhere, set the EXCLUDE_FROM_GC environment variable to its
location. This file can contain image name patterns (in the grep
sense), one per line, such as spotify/cassandra:latest or it can
contain image ids (truncated to the length shown in docker images
which is 12.

An example excludes file might contain:


Running as a Docker Image

A Dockerfile is provided as an alternative to a local installation. By default
the container will start up, run a single garbage collection, and shut down.

Build the Docker Image

docker build -t coco/coco-docker-gc .

Running as a Docker Container

The docker-gc container requires access to the docker socket in order to
function, so you need to map it when running, e.g.:

docker run --rm -v /usr:/usr -v /var/run/docker.sock:/var/run/docker.sock coco/coco-docker-gc
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