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, but you can also run it as a Docker
container (see below).
Building the Debian Package
$ apt-get install git devscripts debhelper build-essential dh-make $ git clone https://github.com/spotify/docker-gc.git $ cd docker-gc $ debuild -us -uc -b
If you get lintian errors during
debuild --no-lintian -us -uc -b.
Installing the Debian Package
$ dpkg -i ../docker-gc_0.0.4_all.deb
This installs the
docker-gc script into
/usr/sbin. If you want it to
run as a cron job, you can configure it now by creating a root-owned
/etc/cron.hourly/docker-gc with the following contents:
To test that the job will actually run you can use this command
run-parts --test /etc/cron.hourly
To use the script manually, run
docker-gc. The system user under
docker-gc runs needs to have read and write access to
$STATE_DIR environment variable which defaults to
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
sense), one per line, such as
spotify/cassandra:latest or it can
contain image ids (truncated to the length shown in
which is 12.
An example image excludes file might contain:
spotify/cassandra:latest redis:.* 9681260c3ad5
Excluding Containers From Garbage Collection
There can also be containers (for example data only containers) which
you would like to exclude from garbage collection. To do so, create
/etc/docker-gc-exclude-containers, or if you want the file to be
read from elsewhere, set the
variable to its location. This file should container name patterns (in
grep sense), one per line, such as
An example container excludes file might contain:
Forcing deletion of images that have multiple tags
By default, docker will not remove an image if it is tagged in multiple
If you have a server running docker where this is the case, for example
in CI environments where dockers are being built, re-tagged, and pushed,
you can enable a force flag to override this default.
Forcing deletion of containers
By default, if an error is encountered when cleaning up a container, Docker
will report the error back and leave it on disk. This can sometimes lead to
containers accumulating. If you run into this issue, you can force the removal
of the container by setting the environment variable below:
Excluding Recently Exited Containers and Images From Garbage Collection
By default, docker-gc will not remove a container if it exited less than 3600 seconds (1 hour) ago. In some cases you might need to change this setting (e.g. you need exited containers to stick around for debugging for several days). Set the
GRACE_PERIOD_SECONDS variable to override this default.
This setting also prevents the removal of images that have been created less than
GRACE_PERIOD_SECONDS seconds ago.
By default, docker-gc will proceed with deletion of containers and images. To test your command-line options set the
DRY_RUN variable to override this default.
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.
The image is published as
Building the Docker Image
The image is currently built with Docker 1.6.2, but to build it against a newer
Docker version (to ensure that the API version of the command-line interface
matches with your Docker daemon), simply edit the
ENV DOCKER_VERSION line in
Dockerfile prior to the build step below.
Build the Docker image with
make -f Makefile.docker image or:
docker build -t spotify/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 /var/run/docker.sock:/var/run/docker.sock -v /etc:/etc:ro spotify/docker-gc
/etc directory is also mapped so that it can read any exclude files
that you've created.