What characterizes a Docker image or container as active?

Question

One can use the command docker system df (mirror) (introduced in Docker 1.13.0) to see docker disk usage, e.g.:

username@server:~$ docker system df
TYPE                TOTAL               ACTIVE             SIZE                RECLAIMABLE
Images              44                  28                 114.7GB             84.84GB (73%)
Containers          86                  7                  62.43GB             41.67GB (66%)
Local Volumes       2                   1                  0B                  0B
Build Cache                                                0B                  0B

What does "active" mean? I.e., what characterizes an image or a container as active?

The Docker documentation on docker system df (mirror) doesn't explain it. The Docker glossary (mirror) doesn't contain the term "active".

I understand that:

"active" container means that the container is currently running (active containers can be listed with docker ps or equivalently docker container ls).

score 2 · Accepted Answer · answered Jun 04 '18 at 01:40

2

I believe it means:

Images: there is a container that exists using this image
Containers: container is currently running
Volumes: there is a container that exists with this volume mounted

answered Jun 04 '18 at 01:40

BMitch

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Thanks. If an image is active iff there is a container using it, then how is it possible that in my example (taken from real life) there are more active images (28) than active containers (7)? – Franck Dernoncourt Jun 04 '18 at 01:51
1

A container can exist that is not currently active. You should (and do) see fewer active images than you do total containers. – BMitch Jun 04 '18 at 02:06

What characterizes a Docker image or container as active?

1 Answers1