moby--moby/docs/reference/commandline/save.md

save

Usage: docker save [OPTIONS] IMAGE [IMAGE...]

Save an image(s) to a tar archive (streamed to STDOUT by default)

  -o, --output=""    Write to a file, instead of STDOUT

Produces a tarred repository to the standard output stream. Contains all parent layers, and all tags + versions, or specified repo:tag, for each argument provided.

It is used to create a backup that can then be used with docker load

$ docker save busybox > busybox.tar
$ ls -sh busybox.tar
2.7M busybox.tar
$ docker save --output busybox.tar busybox
$ ls -sh busybox.tar
2.7M busybox.tar
$ docker save -o fedora-all.tar fedora
$ docker save -o fedora-latest.tar fedora:latest

It is even useful to cherry-pick particular tags of an image repository

$ docker save -o ubuntu.tar ubuntu:lucid ubuntu:saucy