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save

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

Save one or more images to a tar archive (streamed to STDOUT by default)

Options:
      --help            Print usage
  -o, --output string   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