The example shows that the `--volumes` option is used, which in current
versions of docker only removes "anonymous" volumes, but preserves named
volume:
$ docker system prune -a --volumes
...
- all anonymous volumes not used by at least one container
...
But the example output showed that a named volume ("named-vol") was
deleted;
Deleted Volumes:
named-vol
Co-authored-by: Roberto Villarreal <rrjjvv@yahoo.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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