Docker Cookbook

1.19 Sharing Data Between Containers | 33

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the host. Docker created it under 
/var/lib/docker/volumes/
. From the host you can
read and write to it. Changes will persist and be available if you restart the container:
$ sudo touch /var/lib/docker/volumes/dbba7caf8d07b862b61b39.../foobar2
$ docker start b5835d2b951e
$ docker exec -ti b5835d2b951e /bin/bash
root@b5835d2b951e:/# ls /cookbook
foobar foobar2
To share this data volume with other containers, use the 
--volumes-from
option. Let’s
start fresh and create a data container, and then start another container that will
mount the volume from this source data container:
$ docker run -v /data --name data ubuntu:14.04
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
$ docker inspect -f {{.Mounts}} data
[{4ee1d9e3d453e843819c6ff... /var/lib/docker/volumes/4ee1d9e3d453e843819c6ff... \
/_data /data local true]
The data container is not running. Still, the volume mapping exists
and the volume has persisted in 
/var/lib/docker/vfs/dir
. You can
remove the container and the volume only with 
docker rm -v
data
. If you do not use the 
rm -v
option to delete containers and
their volumes, you will end up with lots of orphaned volumes.
Even though the data container is not running, you can mount the volume from it
with the 
--volumes-from
option:
$ docker run -ti --volumes-from data ubuntu:14.04 /bin/bash
root@b94a006377c1:/# touch /data/foobar
root@b94a006377c1:/# exit
exit
$ sudo ls /var/lib/docker/volumes/4ee1d9e3d453e843819c6ff...
foobar
See Also
•
Understanding
volumes
• Data 
container
• Docker 
volumes
• Official Docker 
documentation
• The aha moment of 
Docker volumes