can I mount a file from volume in docker to the container?

Question

I put one security file like id_rsa in the docker volume larrycai_vol, trying to mount this into the container as a file.

$ docker volume inspect larrycai-vol
[
    {
        "CreatedAt": "2018-05-18T06:02:24Z",
        "Driver": "local",
        "Labels": {},
        "Mountpoint": "/var/lib/docker/volumes/larrycai-vol/_data",
        "Name": "larrycai-vol",
        "Options": {},
        "Scope": "local"
    }
]

Do we have some command like below (it doesn't work now)

docker run -it -v larrycai-vol/id_rsa:/root/.ssh/id_rsa own_ubuntu

I know it works if I mount file from docker host

docker run -it -v $PWD/.ssh/id_rsa:/root/.ssh/id_rsa own_ubuntu

IMO this should work for files as well https://stackoverflow.com/questions/23137544/how-to-map-volume-paths-using-dockers-volumes-from — Oleg Sklyar, May 18 '18 at 06:18

score 6 · Accepted Answer · answered May 18 '18 at 08:43

Please, let me a couple of considerations furthermore the proposed solution to avoid further misunderstandings.

Docker allows mounting volumes (deployed from path dir of your host to docker path, i.e, -v $PWD/.ssh:/root/.ssh = it'd replace complete .ssh folder in destination, so, it's not recommended although possible)
Docker allows mounting named volumes (deployed from named volume name to docker path, i.e, -v larrycai-vol:/root/.ssh = it'd replace complete .ssh folder in destination, so, it's not recommended although possible)
Docker allows mounting files from host to a docker (example: -v $PWD/.ssh/id_rsa:/root/.ssh/id_rsa = your second example)
Docker allows mounting files from named volume to a docker (example: -v /var/lib/docker/volumes/YOUR_NAMED_VOLUME_NAME/_data/file:/dest_dir/file = what you're trying to do)

Your mistake is that you're telling docker to mount id_rsa from your larrycai-vol directory, not from docker named volume. In other words, three following commands are equivalent:

docker run -it -v ./larrycai-vol/id_rsa:/root/.ssh/id_rsa own_ubuntu
docker run -it -v $PWD/larrycai-vol/id_rsa:/root/.ssh/id_rsa own_ubuntu
docker run -it -v larrycai-vol/id_rsa:/root/.ssh/id_rsa own_ubuntu

So, if larrycai-vol directory (not named volume, but directory in your host) doesn't exist, command doesn't work as you want.

Definitively, to do what you're trying you have to create a bind volumeto the directory where named volume store data.

docker run -it -v /var/lib/docker/volumes/larrycai-vol/_data/id_rsa:/root/.ssh/id_rsa own_ubuntu

solution 4 shall work, but looks ugly ;-), hope we can support extra file paramter in mount tag this `--mount source=|` — Larry Cai, May 18 '18 at 12:59
It hasn't already been provided by docker. I also hope in following versions it can be possible. — Alejandro Galera, May 18 '18 at 13:01
mounting a file from a named volume (4th bullet point) is certainly something that one should NOT do. — Xaser, May 12 '19 at 17:18

can I mount a file from volume in docker to the container?

1 Answers1