Docker: create a persistent volume in a specific directory

Question

I need to create a persistent volume for Docker. The volume must be named extra-addons and located in /mnt/.

I run this command:

sudo docker volume create /mnt/extra-addons

I got this error message:

Error response from daemon: create /mnt/extra-addons: "/mnt/extra-addons" includes invalid characters for a local volume name, only "[a-zA-Z0-9][a-zA-Z0-9_.-]" are allowed. If you intended to pass a host directory, use absolute path

Note that when I simply run: sudo docker volume create extra-addons, I do not face this problem but when I inspect the volume in question using sudo docker inspect extra-addons, I see it is located in a place I do not want:

[
    {
        "CreatedAt": "2018-04-21T14:40:25+03:00",
        "Driver": "local",
        "Labels": {},
        "Mountpoint": "/var/lib/docker/volumes/extra-addons/_data",
        "Name": "extra-addons",
        "Options": {},
        "Scope": "local"
    }
]

I mean I rather want to see the volume like this: /mnt/extra-addons

Any idea?

Answer 1

I found the solution:

I had to install local-persist plugin.

I had to mount the volume to create to the mount point as follows:

 sudo docker volume create -d local-persist -o mountpoint=/mnt/ --name=extra-addons

Check if I got what I expected:

sudo docker volume inspect extra-addons

Result:

[
    {
        "CreatedAt": "0001-01-01T00:00:00Z",
        "Driver": "local-persist",
        "Labels": {},
        "Mountpoint": "/mnt/",
        "Name": "extra-addons",
        "Options": {
            "mountpoint": "/mnt/"
        },
        "Scope": "local"
    }
]

That was what I am looking for.

Answer 2

If you don't want to install any plugins to your docker, I would recommend to create a symbolic link for your volume:

$ docker volume create <myVolume>
$ docker volume inspect <myVolume> 
[
    {
        "CreatedAt": "0001-01-01T00:00:00Z",
        "Driver": "local",
        "Labels": {},
        "Mountpoint": "/var/lib/docker/volumes/<myVolume>/_data",
        "Name": "<myVolume>",
        "Options": {},
        "Scope": "local"
    }
]
$ mkdir /mnt/<myVolume>
# if you already have data in your volume, you should copy it to `/mnt/<myVolume>` now
$ sudo rm -rf /var/lib/docker/volumes/<myVolume>/_data
$ sudo ln -s /mnt/<myVolume> /var/lib/docker/volumes/<myVolume>/_data

Now feel free to use your volume as usual (with all your data beeing in /mnt as you wanted)

Answer 3

I don't think using the local-persist driver is the way to go. It hasn't been updated in a while. You can mount a local (host) directory into a docker container using docker mount.

Running the following creates a new container with a mounted directory mapped to my desktop.

mkdir extra-addons
docker run -it -v /Users/me/Desktop/extra-addons:/mnt/extra-addons busybox /bin/sh
ls

You can now see a mnt folder in root of your container.

bin dev etc home mnt proc root sys tmp usr var

Creating a new file in the container

touch /mnt/extra-addons/test.txt

Creates a test.txt file on my host machine. At the specified path. This is now a two way read/write shared folder. Multiple containers can mount the same folder. And it'll persist once you shut your container/s down.