Mount volume to Docker image on OSX

Question

On a Mac, how do you mount a volume to a Docker container?

On my linux box, this is easy. All I need to do is something like -v /src/webapp:/opt/webapp when running the container. But Mac is different since I have to run boot2docker to run a VM in VirtualBox. I've tried running

boot2docker init
boot2docker up
boot2docker ssh # to poke around
boot2docker stop
VBoxManage sharedfolder add "boot2docker-vm" --name "Users" --hostpath /Users
boot2docker up
boot2docker ssh "sudo modprobe vboxsf"

but I get

modprobe: module vboxsf not found in modules.dep

If I ignore that and still try to mount on the VM like so

boot2docker ssh "sudo mkdir /test && sudo mount -t vboxsf Users /test"

I get

mount: mounting Users on /test failed: No such device

I feel like I'm missing something extremely simple, but I can't quite figure it out. Any help would be greatly appreciated.

Answer 1

Ok, after digging through a GitHub PR, I was able to figure out a way to do this. For the future readers out there, this process should be fixed in an upcoming release of boot2docker.

# assuming boot2docker and VirtualBox are installed
wget http://static.dockerfiles.io/boot2docker-v1.2.0-virtualbox-guest-additions-v4.3.14.iso
mv boot2docker-v1.2.0-virtualbox-guest-additions-v4.3.14.iso ~/.boot2docker/boot2docker.iso
# blow away your old boot2docker-vm if it exists (boot2docker down && boot2docker destroy)
boot2docker init
boot2docker up
# set DOCKER_HOST as instructed
boot2docker stop
VBoxManage sharedfolder add boot2docker-vm --name /Users --hostpath /Users
boot2docker up
# if you ssh into the VM now, you'll notice /Users is present, but empty; I don't know/care why.
boot2docker ssh "sudo mount -t vboxsf -o uid=1000,gid=50 /Users /Users"
# done

This worked for me so I hope it works for others. In the near future, I expect this issue to be solved by boot2docker, especially since the PR from which I got these commands was merged.

EDIT: boot2docker 1.3.0 supports this without any further changes. After updating, I ran these commands:

boot2docker destroy  # start over
boot2docker download # download the udpated ISO
boot2docker init
boot2docker up
# done

Answer 2

For folks finding this in the future who want to mount anything other than /Users, there's a script someone made as a gist on github that does the whole process for you and is awesome. Just use this. It saved me a lot of headache of having to keep screwing around with virtualbox. This is tested as of Docker 1.3.0 on my Mac running Yosemite.

EDIT:

Now that docker-machine cli has been deprecated in favor or docker-machine, here's how you can do it with docker-machine:

First, ssh into the docker-machine vm and create the folder we'll be mapping to:

docker-machine ssh $MACHINE_NAME "sudo mkdir -p \"$VOL_DIR\""

Now share the folder to VirtualBox:

WORKDIR=$(basename "$VOL_DIR")
vboxmanage sharedfolder add "$MACHINE_NAME" --name "$WORKDIR" --hostpath "$VOL_DIR" --transient

Finally, ssh into the docker-machine again and mount the folder we just shared:

docker-machine ssh $MACHINE_NAME "sudo mount -t vboxsf -o uid=\"$U\",gid=\"$G\" \"$WORKDIR\" \"$VOL_DIR\""

Note: for UID and GID you can basically use whatever integers as long as they're not already taken.

This is tested as of docker-machine 0.4.1 and docker 1.8.3 on OS X El Capitan.