Imagine that you want to share a host folder named c:\Buildbox\src into the guest box on /external/src. In this case you should do something like this:
On the Windows box
boot2docker save
cd "C:\Program Files\Oracle\VirtualBox"
vboxmanage sharedfolder add boot2docker-vm --name extsrc --hostpath c:\BuildBox
VBoxManage setextradata boot2docker-vm VBoxInternal2/SharedFoldersEnableSymlinksCreate/extsrc 1
boot2docker start
boot2docker ssh
On the boot2docker vm
$ sudo mkdir /external
$ sudo mkdir /external/src
$ sudo chown -R docker:docker /external
$ sudo vi /var/lib/boot2docker/profile
#! /bin/sh
mount -t vboxsf extsrc /external/src
$ sudo chmod 770 /var/lib/boot2docker/profile
$ sudo chown docker:docker /var/lib/boot2docker/profile
Exit the box and run
boot2docker save
boot2docker start
boot2docker ssh
$ mount
And you should be able to see a line like :
none on /external/src type vboxsf (rw,nodev,relatime)
Additionally ... you may need symbolic links (i.e. npm install) ... to activate that you will need:
If your user is of the Administrator type (rather than a Standard account), there's no way to run VB with symlinks working without the UAC prompt cos you have to start the VBox as Administrator (cmd with elevated privileges)
Make sure your user has proper access to the shared folder on host system. As mentioned here earlier, execute VBoxManage setextradata VM_NAME VBoxInternal2/SharedFoldersEnableSymlinksCreate/SHARE_NAME 1 in a console from the C:\Program Files\VirtualBox folder. Don't forget to substitute VM_NAME with the name of your VM and SHARE_NAME with the name of the shared folder (as it appears in the VM settings).