booting from usb stick

[iaw4]

latest virtualbox 4.3.20 (with extension pack), latest OSX 10.10.1. I would like to create a virtual machine whose only function it is to boot (linux guest) usb sticks. it won't need any vm hard drives. just the usb stick, sitting on /dev/disk2 .

after trial and error (I think the disk needed to be inserted and unmounted but not ejected, and I needed to be su), I succeeded with

# VBoxManage internalcommands createrawvmdk -filename ./rr2.vmdk -rawdisk /dev/disk2
RAW host disk access VMDK file ./rr2.vmdk created successfully.

I then changed the ownership of rr2.vmdk to the vbox user "me" and to make doublesure, I changed the permissions to be rw-rw-rw on rr2.vmdk. next, as the user, I created a virtualbox (via the gui) and started it once. this seemed to register the vm. good. finally, the coup de grace. I want to attach disk2. So I tried

$ VBoxManage storageattach "testusbstick" --storagectl "SATA" --port 0 --device 0 --type hdd --medium ./rr2.vmdk
VBoxManage: error: Permission problem accessing the file for the medium '/Users/me/./rr2.vmdk' (VERR_ACCESS_DENIED)
VBoxManage: error: Details: code VBOX_E_FILE_ERROR (0x80bb0004), component Medium, interface IMedium, callee nsISupports
VBoxManage: error: Context: "OpenMedium(Bstr(pszFilenameOrUuid).raw(), enmDevType, enmAccessMode, fForceNewUuidOnOpen, pMedium.asOutParam())" at line 178 of file VBoxManageDisk.cpp
VBoxManage: error: Invalid UUID or filename "./rr2.vmdk"

I tried variations on rr2.vmdk as the filename, but this was a no-go. What am I doing wrong here?

/iaw

[socratis]

From the manual, Chapter 8.18 VBoxManage storageattach:

--medium Specifies what is to be attached. The following values are supported:
...
• If a filename is specified, it must be the full path of an existing disk image (ISO, RAW, VDI, VMDK or other), which is then attached to the given device slot.