These commands let you attach and retrieve string data to a virtual machine or to a VirtualBox configuration (by specifying global instead of a virtual machine name). You must specify a key (as a text string) to associate the data with, which you can later use to retrieve it. For example:

VBoxManage setextradata Fedora5 installdate 2006.01.01
VBoxManage setextradata SUSE10 installdate 2006.02.02

would associate the string "2006.01.01" with the key installdate for the virtual machine Fedora5, and "2006.02.02" on the machine SUSE10. You could retrieve the information as follows:

VBoxManage getextradata Fedora5 installdate

which would return

VirtualBox Command Line Management Interface Version 2.0.6
(C) 2005-2008 Sun Microsystems, Inc.
All rights reserved.

Value: 2006.01.01