Why could VirtualBox not find a registered machine named Windows_7?n

Question

I'm trying to change TCP/UDP of a virtual machine using VBoxManage setextradata.

Whenever I type the command:

sudo VBoxManage setextradata Windows_7 "VBoxInternal/Devices/pcnet/0/LUN#0/Config/guestEmule_TCP/Protocol" TCP

I get the following error:

VirtualBox Command Line Management Interface Version 2.1.4
(C) 2005-2009 Sun Microsystems, Inc.
All rights reserved.

[!] FAILED calling a->virtualBox->FindMachine(Bstr(a->argv[0]), machine.asOutParam()) at line 3688!
[!] Primary RC  = VBOX_E_OBJECT_NOT_FOUND (0x80BB0001) - Object corresponding to the supplied arguments does not exist
[!] Full error info present: true , basic error info present: true 
[!] Result Code = VBOX_E_OBJECT_NOT_FOUND (0x80BB0001) - Object corresponding to the supplied arguments does not exist
[!] Text        = Could not find a registered machine named 'Windows_7'
[!] Component   = VirtualBox, Interface: IVirtualBox, {339abca2-f47a-4302-87f5-7bc324e6bbde}
[!] Callee      = IVirtualBox, {339abca2-f47a-4302-87f5-7bc324e6bbde}

The virtual-machine has been created using GUI. Any idea?

$ cd /Users/marco/Library/VirtualBox/Machines/Windows_7
$ ls
Logs       Windows_7.xml
Windows 7.xml.1.5-macosx.bak
$ sudo vboxmanage registervm Windows_7.xml
VirtualBox Command Line Management Interface Version 2.1.4
(C) 2005-2009 Sun Microsystems, Inc.
All rights reserved.

[!] FAILED calling a->virtualBox->OpenMachine(Bstr(a->argv[0]), machine.asOutParam()) at line 762!
[!] Primary RC  = NS_ERROR_FAILURE (0x80004005) - Operation failed
[!] Full error info present: true , basic error info present: true 
[!] Result Code = NS_ERROR_FAILURE (0x80004005) - Operation failed
[!] Text        = Could not lock the settings file '/var/root/Library/VirtualBox/Windows_7.xml' (VERR_FILE_NOT_FOUND)
[!] Component   = Machine, Interface: IMachine, {ea6fb7ea-1993-4642-b113-f29eb39e0df0}
[!] Callee      = IVirtualBox, {339abca2-f47a-4302-87f5-7bc324e6bbde}

Answer 1

It fails because you are using sudo. VirtualBox is designed to be run by any user (in the vboxusers group), and sudo runs the command as the root user whose VirtualBox configuration is empty.

You can check that by typing:

sudo VBoxManage -nologo list vms # Should print only a newline
VBoxManage -nologo list vms # Detailled information about all your VMs