serge@UltraSoul-II:~$ VBoxManage sharedfolder add Louisa-VII -name «sharedfolder» -hostpath «/home/serge/Desktop»
VirtualBox Command Line Management Interface Version 1.5.6
(C) 2005-2008 innotek GmbH
All rights reserved.

[!] FAILED calling machine->CreateSharedFolder(Bstr(name), Bstr(hostpath), fWritable) at line 6236!
[!] Primary RC  = 0x80070057
[!] Full error info present: true , basic error info present: true 
[!] Result Code = 0x80070057
[!] Text        = Shared folder path '«/home/serge/Desktop»' is not absolute
[!] Component   = SharedFolder, Interface: ISharedFolder, {8b0c5f70-9139-4f97-a421-64d5e9c335d5}
[!] Callee      = IMachine, {31f7169f-14da-4c55-8cb6-a3665186e35e}
serge@UltraSoul-II:~$