Posts tagged windows

Time hackery in VirtualBox

:: hacking, virtualbox, virtualization, vm, windows

By: Maciej Barć

Unwanted (VDI) present

Recently I was given a task to run a outdated piece of commercial software on a very outdated (in)famous operating system. Unlucky for me on the given VDI (VirtualBox disk image) the so-called “Guests Additions” that enabled “better” time synchronization were already installed.

Fighting VBox time

So, this is what I had to do to keep the old clock:

  • turn off networking card in the virtual machine configuration, because we do not want the system to use NTP or other newt service to get the “new” time,
  • disable getting the host’s clock time: VBoxManage setextradata "WinXP" "VBoxInternal/Devices/VMMDev/0/Config/GetHostTimeDisabled" 1,
  • and… this magic: VBoxManage modifyvm "WinXP" --biossystemtimeoffset "-341597644449", this thing does the very weird thing of telling the virtual machine BIOS how much to set it back in time, the offset here is total milliseconds between some old date and current date.

Getting the old date

With the Python script snippet below you will get the milliseconds to set back the VirtualBox clock to 01.01.2012 01:00.

from datetime import datetime

round((datetime.strptime("01.01.2012 01:00", "%d.%m.%Y %H:%M")
      - * 1000)