On my work, I have a box with WinXP, running Virtual Box as a host, and a Ubuntu Server 9.10 box as a guest. My problem is that the firewall on the corporate network does not allow Ubuntu to update the date and time against any NTP server (like pool.ntp.org or ntp.ubuntu.com). So, I need a way to keep the hour updated on the guest. Fortunately, VirtualBox has the ability to synchronize it from the host, the only thing I need to do was to install the Guest Additions package.
To do this, first, we need to click on Devices/Install Guest Additions (from the VirtualBox menu).
Then, on the Ubuntu Server, we install some pre-requisites:
$ aptitude install build-essential linux-headers-$(uname -r) -y
Now, we will mount the virtual CD-ROM (where the Guest Additions are):
$ mount /dev/cdrom /mnt/
And then, run the installer script (there is a 32-bit and 64-bit versions). For 32-bit (which is the most probable, as VirtualBox Open Source only supports 32-bit guests):
Or for 64-bit guest:
It should install the available modules (like timesync), and drop a fail message saying that X server
was not found, which is OK as we are working with a server without GUI.
Finally, we umount the CD-ROM:
$ umount /mnt/
Now, the guest box time should be sync with the host, so we have one less thing to worry about.