I was using Ubuntu Hardy Heron (8.04LTS) as a guest OS on VirtualBox. The system worked excellent, but it was about time to say goodbye and upgrade it to the latest Long Term Support version Lucid Lynx (10.04LTS).
I brought up a terminal, and run the command,
sudo update-manager --proposed
Now you see, I made a big mistake -- I had not backup-ed my data! Well, it is very easy to backup the whole Vbox image if there is enough space in the harddisk -- just make a copy of the vdi image file.
The upgrade went smoothly till it asked for a reboot. The system hung on the reboot. The icon of the virtual harddisk was not even flashing. I powered it off and restarted it. Hung again! I tried several times and even the Recovery mode. No luck! Then I realized I was going to lose several days work on it and started to panic... I told myself to calm down and leave the desk. After I came back with a cup of coffee, I knew what to do next.
VirtualBox lets us to mount an iso image as a CDROM and change the boot order so that we could boot from the CDROM. After that, we could mount the virtual harddisk and copy the data out. A lesson had been learned this day, so I made a whole image copy before I proceeded.
While I was copying the vdi image, a new thought hit me. The version of VirtualBox I used was very old, 2.2. Was it because that this aged VirtualBox could not support the latest version of Ubuntu?
So I decided to try the latest version (3.2.6) of VirtualBox first. Downloaded... Installed... Ran... It seemed that the system was hanging again during the restart. But this time, the icon of the virtual harddisk was flashing! Oh, it was just slow, too slow to me.
After a long wait, the system was up and running again! After the upgrade of VirtualBox, we need reinstall the Vbox Guest Addition. But that was trivial to me, being so delighted.