Probably the most convenient way to run Windows under Linux is to start with a dual-boot setup, then create (in Linux) a VMWare Server virtual machine based on the physical Windows partition. This ensures that you don’t have re-install Windows and your favorite applications.

But with great convenience comes great danger. When you power on the virtual machine, it will boot into GRUB (or LILO) which will ask which OS you want to run. No problem you’ll say, select Windows, it’s just a small inconvenience. Until the day your fingers err. Or, if GRUB has a timeout, the day you run to get a cup of water and come back to witness Linux booting. That means that the virtual machine and the host OS are now accessing the same partitions simultaneously.

The various VMWare tutorials strongly caution you to avoid this situations, which will likely result in data loss. But maybe you are wondering just how bad things can go (at least I always have). Well, about a month ago, facing a complete Linux re-install, I found the perfect opportunity to experiment. I had two Linux partitions (a JFS root and an EXT3 volume). So I powered up the virtual machine into Linux, and let it run its course, after which I rebooted.

The results? Surprisingly, the root JFS partition came out from fsck unscratched. That’s right, there were no errors, and nothing in /lost+found. The EXT3 partition, by contrast, was destroyed beyond repair (it started with a bad superblock, and went downhill from there as I tried to recover). Unphased, I decided to try again (after reformatting my EXT3 partition). The same thing happened. I have no ideea why, and I wouldn’t necessarily conclude that JFS is safer, but if you ever have the chance (or misfortune) to experiment, let me know how it goes…

And now, on to something more useful: how do you prevent such disasters? The answer is to force the VMWare partition to boot from a virtual floppy disk that makes the correct OS choice automatically (it could be GRUB with a single-item boot menu, or an NTLDR-based solution). Scott Bronson’s VMWare tutorial shows how to do this. Unfortunately, his method is rather inconvenient, requiring several reboots. So what follows is a simpler solution that replaces steps 3-10 from his Set up the Boot Disk section:

dd if=/dev/zero of=bootdisk.img bs=1k count=512
mke2fs -F bootdisk.img
mount -oloop bootdisk.img /mnt
mkdir -p /mnt/boot/grub
cp /boot/grub/stage[12] /mnt/boot/grub/
cat >/mnt/boot/grub/grub.conf <<EOF
timeout=3
title=Windows
root            (hd0,0)
chainloader     +1
makeactive
EOF
umount /mnt
grub --device-map=/dev/null <<EOF
device (fd0) bootdisk.img
root (fd0)
setup (fd0)
quit
EOF

The rest of Scott’s tutorial still applies — in particular, setting up different hardware profiles is important. How important? I’ll let you know next time I’m stuck with a complete Windows reinstall…