Comment 40 for bug 610898

I've been looking at how wubildr.mbr works - it finds and uses the first wubildr by scanning the root of all partitions, in BIOS order. On my computer the C: drive is the second partition and it never uses C:\WUBILDR. It always uses the one on my recovery partition /dev/sda1.

So Grub2 is using the existence of /host/wubildr to tell if it's a Wubi install, but I can delete it and it still boots fine - it's an 'artifact' as cjwatson would say. Therefore it shouldn't harm anything to have another 'artifact' on the /host partition when Wubi isn't installed on the Windows partition. If Grub2 considers this a Wubi indicator, there should either always be a /host/wubildr (or it shouldn't consider it important at all - i.e. the fact that root is loopmounted on /host/ubuntu/disks/root.disk should be enough).

Note that when Grub2 does find /host/wubildr - it updates it - to be compatible with the latest grub changes. The problem is, the one it updates often isn't the one used to boot. It really should be doing what WUBILDR.MBR does - check each partition in order and update the first one it finds (and/or update all it finds). This might also explain the booting problems we've been seeing lately when Wubi is installed to the same partition as Windows (bug 682337)