HOWTO: start Ubuntu 10.04 on crypted raid via resuce disc to restore grub2

It's a known issue to everyone who ever set up an multi-boot environment using Windows and $other_OS, that Windows likes to replace the existing boot manger with its own.
Normally, you'd just boot up a rescue CD and reinstall your favorite boot loader (or that one that comes with your OS' rescue CD ).
Sadly, the Ubuntu 10.04 Alternate Desktop CD doesn't support my crypto-raid-setup. The rescue mode installer doesn't recognize my raid set up at all (even thou it gets assembled^^).
Therefore I've to repair it by hand:

After booting, the Ubuntu rescue CD offers to switch into a root terminal.

The raid was assembled automatically, so there is no need for doing it manually:

mdadm --assemble /dev/sda1 md0 

I am going to build a chroot environment in /mnt, change root into it and reinstall grub2:

At first I have to mount the crypto device for the root file system:

cryptsetup luksOpen /dev/md0 md0 
mount /dev/mapper/md0 /mnt 

Now we've to add the missing pseudo file systems:

mount -o bind /dev /mnt/dev
mount -t sysfs sys /mnt/sys
mount -t proc proc /mnt/proc

Last but not least: We must not forget to mount the boot device. In my case it is just an ordinary partition:

mount /dev/sda4 /mnt/boot

Our change root environment is ready for usage and we simply have to chroot into it:

chroot /mnt 

Now, grub2 can be easily restored:

grub-install /dev/sda

As a final step, we'll ensure that grub is up-to-date:

update-grub