Original instructions with discussion can be found at the MIB (Mandriva International Backports) forum: How to reinstall Grub2 from a live ROSA Desktop Linux
Here are instructions on how to recover Grub2 (e.g., after Windows update/installation) using your live Rosa boot cd or usb (the latter is faster).
1. Boot from ROSA LiveCD or flash
2. Open a root console and type
You will see partitions of your disk:
Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x6e2792ad Device Boot Start End Blocks Id System /dev/sda1 * 273105 461740229 230733562+ 7 HPFS/NTFS/exFAT /dev/sda2 461744073 500103449 19179688+ 5 Extended /dev/sda5 461744128 500103449 19179661 83 Linux
3. In this case sda is the boot disk and sda5 is the root partition.
Now you have to mount your root partition:
mount /dev/sda5 /mnt
4. Now install Grub2 to MBR.
grub2-install --root-directory=/mnt/ /dev/sda
5. Finally, run update-grub2 to refresh Grub2 configuration:
6. ... and you're done.
You can now reboot and see again your grub boot loader