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Windows applications making GRUB 2 unbootable

Aug 29, 2010, 01:15 (0 Talkback[s])
(Other stories by Colin Watson)

"If you find that running Windows makes a GRUB 2-based system unbootable (Debian bug, Ubuntu bug), then I'd like to hear from you. This is a bug in which some proprietary Windows-based software overwrites particular sectors in the gap between the master boot record and the first partition, sometimes called the "embedding area". GRUB Legacy and GRUB 2 both normally use this part of the disk to store one of their key components: GRUB Legacy calls this component Stage 1.5, while GRUB 2 calls it the core image (comparison). However, Stage 1.5 is less useful than the core image (for example, the latter provides a rescue shell which can be used to recover from some problems), and is therefore rather smaller: somewhere around 10KB vs. 24KB for the common case of ext[234] on plain block devices. It seems that the Windows-based software writes to a sector which is after the end of Stage 1.5, but before the end of the core image. This is why the problem appears to be new with GRUB 2.

"At least some occurrences of this are with software which writes a signature to the embedding area which hangs around even after uninstallation (even with one of those tools that tracks everything the installation process did and reverses it, I gather), so that you cannot uninstall and reinstall the application to defeat a trial period. This seems like a fine example of an antifeature..."

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