[all variants] Does upgrading to the next release write to the MBR?

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http://ubuntuforums.org – I have Ubuntu 11.10 and Debian. Debian is what I use every day, and is what the GRUB 2 installation on the Master Boot Record points to. If I upgrade Ubuntu to 12.04, will it overwrite the MBR with it's own GRUB? In other words, will it run grub-install without asking me? If it does, it should find Debian, so I can still boot into Debian and run grub-install to get things back the way they were. But there's several opportunities for things to go wrong there, and anything with the potential to cause GRUB problems makes me nervous. Maybe I'm being paranoid (I tend to do that sometimes), bu (Hardware)