I updated my Macbook to OS X Lion over the weekend and had a nasty scare. I could not boot back to Ubuntu, nor could I see my Ubuntu partition. That is the moment where you think, "Is everything baked up? What will I loose?". I remember that I switched from Evolution to Thunderbird last month; my email was lost. The truth is that everything was okay, and if this happens to you, you can fix this in a few minutes like I did.
I do not know what the OS X installer did. Maybe it resized the
partitions. rEFIt did not report an issue. It verified that the the
partition tables were synced. Grub did not know about Ubuntu though. I
saw the grub prompt (
grub>) instead of a message about the selected
partition. I followed ubuntu mactel instructions to install Ubuntu, so I
know Ubuntu should be on located on hd0,3. I typed:
grub> root (hd0,3)
grub> find /boot/grub/stage1
Find will report if it finds the boot information. If it does not find
stage1, then you can try an alternate disk and partition, such as
root (hd1,1) or
root (hd0,4). When you find stage1 you can configure
grub to fix boot:
grub setup (hd0,3)
I restarted and Ubuntu booted correctly. No data was lost.
The reason that OS X could not see my Ubuntu partition was because MacFuse was compiled for 32bit. Lion is 64bit. I installed the 64bit version of MacFuse to see Ubuntu and my data.