I have a MacBook Pro with Mac OSX installed and Ubuntu 12.04. I wanted to resize my Ubuntu partition, so I booted to a 10.04 liveCD and used GParted to "move/resize" my Ubuntu partition.
Unfortunately, I think GParted defaults to moving it 1000MiB to the right (i.e., adds 1000MiB of unallocated space to the left, and moves the partition right), something I didn't realize until after I had started the process.
In addition to doing this, I reduced its sized by ~10GiB (9.77GiB in the screenshot) from the right, and added an ext3 partition in that unallocated space (I'm trying to do Linux From Scratch)
How can I repair my system so that I can boot my Ubuntu 12.04 system? Perhaps it is something to do with Grub? I use the rEFIt Boot Manager, so everytime at boot, I have the option to load either OSX or Linux. I have already gone through the option to sync/update the MBR in rEFIt.
Here is a screenshot of GParted from my livecd booted up after the move:
Something very fortunate, though, is that in File Browser, in the left-hand panel, I can mount the "132 GB Filesystem", which is my 12.04 Filesystem which I moved and can no longer boot. I can browse it, and read files from it. Here is a screenshot:
It would appear that Grub is looking for Ubuntu in the wrong place. As the files are still there, nothing should be wiped. You will just need to fix Grub.
Fixing Grub with Boot Repair
The easiest way to do that is with "Boot Repair"
First boot into the live CD. Then install "Boot Repair" itself.
Enter these commands if you run Ubuntu 12.04
For Ubuntu 14.04
And for Ubuntu 14.10
This will also start the program after it has been installed.
Once the GUI opens up, click on the Recommended repair. This will reinstall the Grub2 boot-loader and find your Linux partition in its new location.
The guide uses steps from this source. Read it if you want more information.
Alternatively here is how to with the terminal only.