Originally Posted by thepenquin
...After searching, I've learned that repairing Grub2 is the problem. How-to (clarification) would be greatly appreciated. Thanks again for the great pages.
I know that this thread is stale, but I found it so others might and they deserve more information than is found here.
Each disk drive that can boot has a Master Boot Record (MBR). Each OS has their own code that gets written into this MBR. At power-on boot time, a small program in the hardware BIOS finds bootable disks, reads the slightly larger code from the MBR. The MBR code then finds the full OS on the disk drive. In addition to the MBR, boot details might also get written into the first few bytes each partition.
"GRUB Legacy" and now GRUB2 are one of the boot-time programs used by linux.
The end-user runs a linux program (update-grub or similar) that collects details from a linux install and writes the needed parts onto the MBR. These details include the path on disk where various OS parts are found. If there are multiple available OS configurations, there would likely be a menu to enable end-user choice of which OS to boot. Lastly, there is a small program needed to make all of this slightly smarter but still very small program.
GRUB problems typically take a couple of very specific forms:
- power on boot does not find useful things in the MBR
- GRUB starts and runs but does not work correctly
- GRUB starts and runs and works correctly but cannot find the parts it needs on the various OS partitions.
In the first case, you generally get messages from the hardware BIOS about a boot failure.
In the second case, you get GRUB errors about various internal details.
In the final case, GRUB complains about the various missing parts.
Each of these failures has its own corrective action. Typical trouble happen when something writes data over all or part of GRUB data. This is common when applying updates to one of the alternate-boot OS's.
The following might be a good start to recovery.