My Mac Mini (OS X Mountain Lion) always shuts down when starting it up after the recent upgrade. It displayed as below:
It always shuts down when it reaches 10~20% of the progress bar.
I tried to enter the safe mode by pressing Shift, but the result is the same.
Is there any way to avoid the auto upgrade and enter desktop directly?
Best Answer
This is probably a result of a corrupted filesystem -- the OS tries to repair it in order to start up, fails, and shuts down as a result. This in turn was probably caused by force-restarting the computer.
You can check this by starting in Recovery mode with Command-R, then running Disk Utility, selecting the startup volume in the sidebar (note that the volume will be listed under the disk it's on) -> First Aid tab -> Repair Disk button; this runs essentially the same repair process (and therefore will probably fail), but it'll tell you what it finds.
Assuming I'm right about the filesystem corruption, the next question is whether you need to recover any data from the disk. Is there anything on the computer you care about? Is it backed up? Are you sure it's backed up? If you need to get anything off the computer, do this before doing anything else! Getting data off an unbootable computer tends to be tricky, and depends greatly on what resources you have available (e.g. other Macs, external disks, etc).
Once you have everything you need copied off the computer, go back into Recovery mode, run Disk Utility, select the startup volume -> Erase tab -> set Format to "Mac OS Extended (Journaled)" -> Erase button. When that finishes, quit Disk Utility, select Reinstall Mac OS X, and follow the instructions. Note that this will download the installer files (about 4GB) over the internet, so it may take a while.
Relevant Apple KB articles: About OS X Recovery, Resolve startup issues and perform disk maintenance with Disk Utility and fsck, Erase and reinstall Mac OS X
EDIT: data recovery in a situation like this can be rather messy, with a number of things that need to be dealt with.
Finally, you need some way to actually copy the files: