Recently a friend made the same mistake I did when upgrading to Mavericks. So we both thought it was blog worthy. BEFORE YOU UPGRADE run Disk Utility to check for any hard drive errors. If you don’t and the upgrade process runs into hard disk errors it’s much more painful. In both our cases we couldn’t complete the install and we couldn’t roll back to the previous OS.
I am not a licensed Apple technician, and have no specialized training on Macintosh computers. You try any and all of the suggestions in this blog at your own risk. I have no way of knowing if these steps will work for you or cause further damage. The safest course of action is to take your computer to an Apple Store and have them repair it.
Time Machine to the Rescue
If you have time machine, restore from Time Machine and then Run Disk Utility. Of course once you do this you’ll want to consider replacing the hard drive prior to upgrading to Mavericks. If you don’t have any backups all is not lost.
Running Disk Utility
You can only run the repair mode of DU on drives you didn’t boot from. Prior to upgrading you should run in verify mode, and if you have no reported errors you should be good to go. If you get errors you need to boot in recovery mode and do a repair. The more modern Macs have a hidden recovery sector on the hard drive that allows you to boot in recovery mode. If you have Lion or later, even if the recovery partition is damaged it will attempt to boot from a recovery image on the Internet on Apple’s servers. You can also create a USB flash drive version of the recovery disk, and more details are available in this knowledgebase article.
Hold down Command-R while powering up to boot into recovery mode. On the damaged laptop we we’re working with, it wouldn’t even respond to the touchpad so we attached an external mouse. Once that was done it was easy enough to navigate to the Disk Utility app and run the repair. Unfortunately in this state. Disk Utility couldn’t repair the drive. It did report fixing some volume issues though. (As you’ll see later we probably should have just tried a normal restart at this point). If you can’t get into Recovery mode, you still have a few options. If you have a system DVD you can try to boot from that or you can try target disk mode (see below). If this works you can then run Disk Utility in repair mode on your damaged disk.
Target Disk Mode
Macs for a long time have supported something called Target Disk Mode over FireWire. This allows you to use the internal drive of one computer as an external drive on a second computer.
In the case of newer Macs TDM is supported over Thunderbolt. This does mean you likely have to shell out $40 or so for a Thunderbolt-to-Thunderbolt cable. That of course assumes you have two Mac’s with Thunderbolt. Just make sure you get a cable that is compatible with both Macs. You’ll probably also want to shell out $100 or so for a 1TB (or bigger) drive so you can start running Time Machine.
- Turn off both computers
- Connect the cable between the computers
- Boot the bad computer while you hold down the T key. In a minute or so your machine should turn on and the FireWire symbol should be displayed on it.
- Boot the second good computer.
- With luck the bad computer’s hard disk will show up on the good computer as an external disk or as a disk under the Networks area.
If the hard drive does appear, you can copy the files you want to save from one drive to another. When you have all your files copied you can use Disk Utility to erase and reformat the hard drive. Then you can install Mavericks on it but you might want to consider replacing the hard drive.
Target Disk Mode (reversed)
We couldn’t get the damaged drive to show up doing the above so we tried doing the process in reverse. The first two steps are the same then
- Boot the GOOD computer in target disk mode.
- Boot the bad computer normally. It should go into recovery mode.
- From recover mode set the startup disk to be the good computer. This will work best if the two computers are hardware compatible. We did it between two identical Mac PowerBooks.
- Restart the bad computer, it should now be running the OS from the good computer. With luck you should see the hard drive from the boot computer and the bad internal drive. Try to save the files from the internal drive to an external drive. Once you have your files you can also try running the Disk Utility in repair mode on the damaged drive.
A strange thing happened when we got to step 2 above, after trying all the other steps. The bad computer didn’t boot into recovery mode, instead it was offering to finish the Mavericks install or run disk utility. We ran DU to verify the disk and this time the disk passed! This seems very strange considering that from recovery mode DU reported it couldn’t repair the disk. Turns out I forgot Dogbert’s advice. The DU repair must have repaired enough to allow the new OS installation to proceed and the data files to be backed up.