Tuesday, 11 February 2014

Restore a deleted Mac partition table

Last Friday, I was attempting to install Windows on my partners iMac without a DVD/CD drive, and I had set up the drive in bootcamp, and committed the system to reboot. The Windows setup started, however when selecting the installation directory, Windows did not like the formatting that Bootcamp had setup, so it offered to delete the partition and recreate it's own NTFS partition - which I opted to do.

Still, Windows setup didn't like something about the disk - spitting out and error and not being able to proceed. A bit of (in hindsight amateurish) Google'ing and I found a solution to "clean the disk" which I accidentally interpreted as cleaning the partition. This was my downfall. What made the situation worse is that the TimeMachine backup which I thought was complete was in fact not complete, and hadn't been backing up for some time.

Crisis!

Having had a little experience with data recovery in the past, I straight away jumped on the data recovery search train and started my search for software which I could use to rebuild the partition table. The problem I found was that many sites and software packages were offering solutions based on disks which were either external drives or secondary to the operating system, which were useless to me, as the entire boot drive's partition table had been deleted.

Many hours of searching and looking at possible solutions included a number of data recovery programs which promised to recover partition tables or extract files from the hard disk but none prevailed. All I could do is boot from a USB stick or use the inbuilt Internet Recovery feature which comes with all Macs. This was dangerous as I didn't want to write to the hard disk, and I wanted maximise my recovery chances by avoiding any writing at all.

The hardest part was finding software which could look at HFS+ data recovery, or rebuilding partitions. Many programs promised the world, but even the trial versions did not deliver. In the end I found a completely free solution which I am happy to share with you now, so you can enjoy my happiness at being able to recover all that data by rebuilding the partition table.

In order to follow my guide, this only applies to Macs which don't have an optical drive.

You'll need:
  • Another computer to download install and use some software to help with this recovery.
  • A USB stick/thumb drive of at least 1gb in size (I used a 4gb stick)
  • A copy of an Ubuntu iso file (I used ubuntu-13.10-desktop-amd64+mac.iso - note the amd64+mac component of this file)
  • Download a copy of the freeware software "unetbootin"
  • A (relatively) fast internet connection with an ethernet connect to your modem - wifi won't work.
  • A USB keyboard and mouse - any should do. The bluetooth wireless mouse and keyboard that comes with most macs won't work throughout the whole process.
The guide:
  1. Once you've downloaded Ubuntu and unetbootin, insert your USB stick and burn a copy of Ubuntu to the USB stick so that you can boot from the USB stick (you can browse to the .iso file you downloaded which I would recommend instead of downloading on the fly).
  2. Plug the USB stick, keyboard and mouse into the damaged Mac and hold the option key when powering up. If you're using a non-mac keyboard, hold ALT on the left.
  3. Choose the USB icon to boot from and the unetbootin menu should appear, follow the menu to boot into Ubuntu which is the live version of ubuntu which you can use to test the OS, rather than install it.
  4. Within a few minutes you should be in the ubuntu desktop environment. Once there, go into the settings (cog icon on the left menu bar)
  5. Open software settings and enable all software from all repositories.
  6. Open a terminal window (click the ubuntu menu, then type terminal) and type "sudo apt-get update". This will update your software repositories which is necessary for the next step.
  7. Install a software program called TestDisk by typing: "sudo apt-get install testdisk". This will download and install testdisk on your system which we will use to interpret the damaged hard drive.
  8. Once complete, type sudo testdisk to open the program.
  9. The next few parts will be a bunch of questions asked by the software before it can begin scanning.
    • Decide if you want a log created (I didn't care)
    • Select the disk which relates to your Mac's Drive
    • Then it asks about the partition type - select Mac
    • The next choice should be analyse
    • And then quick search.
    • It will start scanning with items in green lines indicating partitions the software has found.
  10. After it has finished you should get some results showing the missing partitions!!
  11. At this screen, do not touch the keyboard yet. Grab the mouse and select the results and copy them. Then either write them down (not recommended as you could make a mistake which could cause SERIOUS problems later) or email them to yourself.
  12. My results looked like this: 
  13. You can now reboot your Mac.
  14. Once it restarts take out the Ubuntu USB stick and hold down command (or the windows key if a non-mac keyboard) and R
  15. This will start Internet recovery. Once at the Internet recovery menu, you can open a terminal window using the utilities menu.
  16. With the terminal window type ls (to LiSt the files of the directory you're in)
  17. Type "cd .." to navigate up one level in the folder structure.
  18. Type ls again
  19. Continue to do this until you reach the root directory, which will show "dev" when you do a ls command. Then type cd /dev/
  20. This will move you to the dev directory. At this point ensure your terminal window is as big as possible, use full screen if you can. Type ls again
  21. This will list all the devices on the mac. This is also where it becomes a bit difficult, so it's important to focus on what you are doing otherwise you could damage your disk even more.
  22. Type pdisk - this opens the pdisk program within terminal which allows you to make changes to your computers hard disk.
  23. Type L (note the capital) and hit enter - this will list the disks attached to your computer and should indicate which disk is required - this will be the disk we are looking for. For me, it was rdisk0 or rdisk1 (I can't remember which).
  24. Quit the program, by typing q, and then reopen the program by typing "pdisk /dev/rdisk0" (CAREFUL: your rdisk number could be different based on your result in step 23)
  25. Type c (lowercase). It should tell you that no partition map exists - which is correct - it doesn't yet, but we are about to recreate it.
  26. Type i (also lowercase). It will tell you some stuff about block sizes and the size of your hard disk in blocks.
  27. Type c again. Before anything else - get your info from step 12 above.
  28. In my example the first block was 409640 and the length was the "size in sectors" part, which for me was 1756533456. So type your first block part, hit enter then type your length. Then hit enter again and name it anything just don't use spaces - I just typed the word: one 
  29. Repeat this process for as many partitions that you had - I had 2. So I then typed c again to tell the program I had another partition to create, then 1756943096 and 1269536 and named it: two
  30. Then once you've typed in all your partitions, instead of typing c again, type w
  31. It might prompt you to confirm you want to write the changes, say that you do (y)
  32. Then type q to quit the program. Now restart your mac, holding down the option key.
  33. Your hard drive should appear. And you can boot back into OSX.
  34. First thing you should do now is setup a Time Machine Backup
I hope this has saved you from a sticky situation like it did for me. If you want to share the incredible moment I had yelling like Boris did in James Bond's Goldeneye feel free to buy me a drink:


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2 comments:

  1. There is a reason why I bought a Mac, it was not to be one of the cool kids that wanted the best of the best. No it was because of the music production I do on it. Hours and hours sitting in front of my Mac copying, pasting, moving, deleting, hour after hour just beating on my Mac in a endless assault to get my work done. That is the key part, my work. I work from home, it is great, but even if it is from home it is still work and it still needs to get done. So my Mac, I have it because it is fast, gets the job done and comes back for more.

    But what happens when it doesn't want to do those things anymore?

    I move around massive amounts of information and yes even on the almighty Mac this can cause a problem after a while. Things fragment, programs get corrupted issues come up. My light speed Mac slows down to a crawl and all of the sudden I simply can not get any work done. Because I work from home there is no IT guy to call and ask to come fix it. No instead I have to figure out what is wrong. I am lucky, I did, but not after trying everything under the sun first and wasting countless hours looking for one program that can do what I needed instead of ten programs. One program to lead them all….okay that was a lame Lord of the rings reference, but that program was/is Detox My Mac. A simple to use program that did not just fix my issues, it put my Mac on overdrive again. A few clicks and my Mac was clean and ready to rock and roll again.

    Read more here:- http://detox-my-mac.com?duhhf9265hskfhf98346

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