Please help this n00b get his Mac OSX back!

January 9, 2009 4:50 PM

Help me get my OSX back! Ubuntu/Mac questions inside.

Ok, so I did one of those very stupid things that is probably fairly easily fixable but is still a major pain in the butt, especially to someone who knows nothing about Mac OS.

I was playing around with the Ubuntu LiveCD and wanted to try the USB drive installation. Instead of choosing "Create a USB startup disk" option, I started an "Install", thinking that it would give me that option.

I stopped before any damage was done, but when I tried to boot back into my Mac OS there was no boot disk present. I suspect that the Ubuntu install, even though I aborted it, still repartitioned my Mac HD.

So I booted back into the Ubuntu, and started up GParted. I wanted to check with the experts here before I did anything colossally stupid.

I see:

/dev/sda1  |   fat32   | EFI | 200.00MiB | ... | boot/dev/sda2  |   hfs+    |     |  74.21GiB | ... |unallocated|unallocated|     | 125.53MiB | ... |

I'm guessing sda2 is my MacHD, and that I need to set the flag to 'boot'. But I don't recognize the other partitions, and when I untag the 'boot' flag from sda1, it turns into 'msftres', something I also don't recognize.

I am running Ubuntu 8.10, and my Mac OSX was 10.4 (if I remember correctly--it's the OS just before the newest one).

Can someone please help me get my Mac OSX back? While I'm not a complete tech n00b, where partitions and other OSs are concerned I feel rather helpless.

posted by war wrath of wraith to computers & internet (8 comments total)

Do you have your install disk around?

Boot into it and run through the setup screens. When you get to the point where you select a volume, move your mouse to the top of the screen. A menu bar should appear. Under some menu there's a way to launch "Terminal". Do that and run this command:

bless --folder /Volumes/[your HD name]/System/Library/CoreServices --file /Volumes/[your HD name]/System/Library/CoreServices/boot.efi --setBoot

Then type "reboot" and hopefully everything works!

BTW: the first partition is for EFI, which is the next generation version of BIOS. Specs require a 200MB partition to store stuff on, such as filesystem drivers. The second partition is your OS X partition.
posted by sbutler at 5:15 PM on January 9

I once had something similar happen when I was mucking around with Boot Camp. Tried reinstalling Windows, hit the wrong partition, freaked out, rebooted to nothingness.

The solution - and I don't recommend this unless you run out of all other options, which is probably the only time you would try this - was to attempt to wipe the disk in Disk Utility while booted off an install disk. A friend explained:

That is probably exactly what happened - Windows can only write to the MBR partition table on the drive, and GPT partitions store two copies of the partition table, one at the beginning of the drive and one at the end. Wikipedia “GUID Partition Table” for more info.

Why the Mac lost track of the GPT partition table is anybody’s guess, but I wonder if the partitioning tool in Disk Utility noticed that the GPT table was overwritten and restored the secondary table.

Not sure if Ubuntu acts similarly, but you never know.
posted by Remy at 7:49 PM on January 9

I would boot the 10.4 install disk, start Disk Utility, either shrink or expand the second partition, and hope Disk Utility corrects any problems with the GPT/MBR.
posted by PueExMachina at 11:46 AM on January 10

Thanks for your suggestions. The problem seems to be bigger than I originally thought -- I found out that none of the 'alternative' startup methods work. In other words, holding down a key (c, x, alt, what have you) during startup does nothing. Consequently, I have been unable to boot from the original installation disc. As a matter of fact, the only thing that seems to work is the Ubuntu LiveCD which starts up automatically. (Holding down the mouse button while starting up does still eject the disc.)

What gives??? Have I done some permanent damage to the BIOS? How? And, more importantly, how can I get my Mac back?

Any help would really be appreciated.
posted by war wrath of wraith at 3:54 PM on January 10

There is no way Ubuntu messed with your EFI (you don't have a BIOS). Are you sure you're holding down the option key at the right time? You have to start holding it after the computer turns on, but before you hear the boot chime. Keep holding until something changes (either you get a boot picker or an OS boots). Note that if there are no bootable volumes, and the CD drive is empty, you might just get a grey screen until you stick a CD in. A little non-intuitive, but that's how it works.

Also, are you using an Apple keyboard or some 3rd party one? If you're using a third party one your control keys might be remapped to something else. Try holding down the Windows key if you have it, or even control. One of them should work.

Finally, even if Ubuntu somehow did what it can't do (mess up EFI), you can reset everything. It's just a pain in the ass. I have over 200 macs I help maintain at work, and even I only get this key combination right 50% of the time.

If that doesn't work, then reset the SMC.
posted by sbutler at 9:12 AM on January 11

Thanks for your continued help, sbutler. Believe me, I tried every combination over and over again--it just doesn't respond. I tried holding the keys down even before I turn it on. I tried hitting it immediately after turning it on. I tried tapping it. Nothing works.

I even tried resetting the PRAM and NVRAM, but since the keyboard just doesn't seem to register, of course that didn't work either. The only thing that works is the Ubuntu LiveCD and holding down the mouse button to eject the disc.

As for the SMC, I have a Mac Mini (Intel), so I'm not sure how to go about doing that given that the instructions were for a MacBook.

And, FYI, I have a Mac keyboard plugged in to the USB port.
posted by war wrath of wraith at 11:05 AM on January 11

The there's something else going on that I can't figure out over the internet. Sorry!

EFI will load and present a boot picker (if you hold down option) no matter what's been done to the HD. I've brought it up on systems w/dead HD's, and even on systems with no HD's! So I really don't see what Ubuntu could have done to your system to fuck it up so bad. I've never seen or heard of a Linux distro that goes around modifying firmware values as part of its install process.
posted by sbutler at 12:24 PM on January 11

Solved. Turns out, it had nothing at all to do with Ubuntu or any boot sector overwrite/corruption. Believe it or not, it was a keyboard problem. Turns out, the thin metal keyboard from Apple has an issue with early generation Mac Minis. It's only recognized after the OS boots up, which explains why none of my key presses were registering.

Once I booted into Mac OS by holding down the 'Option' key (using a different keyboard), I used the Startup Disk utility to set it back to the MacHD. And voila.

To think, I came this close to wiping out my entire system and starting from scratch... Thanks for all the help in any case!
posted by war wrath of wraith at 10:32 AM on January 12