After setting up my new one-size-fits-all MacBook Air/Cinema Display desktop, I turned my mind to clearing out the iMac for sale.
This machine has been running very successfully from an external Thunderbolt SSD for the past six months. The speed increase over the standard internal 7,200rpm hard disk drive was dramatic and well worth the upgrade.
First step was to disconnect the LaCie drive, but only after setting the iMac to boot in future from its internal disk. Do this from System Preferences/Startup Disk.
The trouble was, the iMac just wouldn’t boot. Repeated attempts resulted in worrying system code appearing in the top left of the screen. I suspect that the update to Mountain Lion had left the system on the iMac in an unstable condition. It had not been booted from the internal disk since the update.
No problem, I thought. Boot from the recovery partition (which has taken over from boxed disks) and I can wipe the main drive and reinstall a clean copy of Mountain Lion. There was a problem, though. I could not find the recovery partition, despite holing down ⌘R during the boot process.
Fortunately I had a cloned backup in the form of the LaCie SSD which had been used for months as the main drive. I rebooted to the LaCie (holding down to Alt (⌥) key when switching on; this allows a choice of boot drive). I was then able to clone the disk back to the iMac, using Carbon Copy Cloner. Once this had completed I could boot the iMac independently.
My ultimate objective in all this was to use the iMac’s recovery partition (introduced with Lion in mid–2011) to wipe the main volume and install a clean version of Mountain Lion.
Because the Mountain Lion installation file is deleted after use, I re-downloaded Mountain Lion to the iMac from the App Store in the hope that a fresh installation would re-create the recovery partition. It didn’t, but for the very good reason read on.
Next thought was to use the new Internet Recovery system to download the original OS and perform a clean install. But while researching this I came across an interesting paper on mid–2011 computers without a recovery partition. It seems that some machines, capable of hosting the recovery partition but lacking one, were produced in the period leading up to the introduction of Lion. Among them was my iMac.
Secret: Firmware update
This was worth a try, so I found the specific firmware update for the mid–2011 iMac. As soon as this was installed the recovery partition miraculously appeared. It was then a simple task to wipe the main volume and install a clean copy of Mountain Lion.
Then it struck me, while thinking about the time last year when I bought the computer. I suddenly remembered that the new iMacs had been introduced just before the launch of Lion and mine had in fact been supplied with Snow Leopard. I remembered I had purchased and installed Lion a week or so after the buying the machine. Pity I hadn’t remembered this a few hours before.
This explains the absence of the recovery partition, although the ability to install the enabling firmware update retrospectively was a welcome lifesaver.
I still have not dragged the big box out of the loft. If I am true to habit I should find the Snow Leopard disk in that box. That would have avoided hours of work and research. I could have reinstalled Snow Leopard and handed over the iMac in its original state.
Back to basics
It turns out that this is what Apple expects, indeed mandates. If you have updated the OS you must (legally speaking) downgrade it to the original before sale. In the old days this was simple: Just use the original disks to reinstall the old OS. Now it isn’t so easy and, I suspect most people do not bother. They just sell the machine with the currently installed OS. No doubt some sell with all their data still on board, including difficult-to-guess passwords such as 12345. As you gather, I am made of sterner stuff.
In my case, I am selling the iMac to a friend who has an Apple ID and also owns a copy of Mountain Lion. So, to keep Apple happy and avoid future ID problems, I used his credentials to download and install my friend’s legal copy of Mountain Lion.
All’s well that ends well, but this hitch in proceedings took several hours and much research. The moral of the story is to check the status of your computer and sort out that recovery partition, if possible, well before sale time. If you bought around the middle of 2011 and have no recovery partition you can install the enabling firmware update.
Installation drives and backups
It is also wise to create an external bootable OS X installation disk. Use a spare external hard drive or, even a USB flash drive. But go for at least 6GB to be on the safe side. If your internal hard disk fails catastrophically you may not have access even to the recovery partition. In such a case an external boot drive is a lifesaver.
In the event of a complete failure of the internal disk, though, the best recovery option is a regularly updated bootable clone of the entire contents of your disk. I would recommend this in addition to Time Machine, which can be also be used for restore purposes but is less satisfactory. As ever, belt and braces is a good plan. You can never have enough backups.
For the ultimate in diagnostic boot disks, read this article by Jordan Merrick in Mactuts+. Creating one of these essential tools takes up around 90 minutes of your time. It is definitely time worth spending and creating one is top of my task list.
by Mike Evans, 3 October 2012