HowTo revert new MacBook Pro, Mac Pro or iMac to Snow Leopard

Hi Steve,

Now to my question: Can I completely erase all possible artifacts from the disk, like it was new from the factory, so i can repartition and reinstal OSX?

short answer to your question: yes, easily.

Cattus Thraex has already provided the methodology, here I'll expand in case you or another wants a step-by-step.

Erasing the disk is actually fairly easy, once you have another disk from which to boot the computer. Your iMac8,1 is an Early 2008 model, I believe, that was delivered with OS X 10.5.2 or 10.5.4. In those days, computers were delivered with optical disks containing the appropriate version of the OS.

basically, you need to create a new partition, overwriting all/any existing partitions. This will render data on the old partition(s) effectively unaccessible. Have backups, clones, and Time Machine repositories available. If returning to older version of the OS than the Time Machine repository was written with, you might want to retrieve a Time Machine snapshot to an external disk....

assuming you have those disks:

1. Insert the Install disk
2. Reboot the computer to the optical disk (restart & hold the C key, or just double click on the "Install OS" type of icon in the mounted disk)
3. proceed past the language screen, until you get to the screen where one starts the installation process
4. at this point, pull down the Utilities menu and select the Disk Utility
5. in the left side of the window, select the internal disk to wipe. Select the disk, not the Volume
6. click on the Partition tab in the main portion of the window
7. change the pull-down menu from "Current" to "1 Partition"
8. enter the name you want in the namiing field - this can be changed later, so not critical now
9. select Mac OS Extended (Journaled) as the Format, unless you have good reasons to do otherwise
10. click the "Options..." button, and choose "GUID Partition Table"
11. then click "Apply"

This will leave you with a disk that still has the data on it, but the "Table of Contents" and "Index" to all that data is erased. Effectively, normal users and the new system have no way to access that info.

This is really all that is necessary for your expressed purposes. You can then safely quit the Disk Utility, and either proceed with installing the original 10.5.x system, or quit the installer and boot from another install source to install other systems....

If you were giving the computer to some one else and were concerned that they would maybe dig beyond the partition map and look at the raw data bits, you could bury them deeper under a layer of Zeroes written across the entire disk. On my systems this takes about 7 hours for a 1 TB drive.. If desired, let me know and I'll write up the simple 1-2-3 for it.

if you don't have those system disks, you can clone your existing system to an external disk, using tools like SuperDuper! or Carbon Copy Cloner. After the clone is ready, point to it as the Startup Disk (in System Preferences). Reboot, and then proceed with the Disk Utility to create a new single partition on the internal hard disk.

cheers,

Roy

Hi SteveBel,

Any thoughts?

well, yeah. My first thought is that your stated objective is to clean all existing partition information from your internal hard disk in your iMac, "like it was new from the factory".

Regardless of what you now see with diskutil (or fdisk, for that matter), that will all be gone if you follow the suggestions from Cattus Thraex or myself.

so, why worry about what kind of partition information is now stored in the partition map(s)?

from your diskutil output, your disk0 has the standard partition layout for a 320 GB hard drive with Lion or Mountain Lion installed, complete with the Recovery Partition. Mine looks the same, except that I have a 250 GB partition for my disk0....

from the man page, fdisk is a DOS partition maintenance program. Perhaps a leftover from Boot Camp days on your machine.... If you are using the fdisk utility currently, I suspect this is some of the issue you have with partitions coming and going, and difficulty booting at times. AFAIK, which isn't that far in this case, for a system setup such as that displayed in your diskutil output, one has no business messing around with fdisk at all. BIOS and Master Boot Records have no place on a Mac OS X system, except perhaps when a Boot Camp partition is present. Never played with Boot Camp myself....

so -

- backup your data

- boot of an independent system disk

- partition your internal disk in a single partition, using the full size of the disk, whether that is 320 GB or 500 GB or larger

- ensure that it is OS X Extended (Journaled) and using the GUID Partition Table

- install your favorite version of Mac OS X

- restore your data and applications, or start with a fresh slate

and you are good to go!

cheers,

Roy

in my humble opinion, you are making this too hard.

repartition your entire disk with Disk Utility, as described, and don't run fdisk any more!

cheers,

Roy

Steve,

the rm -rf command will only remove files and directories in the root filesystem (/).

it will not affect any other partitions.

run the command: df -h

and you will see which partition is mounted at root (/).

in your case, the filesystem /dev/disk0s2 is likely mounted on /

cheers,

Roy

Hi BigBongo -

I do not recommend downgrading to Snow Leopard (10.6.x), or any earlier version of the operating system, for any Mac computer that had its initial release after Lion (10.7.x) was released (mid-summer 2011, I believe).

The reason for this is that it is likely that hardware designed, configured, and built after development of Snow Leopard will have hardware components for which there are no drivers in the Snow Leopard OS. The further the design and build dates of computers move away from the end of Snow Leopard development, the greater the divergence of hardware components from the driver set included in Snow Leopard.

This thread began because I ordered a MacBook Pro that summer, that was advertised as shipping with Snow Leopard. Between the time the order was placed, and the computer imaged with a version of the OS, Apple had released Lion (10.7.0). Even though this was only a few days between order and ship, the MacBook Pro arrived with Lion installed.

What made "The Procedure" viable, was that there were no hardware updates to the MacBook Pro being delivered with Lion installed. Therefore, all the drivers for that computer's hardware existed in Snow Leopard 10.6.8 (but not earlier OS versions of 10.6.x).

At this time, I'm transitioning my group to Mountain Lion (10.8.x), and our new computers we order will be left running Mountain Lion. I've been working with it for a while on my desktop and laptops, and, although I had to change a few things, I can pretty much work with the same workflow I previously used. I had to jettison FruitMenu, one of my all-time favorites. Now I see there are other options to provide similar functionality...

So, that is my advice - worth every penny you didn't pay for it. 😉

Now, to answer your questions:

- I can't help you, at least with information from my own direct experience, as I have not, nor will I, take a late model computer and put Snow Leopard on it.

- Yes, I believe a partition could be created, and Snow Leopard 10.6.8 installed, using "The Procedure" from this thread

- To make all the components of your hardware work with the SL 10.6.8 operating system, I believe you would need to find the kernel extensions and drivers currently shipping in Mountain Lion that do support your hardware, and copy them from the Mountain Lion System directory to the Snow Leopard System directory.

- it would not surprise me that those drivers might need other supporting files transferred from the Mountain Lion System as well. I have no idea which they would be.

if you are interested in pursuing that quest, I've seen other discussions where people are making attempts to do so. One such thread is: https://discussions.apple.com/thread/3189463?start=0&tstart=0 , although that thread is not very technical. There are others, specifically dealing with MacBook Air and iMacs, as the hardware of those two models were changed along with the release of Lion, so those and later versions never had a version of Snow Leopard with the complete set of drivers for that hardware.

so, sorry I'm not providing what you would like, but we do have to keep moving on with operating systems and hardware development. On the whole, we keep coming out ahead - but there are warts and boils along with the gold and silver.

cheers,
Roy