Erasing Mac OS Mavericks safely for sale

llmdco wrote:

after erasing MacIntosh HD in Disc Utility,

and logged myself out as primary admin such that the buyer will only access through the guest account,

This doesn't make any sense. If the drive was erased without reinstalling macOS then you should not be booting macOS except through Recovery Mode.

Does your Mini have a Hard Drive or an SSD?

If it uses an SSD and you erased (or rather Partitioned & formatted) the whole physical SSD, then your data has been wiped from the SSD due to how SSDs work.

If it uses a Hard Drive, then even if you perform a simple erase the data still remains on the Hard Drive & can be accessed by data recovery software. You either need to first enable Filevault and let the encryption process finish, followed by a simple erase of the physical drive, or you need to opt for the "Secure Erase" option within Disk Utility so that zeroes are written to the whole drive to overwrite all data on the Hard Drive.

If your Mini was working, then why didn't you just create a bootable macOS USB installer while you had the chance? A system running Mavericks can easily run at least macOS 10.11 El Capitan which does have an installer which can be downloaded. If you have access to another Mac with a model generally from 2007 to 2015, then it can be used to make an El Capitan USB installer (there are multiple steps required to extract the real installer into the Applications folder).

Create a bootable installer for macOS - Apple Support

It really helps to know the exact model of the Mac since this Mini may be able to run an even later version of macOS which opens up more possibilities of having a compatible Mac than can create a later version of macOS USB installer. You can get the exact model by clicking the Apple menu and selecting "About This Mac", or if you cannot boot normally, then you can enter the system serial number on the check coverage page here (do not post the serial number on the forum since it is considered personal information):

Check Your Service and Support Coverage - Apple Support

If the Mini was not completely erased and you can still boot into Recovery Mode with Command + Option + R, you can boot the Maverick's recovery mode installer (without requiring authentication with an AppleID to confirm "purchase").

I wouldn't trust it. Plus, they will need to be able to access more than the guest account to create their own accounts on the computer.

There is no Mac on the planet for which Mavericks is the last compatible macOS...why don't you download and create an El Capitan installer and use that to erase and re-install macOS? Or upgrade the OS to El Capitan first and then erase and reinstall from Recovery Mode?

llmdco wrote:

I realized soon after posting this that a step in the sequence was left out. After erasing the drive (which is not SSD), tried reinstalling Mavericks but could not proceed, therefore, I used Time Machine to reboot.

I think if you restore the full TM backup, it will also restore the system files as well, but I'm not certain. I believe this was how the older versions of TM worked. Worth a try if you don't have access to another working Mac for one of the model years listed for El Capitan or High Sierra. I'm not sure how to do that though since I never used TM back then.

Late 2009 Mac mini. Model Identifier 3,1

This model can also run macOS 10.13 High Sierra. This means if you have access to a working Mac model from Late-2009 to 2018, then you can create a bootable macOS 10.13 High Sierra USB installer.

You can confirm which exact Mac models are compatible with various versions of macOS by using this article since the model years I mentioned are just general guidelines since there are some exceptions:

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

Why is there no Mavericks USB installer?

Only Apple knows and they are not telling. Or perhaps Apple is not even aware, they certainly do not care about the installers since one of them has a bug which they haven't fixed in many years....a very simple bug which only requires modifying a single number the installer's configuration file.

A couple of important details are not entirely clear to me.

... After erasing the drive (which is not SSD), tried reinstalling Mavericks but could not proceed, therefore, I used Time Machine to reboot.

If you booted from the TM backup drive, then it invoked its version of Recovery — not the one resident on the (presumably erased) Mini's startup volume. Time Machine backup volumes are bootable only in Recovery.

The reason for asking is that it's not entirely clear to me whether you restored that Time Machine backup or not. Obviously that's not what you would do if you were selling, donating, or otherwise parting with that Mac. You boot the TM backup drive and use its version of Disk Utility to erase the Mac. I assumed that is what you did but I don't want to assume. As an aside, restoring a Time Machine backup also restores the local startup drive's version of Recovery. This is only applicable to those older Macs.

Next important question: Did you encrypt that Mini's startup drive with FileVault? If so you're done. Its data are utterly irretrievable without that FileVault key — which gets erased along with everything else. It's useless.

On the other hand if you did not use FileVault its data are theoretically retrievable, depending on what method you used to erase it and the amount of time effort and expense someone wanted to implement toward that effort.

Lastly, why did you not simply boot from that Mac's original System Install DVD? Those grey discs must accompany the Macs they shipped with from cradle to grave. To properly transfer ownership to a new owner, it's required to reinstall that OS X version. Its new owner would be greeted with the "Hello" language selection screen the same as you did upon initially setting it up.

Personally I would not be interested in buying any Mac that required those discs, unless the seller included them, or unless I happened to have my own copy for that specific model.

That Mac is too old to use Internet Recovery.

HWTech wrote:

llmdco wrote:

Why is there no Mavericks USB installer?

Only Apple knows and they are not telling.

Simple answer, Macs that shipped with optical installation media did not require them. The OP's Mini did.

However, there were a handful of models that were not eligible for Internet Recovery either. Specifically, pre-Retina MacBooks and pre-2011 MBAs with no optical drives, so for them Apple offered a Lion installer on USBs. If not for them OS X would have been impossible to install — "impossible" without NetBoot or another directly-connected, bootable device like another Mac in Target Disk Mode, a hard disk drive... etc.

Thanks. That is helpful information. No, I do not recommend that you sell, give away, donate, "recycle" or otherwise transfer ownership of the Mac in that condition. Encrypting its startup disk with FileVault followed by completely erasing the disk will be a necessity if you want to completely assure yourself its information is rendered permanently inaccessible to anyone sufficiently motivated to do such things.

Or, remove its hard disk drive and physically destroy it.

I am making that statement predicated on what you originally wrote: "Are these enough safeguards against someone accessing any personal information I may have left in there." The only technically correct answer to that question is no.

Next, if you no longer have its original installation media, the marketability of that Mac becomes limited to those with the technical knowledge to install an operating system and make it useful again. It doesn't have to be an Apple operating system. Those with such knowledge will not be willing to pay much for it, if anything. They are typically found in thrift stores, at a garage sale, or in the trash. That does not mean they are literally trash, but that old Mini would be best suited for a hobbyist or someone with similar interests.