SecureErase (Category 4 - DoE 3 - Pass Secure Erase) Macintosh HD - in Terminal app

Thanks for your reply and for providing a link to and information about Knoppix, HWTech.

FYI: The hard drive was replaced in 2020.

I appreciate your suggestion, but I'm not comfortable with nor do I have even rudimentary Linux-based knowledge of booting from a Knoppix LInux USB stick without proper supervision.

If something were to happen during the process (possibly making the HD inoperable), that would put me in a far worse position than I'm currently in.

I continue to look for a solution that allows me to use Terminal as it is part of the MacOS.

Up to this point, the overwhelming consensus has been Terminal-avoidance, akin to the third rail of a subway line.

I hope to get a better understanding of why that is and if what I'm seeking can be accomplished successfully.

Thank you again, John.

Performing a level 0 may be adequate for the majority of end-users, but I'm not in that category.

You are correct in pointing out that I eventually intend to sell my iMac, but only after I complete a level 4 Secure Erase procedure on the hard drive.

I want to ensure I've taken the highest level of security available to thwart any attempts to tamper with the hard drive to extract data from it. The odds of that happening are probably highly unlikely, but I'm still going to move forward with the secure erase procedure using Terminal.

And, yes, I could just remove the hard drive and hammer it into oblivion, but that's not what I wish to do.

Thank you for your suggestion, Bob.

I'm going to assume that you've never had an opportunity to remove a hard drive from an iMac. It's a dreaded task even for the most tech-savvy Mac computer technician. I've had many opportunities to watch them do just that, and each time the struggle to open the iMac to access the hard drive was very apparent and eventually accomplished with tremendous difficulty. There was an equal struggle, again with much difficulty, in reassembling the iMac.

So (from my experience) this is definitely not a task for the uninitiated or, for that matter, any average mere mortal.

I have accomplished this same task many times with Windows-based PCs with no problems whatsoever. But getting into one of those systems only involved removing a few screws.

I stand corrected.

Glad to hear you've had positive and successful experiences with cracking open and accessing the iMac's internal components.

It's still not a task I want to perform.

I will move forward with finding someone who can guide me through a level 4 Secure Erase procedure.

When I find that individual and have accomplished the procedure, I will record the procedure here.

Thanks again, Bob and everyone else who took time out from their day to offer constructive suggestions.

It's always interesting to discover just how many ways any one problem can be solved especially when so many individuals can be reached to offer assistance.

Thank you, John.

I tried your suggestion of adding the space after the number 4 : diskutil secureErase 4 /Volumes/Macintosh\ HD

(Please note - this procedure WAS NOT carried out in RECOVERY MODE)

That resulted in the following statement: "Could not find the disk hd".

FYI: When I entered this environment (Recovery Mode), I did not have the option to adjust the security level (akin to being grayed out). I had full control of my mouse, I simply could not adjust the slider control.

The more I progress, the more I seem to be encountering many 'blockades' not customarily seen or experienced by the average end-user or more experienced developers/programmers.

"...never use these options for an SSD as SSDs don't work the same way as hard drives".

In that case, I've come to a dead-end.

Had I known that this particular drive was a critical point to mention from the start, this entire discussion would have ended substantially sooner.

Perhaps that could explain why I got the "Ownership of the affected disk is required." after entering my parameters.

"HWTech: I'm a bit curious about why you did not have Filevault enabled on this system if data security is so important now when preparing the computer for sale."

That was a serious misstep on my part.

Fortunately, I managed to get through that ten-year stretch unscathed.

Regarding all of the information you provided - Thank you for your generosity and for sharing your wealth of knowledge.

I'm a big fan of learning by doing despite the outcome. This experience could not have happened without everyone's feedback/assistance.

At this point, I've got a few options that I can try and see where it leads me.

I downloaded the Magician For Mac software. It's a ZIP file.

However, once the ZIP file is unzipped, the executable file contained within is an .exe file, not a .dmg file.

Why a software company would compress an .exe file and label it as a Magician For Mac ZIP file is beyond my comprehension.

These are the results from the (2) recently suggested parameters spacing (in recovery mode)::

[-bash-3.2# diskutil secureErase 4 /Volumes/Macintosh\HD

Could not find the disk /Volumes/MacintoshHD

[-bash-3.2# diskutil secureErase 4 "/Volumes/Macintosh HD"

A whole disk must be specified when doing secureErase without the

"freespace" option; if you need to wipe a single partition, you must

use diskutil zeroDisk or diskutil randomDisk but you will subsequently

need to reformat (newfs) the partition with "diskutil eraseVolume"

[-bash-3.2#