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How to prepare your Mac for sale

Published November 10th, 2012 at 4:18 PM EST , modified November 10th, 2012 at 4:18 PM EST

People sell their computers all the time. Unfortunately for the buyers, this is often done improperly, leaving the buyer with a junk computer that isn’t working properly… sometimes even containing malware! For the seller, such improper preparation is a danger as well, as the buyer may be able to access sensitive data left unknowingly on the machine. Proper security is important to both parties. (As the seller, you may not be terribly concerned about the buyer’s feelings, but keep in mind that the price you get when selling on sites like eBay can depend on how satisfied previous buyers were with you as a seller.) With just a little work, you can clean the machine up, preventing all of these issues, prior to sale.


The first thing you need to do, as the seller, is deauthorize the computer from any systems that only allow you to use a certain number of machines and track which ones you are using. One example is iTunes. If you have purchased music or movies from the iTunes Store, you can play them only on machines that have been authorized by your account. Before selling, you will want to deauthorize the computer. (In the case of iTunes, you can deauthorize all devices, without having access to all of them, then re-authorize the ones you still own. However, you can only do this once per year. It’s easier to just deauthorize in advance, by opening iTunes and choosing Deauthorize This Computer from the Store menu. Other companies may also track which machine their software is installed on and will not allow you to install that software on a new machine without first deauthorizing the old one. You will need to check to see how each such app handles such things. (Fortunately, most do not use such a system.)

Back up your data

Next, you must, of course, make good backups of the data on your computer. One backup will not do… you should have a minimum of two separate backups, on separate physical media. You don’t want to finish this process only to find the hard drive containing your one and only backup has died! For more information on backing up your computer, see my Mac Backup Guide.

Determine what system to install

Once your machine is deauthorized and the data is safe, it’s time to wipe it clean and reinstall a fresh copy of the system. Before you start this process, you need to ask yourself: what system do I want to install? Keep in mind that you do not want to install a system that you are not willing to legally transfer to the new owner or that is linked to you in some way. The general rule of thumb is to reinstall whatever system the machine originally shipped with. For example, if the machine shipped with Snow Leopard (Mac OS X 10.6) and you have upgraded it to Mountain Lion (Mac OS X 10.8), you will want to reinstall Snow Leopard from the original discs the machine came with. The one acceptable exception to this rule is if you are willing to include the newer Mac OS X install disc as part of the sale, which you should only do if you don’t have any other computers using that system. It’s important to understand that this only works with systems that came on physical media. If you have upgraded to Mountain Lion, for example, that system is permanently associated with your Apple ID, and you cannot sell the machine with that system installed.

Erase the hard drive

Once you have decided what system to include, how you proceed depends on the system. If you plan to install Snow Leopard, or any previous system, insert the Mac OS X install disc and restart the computer. Hold down the ‘c’ key as soon as you hear the chime, then let go when you see the Apple logo. The system should eventually boot into the installer, where you first must choose a language. Pick your language, not the buyer’s (unless you know what the buyer’s language is and can read it). Next, choose Disk Utility from the Utilities menu.

If you plan to install either Lion or Mountain Lion (which you should only do if that is the system your machine had on it when it came out of the box), restart the computer and hold command-option-R as soon as you hear the chime. When you see the Apple logo, you can let go. This will start the computer in internet recovery mode, so you will have to have a good internet connection. (Later in the install process, you will need to download about 4 GB of data, so be sure your internet connection can handle that.) Once you have fully booted into recovery mode, open Disk Utility.

Once in Disk Utility, you need to select your hard drive in the list and select the Erase tab. Select “Mac OS Extended (Journaled)” from the Format pop-up and name it something innocuous (like “Macintosh HD”). Next, click the Security Options button. What you see will depend on your system, but there will always be four options: a non-secure erase, one that writes zeros over your entire hard drive and two more that write random data across the entire drive in multiple passes. In Snow Leopard or before, this will take the form of four radio buttons, of which you can choose Don’t Erase Data, Zero Out Data, 7-Pass Erase and 35-Pass Erase. In Lion (Mac OS X 10.7) or later, it will take the form of a slider with four positions, Fastest at the left end and Most Secure at the right. In older systems, 35-pass erases are just frankly ridiculous, and don’t really do any better than a 7-pass erase; do not use that option. On newer systems, the last two positions on the slider are 3-pass and 7-pass erases. The more passes you use, the safer you are, but you shouldn’t need more than a zero erase unless you’re trying to hide important government or industry secrets that may be worth a lot of money to access. Select the appropriate secure erase for your needs, then click the Erase button. And go read a book or something, as it’ll be a while.

Why bother with a secure erase? Because the buyer can use file recovery software to find any files that may still be on the drive somewhere, and some of those files may contain important data. See Recovering deleted files for more information about this.

One important thing to note is that all this is irrelevant if your computer has a solid-state drive (SSD). Such drives have load-balancing firmware, as flash storage wears out with use. The firmware tries to ensure that all areas of storage are used equally, so that particular areas don’t wear out prematurely. Unfortunately, this means that an SSD cannot be securely erased. When Disk Utility tries to write data over the entire drive, the SSD’s firmware will write that data where it chooses, and that may mean that some portions of the SSD remain unerased, and thus may contain recoverable data. If you have sensitive information on an SSD, you should probably replace the SSD with a new one before selling, or simply not sell the computer.

Install the system

Once the erase is finished, quit Disk Utility and proceed with reinstalling the system. Eventually, the system will get to a point where the Setup Assistant will open, allowing you to set up the new system. At this point, quit Setup Assistant and shut down the computer. This way, when the buyer turns on the computer for the first time, it will act like a new machine, and will allow them to go through the setup process themselves.

Pack the box

Finally, keep in mind that you need to include any physical Mac OS X install discs in the box when you ship it to the buyer. You should always include the two gray discs that came with the machine. This is important, even if you are also including a newer install disc, because the second gray disc contains the copies of the iLife apps that came with the machine. If the buyer wants those apps, he or she will have to purchase them separately if you don’t include this disc. If you can’t find both of those discs, do the right thing for the buyer: contact Apple and order replacement copies, which will only cost a small shipping & handling fee. Remember, the happier you make the buyer when selling through sites like eBay, the easier future sales are likely to be!

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  • Al Varnell says:

    There has been a lengthy discussion about the transfer of systems today on an e-mail list I subscribe to. Seems the EULA hasn’t been completely updated to fully explain the user’s responsibilities with regard to Lion and Mountain Lion. Your explanation is absolutely correct in that they are associated with your Apple ID, so there would be no way to restore it should the new user need to. I suspect Apple has so more work to do in this regard.

    • Thomas says:

      As I understand it, the version of Lion or Mountain Lion the machine shipped with is not actually associated with an Apple ID. So, when you boot into internet recovery mode (as opposed to booting from the recovery partition hidden on the hard drive) and reinstall the system that the machine shipped with, you should be reinstalling something that is not associated with your Apple ID.

  • Someone says:

    Just wondering: If your computer’s original OS is incredibly old (Tiger) and you upgraded it to Snow Leopard a few years ago, and never re-upgraded it to Lion or Mountain Lion, can you keep it on Snow Leopard?

    • Thomas says:

      You can only install Snow Leopard as part of the sale if you include the Snow Leopard install disc with the computer when you sell it. Otherwise, it’s a violation of the license.

  • Someone says:

    Didn’t mean that. You said “The general rule of thumb is to install whatever system the machine originally shipped with.” Does that “rule of thumb” apply when the original OS is so old that the new owner wouldn’t be able to do much with it?

    • Thomas says:

      That rule applies always, unless you have installed Snow Leopard or earlier and are willing to include the disc for that system with the sale. If you aren’t willing to include the disc, you can’t legally sell the machine with that system on it.

  • Someone says:

    All right, thanks.

  • KJT says:

    I purchased a new MacBook Pro from and Apple sent me an email asking if I want to sell them my old computer. I answered the few questions and they said they will pay around $500 if the MacBook Pro is on good condition. it has those locks on some areas and they said in their email to make sure all codes/locks are off. However, I can’t set them to be off because they have a combo. Would I erase the HD like you mentioned in your article above and send them the MBP with the disks, or should I install Snow Leopard back on the HD before I send it to apple?

    That is what you meant by installing the OS that came with the computer? Just installing the disk that came with the computer and not the updates, right?

    • Thomas says:

      I’ve never heard of Apple doing that before. Are you certain the e-mail is really from Apple? If so, I doubt it really matters if you reinstall the system properly… they’ll either recycle or refurbish it.

    • Thomas says:

      @KJT, I have done some checking, and nobody I know has ever heard of Apple sending an e-mail asking you to sell your old computer. They do offer a recycling program:

      I would not try to sell to anyone who is soliciting via e-mail, no matter how convinced you are that it is Apple who is asking.

  • KJT says:

    Yes, I purchased a new computer from apple online, and the next day I got an email from apple for the applecare, one for the One to One, and one from Recycle your Apple computer that looks exactly like the other emails. It walks me through a short web questionnaire where I answer various questions about the computer and at the end it give me a price if indeed all the information I provided is true, offers me if I want a check or an Apple gift card, and what I do if indeed I do want to go ahead with their offer. The only area they talked about was making sure that all locks were taken off or unlocked it did not even mention that the HD needed to be erased and the OS put back on the machine, but I really would feel much better if I erased the HD. I think they know that I purchased the MBP from them, they know that it was not that long ago and most likely is still in pretty good condition, since I did not use the applecare over the 3 year period hardly at all. But as I said they are the ones who make the final decision. when I purchased my last MBP for a new one I did not get this option or interest from Apple. I just found it interesting that they leave very little instructions about what they want me to do to the HD before I send it in to them after they send me all the packaging. My question was what I would need to follow to wipe out the entire HD and anything else. Being a novice at this stuff, I do not have any idea what I would need to wipe clean, if it is only the HD, but now that you are skeptical I doubt you will give me any additional advice. That is cool, we all are skeptical at various times in out lives. I do want to add the full 16 GB of RAM so I wish I could use the RAM to help me accomplish this, but I guess I need to get the 8 GB x 2 of RAM and insert it myself or take it to an Apple retailer, if that is what they are called.

    • Thomas says:

      It sounds like this e-mail may have simply been a generic message from Apple advertising the availability of their recycling program. If so, and if the link takes you to an site, it would be perfectly safe to take advantage of that. You would, of course, want to erase the hard drive securely before sending it off, but wouldn’t need to worry about installing a system on it.

  • Dave says:

    I have a 5 month old iMac Mid 2011(originally purchased in July 2012 new) that I bought that I am not thrilled with, and am planning to sell to a friend. I would like to erase the hard drive to make it like it was when it was new. I don’t have the original discs as I bought it from another not so happy owner and he didn’t send them. What do I have to do? I know about erasing the drive in the system utility, but is the restore software on the hard drive, or do I need the discs? It is running Os X 10.8.2. Thank you for your help.

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