Follow these instructions step by step to prepare a Mac for sale:
Step One - Back up your data:
A. If you have any Virtual PCs shut them down. They cannot be in their "fast saved" state. They must be shut down from inside Windows.
B. Clone to an external drive using using Carbon Copy Cloner.
1. Open Carbon Copy Cloner.
2. Select the Source volume from the Select a source drop down menu on the left side.
3. Select the Destination volume from the Select a destination drop down menu on the right
4. Click on the Clone button. If you are prompted about creating a clone of the Recovery HD be
sure to opt for that.
Destination means a freshly erased external backup drive. Source means the internal
Step Two - Prepare the machine for the new buyer:
1. De-authorize the computer in iTunes! De-authorize both iTunes and Audible accounts.
2, Remove any Open Firmware passwords or Firmware passwords.
3. Turn the brightness full up and volume nearly so.
4. Turn off File Vault, if enabled.
5. Disable iCloud, if enabled: See.What to do with iCloud before selling your computer
Step Three - Install a fresh OS:
A. Snow Leopard and earlier versions of OS X
1. Insert the original OS X install CD/DVD that came with your computer.
2. Restart the computer while holding down the C key to boot from the CD/DVD.
3. Select Disk Utility from the Utilities menu; repartition and reformat the internal hard drive.
Optionally, click on the Security button and set the Zero Data option to one-pass.
4. Install OS X.
5. Upon completion DO NOT restart the computer.
6. Shutdown the computer.
B. Lion and Mountain Lion (if pre-installed on the computer at purchase*)
Note: You will need an active Internet connection. I suggest using Ethernet if possible because
it is three times faster than wireless.
1. Restart the computer while holding down the COMMAND and R keys until the Mac OS X
Utilities window appears.
2. Select Disk Utility from the Mac OS X Utilities window and click on the Continue button.
3. After DU loads select your startup volume (usually Macintosh HD) from the left side list. Click
on the Erase tab in the DU main window.
4. Set the format type to Mac OS Extended (Journaled.) Optionally, click on the Security button
and set the Zero Data option to one-pass.
5. Click on the Erase button and wait until the process has completed.
6. Quit DU and return to the Mac OS X Utilities window.
7. Select Reinstall Lion/Mountain Lion and click on the Install button.
8. Upon completion shutdown the computer.
*If your computer came with Lion or Mountain Lion pre-installed then you are entitled to transfer your license once. If you purchased Lion or Mountain Lion from the App Store then you cannot transfer your license to another party. In the case of the latter you should install the original version of OS X that came with your computer. You need to repartition the hard drive as well as reformat it; this will assure that the Recovery HD partition is removed. See Step Three above. You may verify these requirements by reviewing your OS X Software License.
Kappy has explained in detail about restrictions on providing YOUR purchased copy of Mac OS X to a subsequent Buyer. That may be a violation of your license agreement, which may be a problem for you.
From a completely technical point of view, you could present it with YOUR copy of Mac OS X on it and tell the Buyer they need to buy their own copy Immediately. The rest of this writing describes how to remove all traces of your files Without re-installing:
Mac OS X is a Multi-User system. It keeps all the System files in separate protected Directories. It keeps all the User files and User preferences in folders with your login_name under the Directory:
/Users ... (the slash means starting from top-level)
To use the system at all, the new buyer would need to have an Admin user.
1) Use system preferences > Accounts ...
System preferences > Users & Groups ... (in later versions...)
...to create a new Admin User. Write down the name and password
2) Log in using the new Admin user name and password
3) delete all the old accounts and their files. This marks all your files as "erased", but does not write over the data blocks of the files.
4) empty the Trash
5) launch Disk Utility and select the main Volume on the Boot drive, typically "Macintosh_HD"
a) chose Erase tab (Remain Calm. You cannot wipe out the running Mac OS X partition.)
b) click Security Options, and choose one click to the right from the default (this would be Zero out data, one pass)
c) Click (Erase Free Space) This will write over all the files previously marked as erased
6) Done. be sure to send the buyer a note that they need to buy their own copy of Mac OS X RIGHT AWAY, and the Username and password of the temporary Admin user you created.
If they do not buy a their own copy of Mac OS X, and the Mac OS X on the machine gets damaged, they will not be able to re-install. They will need to visit the Genius Bar and answer a lot of questions.