A process window, like the one below will be displayed in Terminal.

Sit back and wait many hours for the hard drive to be securely erased.

Listed below are the various Levels permitted, from 0 to 4. Important Note: For a detailed explanation of this command read this article at OS X Daily about erasing free space from the command line. Type diskutil secureErase freespace 2 /Volumes/Macintosh HD (or replace Macintosh HD with the precise name of your Mac’s hard drive or replace 2 with another “Level”, see guide below) and then press the Return key.Only proceed if you’re comfortable using Terminal. One small typo could lead to the unintended loss of data or lose.

Issuing commands requires precision and is unforgiving. Be careful when issuing commands from the Terminal. Click on the Utilities menu and select Terminal.You’ll be returned to OS X Utilities window.Click on the Disk Utility menu and select Quit Disk Utility.You’ll be asked if you’re sure you want to erase it.In the right pane of the Disk Utility window, click the Erase tab.In the left pane of the Disk Utility window, click on Macintosh HD (which is your laptop’s internal hard drive).Click on the Disk Utility option from the “OS X Utilities” window.Give your Mac a couple of minutes to startup, at which point you’ll see a window like the one this one.Once you see the Apple logo appear in the middle of the screen you can release the Command and R keys.This instructs the computer to startup from the Recovery Partition. Turn on the laptop and immediately press and hold down both the Command key and the R key.

Erase macintosh hd