When you are done, you will be directed back to the OS X Utilities dialogue.

Note: Do this with caution and make sure you have already backup all important files and data as there will be no way for recovery from this point onwards.

Click the Erase button button and everything (including files, applications, settings, etc) in your Mac will be completely deleted.

At the Disk Utility screen, select your Mac’s hard drive, then click Erase tab and select Mac OS Extended (Journaled) as format.

You will then be taken to the OS X Utilities dialogue box.

When you see the screen in the screenshot below, select Mac OS X on the right.

Restart your Mac, hold down the Option key when you see the Apple logo.

Now, we will attempt to remove everything from the current OS and reinstall a new copy of OS X Mountain Lion. So we’ve downloaded a new copy of Mountain Lion, copied it over to the USB drive and made it bootable. The installation may take about 10 – 20 minutes and once it is done you’ll have yourself a USB drive with a bootable Mountain Lion. Drag the formatted drive from the left menu to the Destination field, then drag 'Mac OS X Install ESD' on the left menu to Source and click the Restore button.

Now, we are going to create a bootable OS X Mountain Lion in the USB drive.

Once the USB drive is formatted, re-select the formatted USB drive from the left menu, and click the Restore tab.

Keep a backup of the files within if you still need them, then come back to this section. Note: This will remove everything in the USB drive. Under Erase tab, select Mac OS Extended (Journaled) format and click the Erase button.

Select the USB drive on the left menu, Erase tab.

Plug your USB drive into your Mac and launch the Disk Utility application.

Double-click InstallESD.dmg to open (or mount) it on your Desktop.

Navigate to Contents > SharedSupport, then look for the filename 'InstallESD.dmg'.

Look for the file called 'Install OS X Mountain Lion', Right-click and select Show Package Contents.

Create bootable OS X Mountain LionĪfter your download is done, let’s proceed to making a bootable USB drive with your OS X Mountain Lion in it. Note: This may take up between 10 and 60 minutes, depending on the speed of your Internet connection. If you’ve previously purchased a copy of Mountain Lion, don’t worry, you will not be recharged.

Re-enter your App Store credentials if required.

Look for OS X Mountain Lion, hold down the Option key and click Download.

Launch the App Store and go to the Purchases tab.

Here’s how you can download and obtain a soft copy of Mountain Lion. The installer you downloaded from the App Store automatically deletes itself after you’ve successfully upgraded (or install) your Mac. Re-download Mountain Lion Installerįirst, grab hold of a copy of the Mountain Lion installer file. While I was doing maintenance for my OS X, using the Maintenance app, the app told me that.

Clean install on macbook os x 10.7 lion