What to Know

• Restart the Mac from the bootable installer while holding down theOptionkey.Selectthe installer on the USB driveandpressReturn.
• If installing to startup drive, selectDisk Utility>Continue.Selectthe drive and chooseErase. 
• ConfirmMac OS X Extended (Journaled)is selected.SelectEraseand quitDisk Utility.Select Install Mac OS X>Continue.

This article explains how to perform a clean install of OS X El Capitan on your Mac's startup driveoranother drive.It includes information on the choices you have when you perform a clean install.

How to Perform a Clean Install of OS X El Capitan

OS X El Capitan (OS X 10.11) offers two installation methods.This guide focuses on the "clean install" method.When you install El Capitan on your current startup drive with the clean install method, you erase everything on the drive.That includes OS X, your user data, and personal files.Back up your data before you begin.

After you back up your data, download El Capitan from the Mac App Store.Copy the installer to a USB drive to make a bootable drive if you're installing to the startup drive.

If you're performing the clean install on an empty volume, you can jump to the section titled, "Perform a Clean Install of OS X El Capitan." You don't need a bootable USB drive.

Erase the Startup Volume

After you back up your data and create a bootable USB drive containing El Capitan, erase your Mac's current startup drive by following the steps below.

1. Insert the USB flash drive containing the El Capitan installer into your Mac.

2. Restart your Mac while holding down the Option key to display theOS X Startup Manager.

3. Select OS X El Capitan installeron the USB flash drive and thenpressReturnto start up the Mac from the installer.

4. Before you can clean install OS X El Capitan, you must first erase the current startup drive that holds the older version of OS X.SelectDisk Utility and Continue.

5. In the left sidebar of Disk Utility, selectthe volume you want to erase.It will likely be named "Macintosh HD," unless you renamed it at some point.

   

6. With the proper volume selected, chooseEraseat the top of the Disk Utility window.

7. You'll be asked if you wish to erase the selected volume and given the opportunity to rename the volume.Leave the nameorenter a new one.

8. Just below the volume name field is the format.Make sureOS X Extended (Journaled)is selected and then selectErase.

9. Disk Utility erases and formats the selected drive.Once the process is complete, quitDisk Utility.

10. In theOS X utilitywindow, selectInstall OS Xand then Continueto start the installer

Perform a Clean Install of OS X El Capitan

If you chose to perform a clean install on your current startup drive, then you have already erased your startup drive and started up the installer.

If you chose to perform a clean install on a new or empty volume (not your startup drive), then you're ready to start the installer, which you'll find in the Applications folder.Thefile is labeledInstall OS X El Capitan.

The installation processes are the same going forward for both clean install methods.

1. In the Install OS X window, selectContinue.

2. The El Capitan license agreement will display. If you'd like, read through the terms and conditions. Then selectAgree.

3. Confirm your agreement and selectAgree.

4. The El Capitan installer displays the default target for the installation. If it is correct, selectInstall.

   If it isn't correct, selectShow All Disksand select the correct target disk. ChooseInstall. Enter your administrator password and selectOK.

5. The installer copies the needed files to the drive you selected and then restarts.

6. A progress bar display with an estimate of the remaining time.

   

7. After all the files are installed, your Mac restarts and you are guided through the initial setup process for El Capitan.

Set Up OS X El Capitan

When the installation process is complete, your Mac reboots, and the El Capitan setup assistant automatically starts.Theassistant helps you through the process of configuring your Mac and operating system.

1. When the Welcome screen appears, select which country your Mac will be used in. ChooseContinue.

   

2. Select your keyboard layout and chooseContinue.

3. TheTransfer Information to This Macwindow appears. Here you can choose to move existing data from a Mac, PC, or Time Machine backup to the clean install of El Capitan. Because you can do this at a later date using the Migration Assistant, selectDon't Transfer Any Information Nowand select Continue.

4. Choose to enableLocation Servicesor leave it off and selectContinue. A window drops down asking you to confirm that you do not want to use Location Services. SelectDon't Use.

   Some apps, such as Find My Mac, require Location Services to be turned on. However, since you can enable this service from the System Preferences, it's not important that you enable it now.

5. You are asked whether to add your Apple ID/Apple Account and whether to allow your Mac to automatically sign in to various services upon booting up. You can set the Apple Account sign-in now or do it later from System Preferences. Make your selection and chooseContinue.

6. If you choose to set up your Apple Account, a window drops down asking if you want to turn on Find My Mac. Once again, you can do this at a later date. Make your selection by selectingAllow or Not Now. If you choose not to set up your Apple Account, a window drops down, asking you to confirm that you don't want your Apple Account set to log you into various services. Select eitherSkip or Don't Skip.

7. The Terms and Conditions for using El Capitan and related services will display. Read through the terms and selectAgree. A window will display, asking you to confirm the agreement. SelectAgree.

8. The Create a Computer Accountoption displays. This is the administrator account, so be sure to note the username and password you selected. The window will look slightly different depending on whether you choose to use your Apple Account or not. In the first case, you have the option to sign in to your Mac using your Apple Account. In this case, you only need to provide your full name and an account name.

   The account name will become the name for your Home folder, which will contain all of your user data. We recommend using a name with no spaces or special characters.

9. If you decided not to use the Apple Account or if you removed the check mark from theUse My iCloud Account to Log Initem, then you'll also see fields for entering a password and a password hint. Make your selections and then selectContinue.

10. Select your time zone by clicking on the world map or choose the closest city from a list of major cities around the world and chooseContinue.

11. The Diagnostics and Usagewindow asks if you want to send information to Apple and its developers about problems that may occur with your Mac. The information is sent anonymously. You can choose to send information to Apple, just send data to app developers, send to both, or send to no one. Make your selection, then selectContinue.

12. The setup process is complete. After a few moments, you'll see the El Capitan desktop, which means you're ready to start exploring the clean installation of your new OS.

Why Perform a Clean Install?

The clean install method is a good choice for testing a new OS on a dedicated drive or partition, or when you have been experiencing software related issues with your Mac that you have not been able to resolve. When the problems are severe enough, you may be willing to trade in your apps and data for the peace of mind of a clean slate.

Before you begin an installation, verify that your Mac is capable of running OS X El Capitan.

Types of Clean Installs

There are two types of clean installs you can perform: an install onto an empty volume, and an install on a startup volume.

Clean Install on Empty Volume

This involves installing El Capitan onto an empty volume, or at least one whose contents you don't mind removing. The key point is that you're not targeting your current startup volume as the destination for the clean install.

This type of clean installation is easy because, since the startup drive isn't involved, you can perform the clean install while booted from the current startup drive. There's no special, custom-made startup environment needed. Just start up the installer and go.

Clean Install on Startup Volume

The second option, and perhaps the more common of the two, is to perform a clean install on the current startup drive. Because the clean install process erases the contents of the destination drive, it's obvious that you can't boot from the startup drive and then try to erase it. The result, if it were possible, would be a crashed Mac.

That's why if you choose to clean install El Capitan on your startup drive, there's an extra set of steps involved: creating a bootable USB flash drive that contains the El Capitan installer, erasing the startup drive, and then starting the clean install process.

Back Up Your Existing OS and User Data

By installing El Capitan on your current startup drive with the clean install method, you will erase everything on the drive. That includes OS X, your user data, and personal files.

No matter the method, you should have a current backup of the existing startup drive's contents. You can use Time Machine to perform this backup, or one of the many cloning apps, such as Carbon Copy Cloner, SuperDuper, or Mac Backup Guru. You can even use Disk Utility. Before proceeding with the installation, it's important to take the time to create a current backup.