Mac OS X:Clean Install – The Easy Way

Confused Emoticon
Who knew???


Confused Emoticon
What just happened to my Mac?

I installed Yosemite (10.10), on my 2008 iMac. I loved the look of this new operating system, and its features; however, after the install, my iMac was running pathetically slow. I spent hours trying to debug the thing, and could not find a single cause. I knew that over a number of years I had installed many successive versions of OS X, one on top of the other, on my iMac, and adding to that, several years of code from long since deleted programs were still floating around in my system files. I reasoned the combination of the residual affects of software remnants were more than likely the cause of the slow performance I was seeing on the iMac. The only cure: a clean install.

So what is a clean install? Simply put, with the exception of a newly installed operating system, the computer’s hard drive is empty, – clean, just like it was the day the computer was purchased.  After a clean install, all that is needed is to restore the data, and favorite programs, and the computer should be in top running shape (baring any unforeseen hardware problems).

I have done clean installs on a several Macs. The process is pretty simple. Aside from making a copy of any data that needs to be reinstalled, and the real installation of the programs, the Mac does all the heavy lifting. All you have to do is know where the proper “buttons” are located, and when to push them. The clean install process being explained in this article is pretty straight forward, not very complex, and isn’t too original. In fact, it has been available to Mac users for a number of years.

Lets get started…..(Note:  For instructions on installing OS X on a NEW hard drive, click here)


The very first thing to do is to see if your current Mac has the hardware necessary to run your new operating system. Apple is very good about letting you know the system requirements for their operating systems. An example of Apple’s requirements for Yosemite can be found here.

A necessary step in this process will be to totally erase and reformat your hard drive. So now is the time to back up any data (documents, music, photos, movies, etc.) on your computer that you wish to keep. You might be doing that now with Time Machine; however, if the Time Machine backups are on the same drive that you are using, you will want to make a backup to another drive. In this instance, an external USB hard drive will work fine. If your computer is on a network, you can also backup your data to another computer using “rsync” (for more information on “rsync”, and how to use the program, click here).

Now, make sure you have all the programs you wish to install at your disposal, i.e., gather appropriate DVDs, CDs, and/or program download IP addresses. For programs you have installed from the App Store, you can find them to reinstall by opening the App Store application, and once opened, clicking on the Purchases tab at the top of the program.

Next, if you are not using a password manager like LastPass, find out how to make a copy of stored passwords from your web browser (a web search with referral specific to your favorite browser will give the desired results). Note: If you are currently synching your browser’s passwords, browsing history, etc. with other browsers, you do not need to perform this step.

Verify that you are using IMAP for any mail client (this way, when you setup Mail, or whatever client you use, your email will once again be populated).  You can find more about IMAP by clicking here.

Finally, check and see if there is anything else you need from your hard drive, and save it to another device or computer.

Get’er Done

What follows is Install Plan A. I never like to leave much to chance, so I strongly suggest you have an Install Plan B. Have a copy of Snow Leopard 10.6 (or later version of OS X) on a USB drive, or a DVD. If for some reason, the OS X System Recovery process (Install Plan A) fails, you simply install the older version of OS X from the DVD or USB drive, and once installed, download the newer operating system from the existing operating system’s App Store program. Note: As an option, you can also install the most current version of OS X on a USB drive or DVD, and from either of those install the “new” OS X on your target drive. I prefer to use this option as Install Plan B, because the are too many things that can go wrong in its implementation (Find out how to install OS X by using a USB Drive by clicking here,  To install by DVD, click here.)  In Install Plan A, the newest version of OS X is downloaded from Apple, and seamlessly installed. Simple, and with less chance of error.

Here is Install Plan A:

There are a number of things you can do by holding down specific keys when your Mac starts up (you can see the entire list here). For our purposes, from a Mac that has been turned “off”, depress the “start” button, and after the start-up tone plays, hold down both the Command and R keys. Keep both keys depressed until the “Apple” logo shows up on the screen, or a sliding bar appears (depends on the operating system). Once all the “start-up” activity is completed you will be in the System Recovery area of OS X.


OS X Restore Utilities
Figure 1.

You should be looking at a window named OS X Utilities (see Figure 1).  Click the Reinstall OS X icon. At this point, if a new version of OS X has just been released, you will see its predecessor (such as: when Yosemite was initially released, for several days, Mavericks was the only operating system available to download and install from the System Recovery area. This is, I suppose, to allow people that installed the “new and latest” version of the OS to downgrade to the previous OS, should the user be unhappy with the newer operating system). It is now decision time for you: Install the “older” operating system and download the newer version of OS X from the App Store, or wait a few days, do the same check, and install the newest version OS X when it becomes available. If you decide not to install any version of OS X at this time, cancel out, and reboot your computer. You have made no permanent changes. When you decide to continue with the install, again enter the System Recovery mode, and do the following:

Click the Disk Utility icon. From here, follow these steps:

OS X Disk Utility Erase Drive
Figure 2.


In the left-hand side bar, click on your main hard drive.
Click on the Erase tab. Make sure in the Format field that Mac OS Extended (Journaled) is selected.
Usually, the Mac provides a name for the hard drive, if not or you want a different name, enter it in the Name field.
If proper, say a few prayers to your deity, and click the Erase button at the lower right side of the window.
Next, click out of the Disk Utilities screen. You will now be back at the OS X Utilities screen.

OS X Elgibility Screen
Figure 3

Now click the Install OS X icon and follow the instructions on the screen. The operating system will be downloaded and installed.

Yosemite Reinstall Screen
Figure 4.

All that is left now is to restore your saved data, and reinstall your programs.


After completing the above steps, my 2008 iMac came “back to life”.  It is faster than it has been for a long time, even faster than “before” the Yosemite install.  An additional benefit to this process is that I now have more hard drive space, – there were a lot of programs on my hard drive prior to Yosemite that I did not use, so I did not install them.

This process is not difficult, but it is time consuming, and well worth the effort.


Upgrade to OS X Yosemite.  Free on the Mac App Store.  |  Apple Support

Startup key combinations for Intel-based Macs | Apple Support

Use rsyncTo Backup Your Data On Mac OS X or Linux  |

Getting started with IMAP and POP3  |  Google Support

How to burn your own Lion install DVD….  | Life Hacker

How to Create A Bootable Install USB Drive…..  | WonderHowTo

OSX:  About OS X Recovery  |  Apple Support

OS X System Recovery:  Explored and Explained  |  Tuts – Computer Skills

By prometheus

Husband. Father. Grandfather. World class Geek.

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