Rebuilding A Mac From Scratch

I have a Mid–2012 MacBook Air. It’s a great machine, but lately I’ve been having problems. Nothing dire, but noticeably more frequent application and system freezes, apps not working the way they should, and just in general the Mac didn’t “feel” right. This machine is about two years old and has already been through a couple of OS upgrades. On top of that, I used Migration Assistant to bring over all my data from my previous Mac, as well as the Mac before that, and the Mac before that.

Apple has just made the process of upgrading operating systems and migrating data over to a new machine so easy, and generally painless, that I now forego my previous ritual of erase and start anew (or as I prefer to all it, “nuke and pave”) anytime there is a major OS upgrade or I purchase a new machine. I had a free day this weekend and given the problems I was having, thought this was as good a time as any to erase my Mac and re-start from scratch.

Prep Work

I didn’t want to bring over any unnecessary documents and files, so I took some time to go through the files and folders on my Mac and do some clean-up. I didn’t care much about cleaning up applications, plug-ins, or any system specific files because those would all be erased. Instead, I focused on my documents and data. I used PhotoSweeper to clean out duplicates in my iPhoto library, and I used tools like DaisyDisk and OmniDiskSweeper to find any files on my Mac that could be deleted. I also manually combed through my Documents folder and trashed or archived several folders and documents. (Did I really need that paper I wrote in college that was still lingering on my hard drive?)

You want to take inventory of all the applications you use and make sure you can put your hands on the installers, the registration information, and any special settings. The Mac App Store has simplified much of this process. When practical, I like to purchase simple Apps from the Mac App Store because it makes re-installing them a snap. For Apps where using the Mac App Store is not possible or impractical (due to lack of upgrade support, sandboxing restrictions, etc.) I store information about the applications, including the registration information and download links, in 1Password. For Applications that are difficult to re-download, I save their installer applications or create disc images of their install CDs or DVDs to my Drobo, inspired by David’s Magic Install Disk Screencast.

Another important step is to copy any important settings and files that wouldn’t be stored in your Documents folder. For example, Hazel rules, Keyboard Maestro Macros, AppleScripts, and application databases that aren’t synced via some kind of cloud service. Sometimes, you can export this information directly from the application for safe keeping and re-import it after you reload the App on your clean install. Other times, you’ll have to find where the App stores this information (usually somewhere in your ~/Library folder) and manually move it over. However, I discourage you from just copying and preserving your entire Library folder and bringing it over to your clean install. Remember, the purpose of this exercise is to get as clean a start as possible so you want to migrate over as little as possible and rebuild from scratch. You’ll probably miss a few things and this is why it’s a good idea to have a spare backup sitting on your shelf for a while - more on this in the next section.


When you decide to erase your computer you no longer have a backup. Until your files are completely restored, your backup becomes your primary data source. Which means, you better be confident in your backup method. I use a combination of off-site backup, local backup via Time Machine, as well as a local clone backup. For a project like this, the clone backup (an exact duplicate of my Mac’s hard drive which I create with SuperDuper! or Carbon Copy Cloner) is the most valuable.

You want to make sure that once your prep work is complete all your backups are up-to-date. Whenever I undertake a major project or change such as this, I usually make one additional backup of my system that I then pull out of rotation and sit on a shelf for at least a month, sometimes more, until I’m absolutely confident I have restored all my files and settings. Sometimes it can take you days, or possibly even weeks or longer, to realize you missed a critical file or setting. By then you may not be able to retrieve it from your normal backup methods as they may have all been overwritten with new data.

Download and Install

Once your prep work and backups are done, you’re ready to erase your Mac. The easiest way to do this is by booting from the recovery partition on your machine. Disconnect all unnecessary devices (leaving only a keyboard, mouse, Internet and power connected) and restart your Mac while holding down the ⌘ and R keys. Your Mac will start up to a simplified interface and you’ll see an option to run Disk Utility. For good measure, go head and run a repair of the primary disk. If there is any problem with the disk, you want to know now before you spend the next few hours installing and reloading your machine. Once the disk checks out clean, you can erase it.

At this point, all your data is gone and there’s no turning back. Macs haven’t shipped with installation CDs in years, so in order to truly start from scratch you’ll need to download a clean copy of the latest OS from the Internet. This is a large file so high speed Internet is a must. On my cable connection, it took me a little over an hour to download Mavericks. You’ll need to authenticate with your AppleID so Apple knows you have authorization to download the OS. Once the download is finished, the install will begin. It took about 20 minutes on my 2.0 GHz Core i7 with an SSD.

If you don’t have Internet access, or you have slow Internet access, you can create a bootable install drive as an optional installation method.

Initial Setup

Once the installation is complete, you’ll be walked through the process of setting up your new Mac including creating a user account. I recommend in order to avoid any permissions conflicts that you use the same username and short name as you did on your previous machine.

During the initial setup, you’ll be asked to provide your AppleID, which will setup iCloud syncing. With so much information now stored in iCloud this really eases a lot of the pain of setting up a new Mac form scratch. Within a few minutes my email, contacts, and calendars were already synced and data I had stored in iCloud from various applications, including apps like 1Password, BywordPagesand others were already on my Mac.

Since you installed your operating system direct from Apple, you should be fairly up-to-date, but I found a few small software updates were available so it’s a good idea to immediately run Software Update to make sure your system is current. You may need to manually run Software Update a few times throughout the setup process and as you install new Apps to make sure you are fully updated.

The first thing I did was head over to the Mac App Store and start the process of installing a few “mission critical” programs. First, 1Password as all of my software registration information was stored in there. Dropbox was the second application I installed to start downloading my synced stored files. I found that the Mac App Store also started the process of installing some of the iWork and iLife applications automatically.

Next, I plugged in my clone drive I made just before erasing my machine and started selectively restoring files including my Documents Folder, my iTunes and iPhoto libraries, and my Photos and Movies folder. Because these can be large files, connecting these drives by Thunderbolt or USB 3.0 will make a big difference.

While my files were restoring, I then headed back to the Mac App Store and started re-downloading Apps by going through my purchased history and selecting the Apps I knew I wanted re-installed. I also went through my software list in 1Password and started downloading and installing third party software to re-populate my Apps folder, making sure to only download those applications I actively used as the purpose of this exercise was to clean out the junk and that includes unused applications.

After about two hours of copying files over from my clone, downloading and installing apps, and tweaking settings, I was over 90% back to normal. It will take me several days of use and tweaking to get all my applications and settings back to the way I like them, but overall this was a huge improvement over the last time I performed a “nuke and pave” several years ago. Cloud storage, syncing services, and the Mac App Store have made the process of setting up a Mac from scratch much faster and easier. It’s now an afternoon project rather than a weekend affair.

A Few Hiccups

The first major problem I ran into was configuring Mavericks to accept my Exchange account which I use through Office 365 for work. I’ve never had any problem using Exchange with any recent version of OS X and had my accounts successfully setup on my previous system. For whatever reason, even with a clean install of the OS, the Internet Accounts System Preference pane threw errors when trying to add my Office 365 credentials, and all of Apple’s apps (Mail, Calendar and Contacts) unexpectedly quit when I tried to manually add Exchange accounts.

I called AppleCare and after jumping through a few hoops, they were baffled. I finally setup Exchange email using IMAP and interestingly, BusyCal took my Exchange login information and accessed my calendar just fine but this left me without access to my contacts. I was able to restore the account information by restoring information in my ~/Library/Mail, Address Book and Contacts folders from my clone backup. This leads me to believe there was some bug in OS X preventing the initial connection and validation, but once the credentials were supplied the connection was allowed.

I also found that I was missing a few application settings and information. Specifically, my AppleScripts and Hazel rules. These were easy enough to restore by going back to the ~/Library/Application Support and /Preferences folders on my clone drive and selectively restoring the proper settings. I’ll no doubt find a few more of these types of things over time, but again, that’s why I keep the backup on the shelf for a while.

Was It Worth It?

In a word, yes. But that doesn’t mean you should run out and do it.

Setting up a Mac from scratch is not an easy task. First, you have to set aside several hours for the preparation, installation, and setup. Even after you have your machine up and running, you’ll find for days, if not much longer, settings are out of place and things you forgot to configure. No doubt, it’s much easier to migrate data from a backup. But sometimes it’s good to get a fresh start.

I’ve been using my cleaned up system for a couple of days now and I can report things are running much more smoothly. I haven’t experienced any unexpected slowness, freezes, or crashes (other than the Exchange bug). Additionally, a few lingering problems with specific applications I was dealing with before have disappeared.

Perhaps the biggest benefit, I’m now running with much more free disk space than ever before. Before the migration process I kept about 40 - 50 GB free on my startup disk. Right now, I have 116 GB free. For a 256 GB SSD, that space recovery is huge. Some (but not much) of that savings is due to my pre-erase cleanup. But most of it comes from Applications I haven’t re-installed and all the bloat that had accumulated in my ~/Library folder over the years from several operating systems and computer migrations.

A “nuke and pave” can have its advantages. But that doesn’t mean it’s something that has to be done every time you upgrade your OS or buy a new Mac. It’s probably been 4–5 years since I last went through this practice and it was only recently I started to notice any kind of problems. With Apple releasing operating system upgrades more frequently, I’m not sure it makes sense to start a Mac from scratch every major OS update, unless you’re experiencing problems that haven’t been solved through traditional troubleshooting methods. But depending on how often you swap out computers, it may be something to consider.


This article first appeared in the June Issue of ScreencastsOnline Monthly Magazine. ScreenCastsOnline monthly magazine is packed with hints, tips, articles and links to streamable versions of ScreenCastsOnline tutorials and delivered monthly via Newsstand on the iPad. You can find out more at