Re-Installing Lion (Clean Install)

“Does my computer work again?”
“No, but if it did, it would be much faster.”
Office worker and tech support in a Dilbert comic (from memory and I read it a long time ago)

After installing Mac OS Lion over my existing Snow Leopard installation (I needed iCloud as MobileMe ceased working), my computer got very slow — and buggy. So it was time for a re-install, a clean one. Deleting all the data on the harddisk and re-installing the OS. It fixed the speed problem — my OS is now snappy again, much better than the prior installation. However, deleting all your data can have serious consequences, so if you want to do the same, here are a few things I noticed/did (absolutely no warranty):

Prior to the Clean Install

  • Backups, Backups, Backups. Using TimeMachine does not cut it. Once you delete the data on your notebook, you essentially loose one backup and all your data, all your work hinges on the working of a single harddisk drive. Never put all your eggs in one basket. I did multiple backups (I am paranoid — and work digitally) and keep them in different locations.
  • Make one final time machine backup on a drive you can do without for a while. What ever happens after the reinstall — if you miss something, some settings, some information, you can go back to this backup and get the data. I haven’t touched my old TimeMachine disk after the reinstall and will not do so for at least a month. This gives me time enough to recover what I have forgotten to secure.
  • Spring Cleaning. As you go through your files use the opportunity to discard what you no longer need. Most of the movies I had on my Mac ended up on two(!) dedicated harddisks. I’ve seen them and if I want to see them again, I can do so, but they do not need to take up space on my main computer.
  • Create manual backups by copying the data on different drives. DEVONthink worked really well — most of my data is in different DEVONthink databases, making backup easy (and moving the data back).
  • Make a list of the Apps you usually use. It is strange how quickly you miss an App when you download the software again.
  • Get all the software and the license codes together. Once you delete your harddisk drive, all software is gone and if you do not have the installation files or the license number, you cannot work. I checked whether I have the serial numbers for all my apps and went through them one by one — and still missed one (OmniFocus, see below).
  • Look in the non-obvious places for backups.Among others, I did manually backup:
    • my eMail directory (Library/Mail) — BTW, if you do not see your Library folder, go to the finder, the menu on top of the screen (“Go”), then “Go to Folder” and enter: /Users/YOURUSERNAME/Library
    • my AddressBook (Library/AddressBook)
    • Applications I might not find again (turned out to be unnecessary, I could download and install all apps I used)
    • Background images, etc.  I have all material to customize the look and feel of the OS in one folder and made sure I had it saved.
  • I did miss a few things, among others:
    • I did not copy the backup files of my iPhone/iPad — made synching the devices difficult with the new installation (see below — and see this guide prior to doing the re-install!!!!)
    • I did forget to export and secure my Firefox bookmarks
    • I did not have all Dashboard-Widgets as installation files — I no longer have the calendar widget I used
    • I did not think of the settings of FTP servers and the like stored in my FTP program

Doing the Clean Install

Note: If you are not comfortable working with computers, get help. Otherwise you might loose data! Again: No Warranty.

  1. I used this guide to create an installation on an USB stick which worked fine (note that you have to format the USB stick with a GUID partition type, also explained in the guide).
  2. Rebooting the Mac and pressing the Option key allowed me to start from the USB stick.
  3. This is the part where data gets lost — as a new install simply installs over your existing copy, I opened the Disk Utility to erase all data from my harddisk. After this step, your data is gone.
  4. Then install the OS.

After the Clean Install

  • Secure your Mac. For me this means going through the security options in the System Preferences, setting up the Firewall and going on stealth mode, ah, and pairing my remote.
  • Do a software update via the System Preferences.Unfortunately, iTunes made some problems (update did not work), so I downloaded the software from the website itself and manually reinstalled it.
  • Copy your data back. Personally, I did not use the TimeMachine backup but copied all data from a manual backup. Again, DEVONthink databases worked fine.
  • Customize your computer. A great time to change your workflow. BTW, if you are used to spaces from Snow Leopard, one stupid feature is that spaces rearrange themselves by default. Matt Gemmell has written a good description of how to use spaces and in this description of the first five things Code Fink does when he sets up Lion is a description of how to stop this stupid feature (and other great tips).
  • Get the Apps back. App Store makes this easy and you should use the App store if you have bought the App there. I downloaded OmniFocus from the website, but had originally bought it in the App store. Thus, I had no License number and noticed only recently that I had only a few days of use left. Unfortunately the App store showed me that it was already installed, making me believe I had installed it from the App store. The very helpful customer service gave me the hint to delete my copy in the Applications directory and download it again from the App Store. Worked like a charm.
  • Update the Apps. If you install them from DVDs or local copies, you might not have the current version.
  • Set up your devices for Sync. As I did not read this guide here, I used another hint I found online by first right-clicking on the device in iTunes and transferring my purchases (takes a while), and then right-clicking again and choosing backup (takes a while). Afterwards I selected sync and allowed iTunes to erase my data on the device. Luckily it turned out well — I had to rearrange my apps on the device, but all data was still available (I had them in the cloud anyway). But it could have gone wrong and I am not sure why it worked. So stick to the guide.

Other Aspects

All in all it worked surprisingly well — took me about a day (with time to do something else during the installation phases). Still, at times I have to stop and look something up — it is impressive how some little details that you do not remember anymore can make a difference when working.


  1. Hey Daniel, isn’t it the best idea to just make a copy of the entire harddisk? You could use something like CarbonCopy Cloner ( and in this way you will not have the risk of forgetting any data?
    Thanks for the interesting post, Max

  2. Hoi Max,

    the problem with copying your entire harddisk is that you would copy the OS too, and in this case, I think there were some problems with the OS (installing Lion over Snow Leopard). But keeping a complete backup somewhere in case you forget something, sure, that’s a good idea. Who knows whether there is some font or some data you have missed and will miss terribly after the reinstall.

    All the best


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