My MacBook Air used to be rock solid, but it has grown increasingly unstable over the past year. For example, this afternoon I can't switch to my other user account. I select the account from the fast user switching menu and nothing happens.

Part of me wants to just start over, reinstall and reconfigure OS X and all of my applications from scratch. It would probably solve a lot of problems. But I have so much work invested in my current configuration. It would take days or weeks to fully rebuild.

I'm thinking the next best option would be to wipe the drive and restore my latest Time Machine backup. I know that Time Machine doesn't back up everything -- caches, log files, etc. -- so maybe restoring from backup would have a "rejuvenating" effect. Or it could just be a complete waste of time.

In general, is reformatting and restoring from Time Machine a good way to get a Mac running like new? Or is it merely "worth a shot"?

3 Answers 3


I like MK's answer above. Look at those things first.

Then - consider this... I experienced something similar to what you are describing. I tried the erase, format and restore from Time Machine... it didn't really help. Then someone suggested starting up with the option key held down and reinstall the operating system. (this 'reinstalls' the OS while keeping all of your files!)

If you are running Mountain Lion or later, you can follow Apple's instructions here: http://support.apple.com/kb/PH10763?viewlocale=en_US

This solution worked much better for me.


There could be various causes for a Mac that runs slow during certain times:

  • too many applications running on the system (launched at login or explicitly by the user)
  • inadequate RAM
  • inadequate free space on the drive
  • file permission issues
  • corrupted files or configuration
  • updated OS and applications that need faster hardware, and so on

For all these cases, reformatting and restoring from Time Machine will not help.

If you'd like to clear caches and logs and repair permissions, there are far quicker and easier ways to do it than a time consuming reformat and restore from Time Machine. Make sure you have a backup and then try some of these utilities (you can also search for "OS X cleanup" to find other utilities):

If these do not help:

  • if you're running OS X Mavericks, check the Memory Pressure information in Activity Monitor - this will tell you if RAM is inadequate for the applications you're running
  • try trimming down the number of applications that are running. Start with items launched at login (go to System Preferences > Users & Groups and then to the Login Items tab)
  • free up disk space (if it's quite low)
  • using Activity Monitor, check which applications use a lot of CPU and either remove them or reinstall them afresh (trash the application with a proper uninstall utility like AppCleaner so that its preferences and other files are also deleted and then reinstall it)
  • as a last resort, you may have to do a fresh install of the OS, followed by a fresh install of your applications, followed by a restore of only your data from the Time Machine backup (do not restore the entire applications folder or the home folders since that would bring back corrupt preference files, if any)
  • 2
    My Mac isn't slow, actually, it's just a lot buggier than it used to be. It sometimes fails to wake from sleep, or it randomly rearranges my windows, or it won't send audio to my Apple TV.... It's got plenty of free memory and CPU cycles, though.
    – Metaphile
    Nov 12, 2013 at 5:39
  • It may still be related to corrupt files or permission issues. You could try a cleanup using the tools mentioned above and see if it makes things better.
    – M K
    Nov 12, 2013 at 11:02
  • 1
    I would try all of the above suggestions. Whatever you do don't install MacKeeper : discussions.apple.com/docs/DOC-3036
    – Deesbek
    Nov 12, 2013 at 14:22
  • 1
    Don't forget to repair permissions and volume of your boot volume while booted from recovery HD or an external boot volume. That should be the first step.
    – TooAToB
    Nov 12, 2013 at 15:26

If you are looking for a "rejuvenating" effect, depending of what version of Mac OS X you are running I would upgrade to Mountain Lion (OS X 10.8) or Maverics (OS X 10.9).

It is more likely to stabilise your system and is easier than doing a full rebuild.

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