De Kleine Leeuwarder Napoleon

How to Reinstall OS X on a Mac


Before getting started, you’ll want to be sure you have a fast and stable internet connection available for the Mac, this is because the installer files for OS X download from Apple. Trying to reinstall OS X through a flakey or slow internet connection is not recommended, unless you were to use a bootable install drive or something similar where downloading reinstallation components is not necessary. You’ll also want to set aside at least an hour or two to complete this process, the exact time it takes depends on the speed of the internet connection in use, and the speed of the Mac.

Reinstalling OS X System Software on a Mac with Recovery Mode

It’s a good idea to back up the Mac with Time Machine before beginning this process. Even though this method aims to only reinstall OS X system software on the Mac, things could still go wrong and it’s always better to lean on the side of caution and make file backups beforehand.

1 Reboot the Mac and hold down the Command+R keys until you see the loading screen to signify you are entering into System Recovery

2 When you see the OS X “Utilities” menu, you should connect the Mac to the internet however you normally do – this is required* to download the OS X installer app:

      3 Once the Mac is connected to the internet, from the OS X Utilities screen choose “Reinstall OS X”

      Pasted Graphic


      4 Select the target hard drive to re-install OS X onto (typically “Macintosh HD” but varies per user) – if the Mac has a FileVault password set choose to “Unlock” and enter the FileVault encryption password before proceeding further

      Pasted Graphic 1Pasted Graphic 2


      5 The Recovery drive will now download “additional components” necessary to reinstall OS X on the target volume, let this process complete and the Mac will automatically reboot itself when done.

      6 You may encounter a user login screen upon first reboot, login to the admin user account as usual, and the Mac will again reboot itself to start the reinstallation process of Mac OS X system software

      7 At the black screen with an Apple logo, you’ll see a progress bar indicating how much time is left to complete the reinstallation of Mac OS X, this is typically somewhere in the realm of an hour, just let the Mac sit and finish

      Pasted Graphic 3

      When reinstallation completes, the Mac will reboot itself again as normal, and you’ll be presented again with the typical login screen associated with OS X – log in to your user account as usual and everything should be in order, complete with a new install of OS X system software on the computer.

      As long as you didn’t erase the drive or delete any user accounts yourself, all user accounts, installed applications, and user data will be preserved, and only Mac OS X system software and system files will have been reinstalled without touching anything else on the Mac. If desired, you can use the
      Apple menu > About This Mac screen to verify the version of OS X that has been reinstalled

      • If you get an error message about being unable to reinstall OS X because the Mac isn’t connected to the internet, you need to join a wi-fi network or connect via ethernet. The installer must download from Apple for this to work.

      This works to reinstall OS X exactly as described, I had to run through this process recently when I encountered probably the worst and most bizarre bugs I’ve ever seen in OS X, where “Macintosh HD” became stuck in the Trash can and actually started deleting system level files when emptied, which as you can imagine leads to all sorts of problems with the operating system missing critical components. While it’s unlikely you’ll ever encounter such a bug yourself, it is possible for users to mess up their system folders if they have disabled SIP or are using root, if the startup Mac OS volume has been erased or misplaced, if a prohibitory symbol is encountered at startup (sometimes a folder with an X through it, or a folder with a blinking question mark), or if the OS X installation is erroneous or royally messed up.

      Remember, this method is not the same as a clean install, and it only reinstalls the version of OS X that is currently running on the Mac (shown here with El Capitan), whereas Internet Recovery will reinstall the version of OS X that shipped with the Mac (in this case it would have been Yosemite) instead. Obviously the versions of OS X will vary depending on what came with the Mac, and what the Mac is currently running.


      bron
      OSX Daily