Generally a reinstallation of your operating system is a last-resort option, but while recommended as such, there are times when problems warrant a reinstall. For instance, if your OS has been damaged by malware or a problematic third-party application, or if after updating you find a required program you use is not functioning properly, then you can perform a reinstallation to fix your OS, or roll back the version that works with your programs.
Granted the use of Time Machine and system cloning tools makes fully-restorable backups of your computer easy to create and use; however, sometimes reinstalling the OS can be quicker and keep your current settings as-is. This may be especially true if you have excluded folders from your regular backups, but wish to hold onto them when you restore OS X.
OS X Lion and Later
Starting with Lion, Apple has made OS X available for reinstallation online through the use of the OS X Recovery partition. Therefore, to reinstall OS X, you just need an active network connection, and then follow this procedure:
- Reboot your Mac
- Hold down the Command-R keys when you hear the boot chimes
- Release the keys when you see the Apple logo and spinning wheel
- Select your Language
- Select “Reinstall OS X” from the tools window
After doing this, follow the on-screen instructions to download and reinstall OS X. This process should only replace system files on your Mac, leaving user accounts, settings, and installed applications intact. After restarting, check the version of OS X that was installed, which can be seen in the “About This Mac” panel in the Apple menu.
If you simply need the latest version of OS X, then you can use Apple’s software update to get the most recent versions of all Apple-provided software. However, if you would like an intermediary version, then you can download and install the Combo updater for the desired version from Apple’s Support Downloads Web page(). For example, for OS X 10.9.2, search the page for “OS X 10.9.2 Combo” and then download the disk image, open it, and run the installation package contained in it. This will update your system to 10.9.2, even when OS X 10.9.3 or later are the only options available for download through Software Update.
Before OS X Lion
If you are attempting to reinstall a version of OS X before Lion, then you will need to do so from the installation DVD (either retail, or gray restore DVD that came with your Mac). To do this, follow these steps:
- Insert your installation DVD
- Reboot your Mac
- Hold down the “C” key to boot to the optical drive
- Follow the On-screen instructions to reinstall.
What does reinstalling do and what to expect?
You may be concerned about the idea of reinstalling an operating system, since classically this has meant wiping the drive and then needing to restore all of your settings, documents, programs, and other customizations you have made to it; however, with OS X this type of frustration has been minimized. When you reinstall OS X, the installer will only replace system files, leaving your account, settings, data, and programs intact. As a result, in most cases a reinstall will result in a seamless experience that simply rolls you back to a prior version of OS X.
Keep in mind that sometimes a program you have already installed or perhaps recently updated may require a specific version (or later) of OS X to run, and by reinstalling sometimes the program may run into problems if launched immediately. Therefore, be sure to update your system to the desired version as soon as possible.
As for third-party programs, in most cases they are fairly self-contained so a reinstall will not affect them; however, there may be some instances where program elements more spread through the system, and could be adversely affected by the reinstall. For these situations, it is best to simply keep them in mind and be on the lookout as you use your system. First be sure to update your system software after reinstalling, and then peruse your programs and try them out. If any show problems, then consider reinstalling them.