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How To (Re)install macOS

Article ID = 35
Article Title = How To (Re)install macOS
Article Author(s) = Graham Needham (BH)
Article Created On = 13th July 2011
Article Last Updated = 25th February 2015
Article URL = https://www.macstrategy.com/article.php?35

Article Brief Description:
Instructions for (re)installing macOS specifically the "Archive and Install" or "Erase and Install" methods.

How To (Re)install Mac OS X

Some important points to note before proceeding:

Explanation of Different Install Methods:

NOTE A "clean install" is ambiguous. It can mean either an "Erase and Install" or an "Archive and Install". Both methods install Mac OS X cleanly but one erases everything on your boot disk first.
  • Erase and Install = (Automatically) erases the hard disk first, then installs Mac OS X - this method deletes all your personal data and applications!
  • Install Mac OS X for the first time = This is basically the same as the "Erase and Install" method but where you manually erase the hard disk first or you are installing to an empty hard disk.
  • Archive and Install = Available in Mac OS X 10.2 and later (except with "Upgrade" discs), an Archive and Install installation automatically moves existing system files to a folder named Previous System, then installs Mac OS X again. You cannot start up your computer using a Previous System folder, nor can you "re-bless" the Previous System folder. You can choose to preserve your user and network settings before installing. This option automatically moves existing users, Home directories, and network settings. This also skips the Setup Assistant after installation. (see this Apple article.)
  • Restore system = This option is referred to when you are using discs that originally came with your computer (see this Apple article). Using "restore" discs usually gives you similar options to the above three types but with the addition of installing extras like iLife applications at the same time.
  • Upgrade Install = This option is usually available when you are installing a newer version of Mac OS X on a disk that has an older version on it or you have an "Upgrade" disc.

Instructions For Installing Mac OS X

We recommend that you only use the Erase and Install (Install Mac OS X for the first time) or Archive and Install methods. Use the Erase and Install (Install Mac OS X for the first time) method when you would like to start from scratch (but this will involve reinstalling all your personal applications and data afterwards). Use the Archive and Install method when you are troubleshooting problems with your system and need to "reinstall the operating system".

Install Method Instructions In This Article:

Instructions for the Archive and Install method (Mac OS X 10.2, 10.3, 10.4, 10.5)
NOTE: Make sure you have enough free space on your hard disk before proceeding.
  1. Start up from the Mac OS X Install volume
    2. NOTE: Usually, you can start from an install disc by putting it in your computer, restarting, and holding down the C key or you may be able to hold down Option and choose the install disc from the Startup Manager.
  2. Select your language. Click the forward arrow button.
  3. The Welcome to the Mac OS X Installer window appears. Click Continue.
  4. The Important Information window appears. After reading or printing the information, click Continue.
  5. The Software License Agreement window appears. After reading or printing the information, click Continue.
  6. An agreement sheet appears. If you agree with the license agreement, click Agree.
  7. The Select a Destination window appears. Click the volume that you wish to install to.
  8. Click Options. The installation options sheet appears.
  9. Select "Archive and Install".
  10. You should also select/tick "Preserve Users and Network Settings".
  11. Click OK.
  12. Check the volume your are installing to is the correct one.
  13. Click Continue to begin the installation.
  14. When OS X has installed and the computer has restarted you should now install the required Mac OS X Combo update that you need
  15. Once the required combo update is installed keep going to Apple menu > Software Update to install all other required updates.
    16. NOTE: If you are reinstalling your system to avoid a Mac OS X update bug remember to use the Combo update for the version before and then when running Software Update to untick the version of Mac OS X that you don't want.
  16. When you are happy everything is installed and running okay and you have rescued anything you need from the "Previous System" folder you can delete the "Previous System" folder.
Instructions for the Archive and Install method (Mac OS X 10.6)
NOTE: Make sure you have enough free space on your hard disk before proceeding.
NOTE: Mac OS X 10.6 basically does an Archive and Install as the default installation method (but it no longer leaves a "Previous System" folder behind).
  1. Start up from the Mac OS X Install volume
    2. NOTE: Usually, you can start from an install disc by putting it in your computer, restarting, and holding down the C key or you may be able to hold down Option and choose the install disc from the Startup Manager.
  2. Select your language. Click the forward arrow button.
  3. The Welcome to the Mac OS X Installer window appears. Click Continue.
  4. The Important Information window appears. After reading or printing the information, click Continue.
  5. The Software License Agreement window appears. After reading or printing the information, click Continue.
  6. An agreement sheet appears. If you agree with the license agreement, click Agree.
  7. The Select a Destination window appears. Click the volume that you wish to install to.
  8. Click Continue to begin the installation.
  9. When OS X has installed and the computer has restarted you should now install the required Mac OS X Combo update that you need
  10. Once the required combo update is installed keep going to Apple menu > Software Update to install all other required updates.
    11. NOTE: If you are reinstalling your system to avoid a Mac OS X update bug remember to use the Combo update for the version before and then when running Software Update to untick the version of Mac OS X that you don't want.
Instructions for the Archive and Install method (OS X 10.7 or later) - using one of the following
NOTE: Make sure you have enough free space on your hard disk before proceeding.
NOTE: OS X 10.7 Lion or later basically does an Archive and Install as the default installation method (but it no longer creates a "Previous System" folder).
NOTE: If you install Lion using the official Apple USB thumb drive, you will not be able to reinstall Lion using the Lion Recovery mode. You will need to use the official Apple USB thumb drive to reinstall Lion.
  1. Start up from the Mac OS X Install volume
    2. NOTE: Usually, you can start from an install disc by putting it in your computer, restarting, and holding down the C key or you may be able to hold down Option and choose the install disc from the Startup Manager.
  2. The Mac OS X Utilities window reappears.
  3. Select "Reinstall Mac OS X" and click Continue.
  4. The Install Mac OS X window appears. Click Continue.
  5. The Software License Agreement window appears. After reading or printing the information, click Agree.
  6. An agreement sheet appears. If you agree with the license agreement, click Agree.
  7. The Select the disk where you want to install Mac OS X window appears. Click the volume that you wish to install to.
  8. Check the volume you are installing to is the correct one.
  9. Click Install to begin the installation.
  10. When OS X has installed and the computer has restarted you should now install the required Mac OS X Combo update that you need
  11. Once the required combo update is installed keep going to Apple menu > App Store… > Updates to install all other required updates.
    12. NOTE: If you are reinstalling your system to avoid a Mac OS X update bug remember to use the Combo update for the version before and then when running Software Update to untick the version of Mac OS X that you don't want.
Instructions for the Archive and Install method (OS X 10.7 or later) - using an OS X Install installer application from the Mac App Store
NOTE: Make sure you have enough free space on your hard disk before proceeding.
NOTE: OS X 10.7 Lion or later basically does an Archive and Install as the default installation method (but it no longer creates a "Previous System" folder).
  1. Copy the OS X Install installer application to your hard disk/Applications folder
  2. Double click the OS X Install installer application.
  3. The Install Mac OS X window appears. Click Continue.
  4. The Software License Agreement window appears. After reading or printing the information, click Agree.
  5. An agreement sheet appears. If you agree with the license agreement, click Agree.
  6. The Select the disk where you want to install Mac OS X window appears. Click the volume that you wish to install to.
  7. Check the volume you are installing to is the correct one.
  8. Click Install to begin the installation.
  9. When OS X has installed and the computer has restarted you should now install the required Mac OS X Combo update that you need
  10. Once the required combo update is installed keep going to Apple menu > App Store… > Updates to install all other required updates.
    11. NOTE: If you are reinstalling your system to avoid a Mac OS X update bug remember to use the Combo update for the version before and then when running Software Update to untick the version of Mac OS X that you don't want.
Instructions for the Erase and Install method or installing Mac OS X for the first time
(Mac OS X 10.2, 10.3, 10.4, 10.5, 10.6)
NOTE: Make sure you have a full, current backup or clone of your system/setup before proceeding.
NOTE: Mac OS X 10.6 does not have an Erase and Install option so you should follow the manual erase of your hard disk instructions below.
  1. Start up from the Mac OS X Install volume
    2. NOTE: Usually, you can start from an install disc by putting it in your computer, restarting, and holding down the C key or you may be able to hold down Option and choose the install disc from the Startup Manager.
  2. Select your language. Click the forward arrow button.
  3. The Welcome to the Mac OS X Installer window appears.
  4. The Important Information window appears.
  5. If you are going to manually erase your hard disk and then Install Mac OS X for the first time:
    1. Go to the Utilities menu and select "Disk Utility".
    2. Format your hard disk.
    3. Quit Disk Utility.
    4. The Important Information window reappears.
  6. After reading or printing the Important Information, click Continue.
  7. The Software License Agreement window appears. After reading or printing the information, click Continue.
  8. An agreement sheet appears. If you agree with the license agreement, click Agree.
  9. The Select a Destination window appears. Click the volume that you wish to install to.
  10. If you have not manually erased your hard disk:
    1. Click Options. The installation options sheet appears.
    2. Select "Erase and Install".
    3. Select the format for the disk you are automatically erasing (usually "Mac OS Extended" for Mac OS X 10.2 / "Mac OS Extended (Journaled)" for Mac OS X 10.3 and later).
    4. Click OK.
  11. Check the volume you are installing to is the correct one.
  12. Click Continue to begin the installation.
  13. When OS X has installed and the computer has restarted you should now install the required Mac OS X Combo update that you need
  14. Once the required combo update is installed keep going to Apple menu > Software Update to install all other required updates.
    15. NOTE: If you are reinstalling your system to avoid a Mac OS X update bug remember to use the Combo update for the version before and then when running Software Update to untick the version of Mac OS X that you don't want.
Instructions for the Erase and Install method (OS X 10.7 or later) - using
NOTE: Make sure you have a full, current backup or clone of your system/setup before proceeding.
  1. Start up from the OS X Install volume
    2. NOTE: Usually, you can start from an install disc by putting it in your computer, restarting, and holding down the C key or you may be able to hold down Option and choose the install disc from the Startup Manager.
  2. The OS X Utilities window appears.
  3. Select "Disk Utility" and click Continue.
  4. Format your hard disk.
  5. Quit Disk Utility.
  6. The OS X Utilities window reappears.
  7. Select "Reinstall OS X" and click Continue.
  8. The Install OS X window appears. Click Continue.
  9. The Software License Agreement window appears. After reading or printing the information, click Agree.
  10. An agreement sheet appears. If you agree with the license agreement, click Agree.
  11. The Select the disk where you want to install OS X window appears. Click the volume that you wish to install to.
  12. Check the volume you are installing to is the correct one.
  13. Click Install to begin the installation.
  14. If you installed OS X via the internet you will have automatically installed the latest version of OS X. If you installed it from a backup of the OS X installer you may need to install the latest OS X Combo update:
  15. Once OS X (and any combo update) is installed keep going to Apple menu > App Store… > Updates to install all other required updates.
    16. NOTE: If you are reinstalling your system to avoid a OS X update bug remember to use the Combo update for the version before and then when running Software Update to untick the version of OS X that you don't want.
    NOTE: If your computer came with OS X 10.7 Lion or later your iLife applications have to be downloaded separately via the Mac App Store afterwards.

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