The idea behind a macOS Clean Install

Usb

Make sure to create a macOS Catalina USB installer before you update your MacBook and start exploring Catalina features. While you don’t need a bootable installer to install macOS Catalina, it’s a good option for people with a limited or sporadic internet connection, multiple Macs, or who want a backup installer for emergencies. Step 1: Download macOS Sierra from the Mac App Store. To create a USB installer for macOS Sierra, you first need to download the installation application from the Mac App Store. Using a compatible Mac, simply launch the App Store, find Sierra from the homepage sidebar, and download the installer. Once it has completed the download, the Sierra.

Install

When you install a new major version of OS X, or after some time has passed, it is a good idea to do a clean install (that is, to erase the disk you are installing OS X onto as part of the installation process).

That will make your Mac run blazingly fast for a few months or more, and many people report that it fixes longstanding problems they’ve had too.

It used to be common practice to occasionally run a clean install, and then manually migrate all the files and settings over in order to get a completely fresh start. However, it has been shown in recent times that in the vast majority of cases if you simply run a clean install, then duplicate your old home folder to your new disk, you will get all of the same advantages as a clean install followed by manual migration, with a small fraction of the effort.

Mac Clean Install Procedure

Here is the clean install procedure which can be performed at least every time a new version of macOS is released:

  1. Download the macOS installer from the App Store. You can download macOS Big Sur by clicking here.
  2. Backup all the data to an external disk with a clone. Two options are to use Duplicate (a free utility which can copy and paste an entire bootable volume), or Mac Backup Guru (a paid, fully featured backup utility with unique incremental backups capability) for that.
  3. Create a bootable USB Installer with Install Disk Creator and boot from it. Erase the startup disk and install macOS onto it. Boot up from this newly created startup disk.
  4. Note: The Finder’s built-in “Copy” and “Paste” will not work for the following.
    Go to the backup disk and use Duplicate (free) or Mac Backup Guru to right-click and select Copy on the home folder (eg: External Backup/Users/Bob) and then Paste on the Macintosh HD/Users folder on the startup disk. This migrates all of your personal data and settings to your new home folder.
    Then migrate the applications by selecting Copy on the External Backup/Applications folder on the backup disk then Paste on the startup disk (eg: Macintosh HD). This will copy all of the applications which are present on the backup disk but not present on the startup disk to your new Applications folder, and automatically skip any applications which are already on the startup disk.

At this point, after a reboot and some minor adjustments (the Dock may not have your previous configuration for example, if you did this while logged into the same user account as you just updated), your new OS should be indistinguishable from your previous one, while being faster and smaller due to reduced clutter.

These advanced steps are primarily for system administrators and others who are familiar with the command line. You don't need a bootable installer to upgrade macOS or reinstall macOS, but it can be useful when you want to install on multiple computers without downloading the installer each time.

What you need to create a bootable installer

  • A USB flash drive or other secondary volume formatted as Mac OS Extended, with at least 14GB of available storage
  • A downloaded installer for macOS Big Sur, Catalina, Mojave, High Sierra, or El Capitan

Download macOS

  • Download: macOS Big Sur, macOS Catalina, macOS Mojave, or macOS High Sierra
    These download to your Applications folder as an app named Install macOS [version name]. If the installer opens after downloading, quit it without continuing installation. To get the correct installer, download from a Mac that is using macOS Sierra 10.12.5 or later, or El Capitan 10.11.6. Enterprise administrators, please download from Apple, not a locally hosted software-update server.
  • Download: OS X El Capitan
    This downloads as a disk image named InstallMacOSX.dmg. On a Mac that is compatible with El Capitan, open the disk image and run the installer within, named InstallMacOSX.pkg. It installs an app named Install OS X El Capitan into your Applications folder. You will create the bootable installer from this app, not from the disk image or .pkg installer.
Usb

Use the 'createinstallmedia' command in Terminal

  1. Connect the USB flash drive or other volume that you're using for the bootable installer.
  2. Open Terminal, which is in the Utilities folder of your Applications folder.
  3. Type or paste one of the following commands in Terminal. These assume that the installer is in your Applications folder, and MyVolume is the name of the USB flash drive or other volume you're using. If it has a different name, replace MyVolume in these commands with the name of your volume.

Big Sur:*

Catalina:*

Mojave:*

High Sierra:*

El Capitan:

* If your Mac is using macOS Sierra or earlier, include the --applicationpath argument and installer path, similar to the way this is done in the command for El Capitan.


After typing the command:

  1. Press Return to enter the command.
  2. When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.
  3. When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the volume is erased.
  4. After the volume is erased, you may see an alert that Terminal would like to access files on a removable volume. Click OK to allow the copy to proceed.
  5. When Terminal says that it's done, the volume will have the same name as the installer you downloaded, such as Install macOS Big Sur. You can now quit Terminal and eject the volume.

Use the bootable installer

Create Mac Install Usb

Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:

Apple silicon

  1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
  2. Turn on your Mac and continue to hold the power button until you see the startup options window, which shows your bootable volumes.
  3. Select the volume containing the bootable installer, then click Continue.
  4. When the macOS installer opens, follow the onscreen instructions.

Intel processor

  1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
  2. Press and hold the Option (Alt) ⌥ key immediately after turning on or restarting your Mac.
  3. Release the Option key when you see a dark screen showing your bootable volumes.
  4. Select the volume containing the bootable installer. Then click the up arrow or press Return.
    If you can't start up from the bootable installer, make sure that the External Boot setting in Startup Security Utility is set to allow booting from external media.
  5. Choose your language, if prompted.
  6. Select Install macOS (or Install OS X) from the Utilities window, then click Continue and follow the onscreen instructions.

Create Mac Os Install Usb

Learn more

Create Mac Install Usb On Linux

A bootable installer doesn't download macOS from the internet, but it does require an internet connection to get firmware and other information specific to the Mac model.

Create A Mac Install Usb From Windows

For information about the createinstallmedia command and the arguments you can use with it, make sure that the macOS installer is in your Applications folder, then enter the appropriate path in Terminal: