Attention attention: The following are all the documents on apple’s official website. I just need to downgrade and gather them together for reference only. I think it is more reliable to complete the operation by myself.

How do I create a bootable macOS installer

You can use an external drive or spare volume as a boot disk to install the Mac operating system.

The following advanced steps are intended for system administrators and others familiar with the command line. A bootable installer is not required to upgrade or reinstall macOS, but can be useful if you want to install macOS on multiple computers and don’t want to download the installer every time.

 

Conditions that need to be met to create a bootable installer

  • USB flash drive or other spare volume (formatted as Mac OS extension format) with at least 14GB of available storage
  • Installers for macOS Monterey, Big Sur, Catalina, Mojave, High Sierra or El Capitan have been downloaded

 

Download the macOS

The installer for macOS Monterey, macOS Big Sur, macOS Catalina, macOS Mojave or macOS High Sierra will be downloaded to your Apps folder as an App, The name is Install macOS [version name]. If the installer opens after downloading, exit without continuing the installation. To obtain the correct installer, follow these instructions:

  • Please download it from a Mac that is compatible with the corresponding version of macOS.
  • Download it from a Mac running macOS Sierra 10.12.5 or later or OS X El Capitan 10.11.6.
  • Enterprise administrators: Please download from Apple instead of a locally hosted software update server.

The installer for ****OS X El Capitan is downloaded to your Downloads folder as a disk image named “Installmacosx.dmg”. To obtain an installer, follow the instructions below:

  • Download using Safari, then open the disk image on an OS X El Capitan compatible Mac.
  • Inside the disk image is an installer named “InstallMac OSx.pkg”. It installs an App called install OS X El Capitan in your Apps folder. You will create a bootable installer through this App rather than through a disk image or.pkg installer.

 

Use the createInstallMedia command in Terminal

  1. Connect the USB flash drive or other volume used to hold the bootable installer.
  2. Open Terminals in the Utilities folder in the Applications folder.
  3. Type or paste one of the following commands in Terminal. These commands assume that the installer is in your Applications folder and that “MyVolume” is the name of the USB flash drive or other volume that you are using. If not, place these commands inMyVolumeReplace it with the name of your schema.

Monterey: *

sudo /Applications/Install\ macOS\ Monterey.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
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Big Sur: *

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
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Catalina: *

sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
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Mojave: *

sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
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High Sierra: *

sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
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El Capitan.

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app
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  • If your Mac is running macOS Sierra or lower, use--applicationpathParameters and the installer path, similar to how this is done in a command for El Capitan.

After typing the command:

  1. Press the Return key to enter the command.
  2. When prompted, type your administrator password and press the Return key again. Terminal does not display any characters as you type your password.
  3. Type when promptedYTo confirm that you want to erase the volume, press the Return key. During the process of erasing a volume, Terminal displays progress.
  4. After the zong volume is erased, you may see an alert that prompts the Terminal to access files on the removable zong volume. Click OK to allow copying to continue.
  5. When Terminal indicates that the operation is complete, the corresponding volume will have the same name as the installer you downloaded, for example, Install macOS Monterey. You can now exit Terminal and pop up the volume.

 

Use a bootable installer

Determine if you are using a Mac with an Apple chip and follow these steps:

Apple chips

  1. Plug the bootable installer into a Mac that is connected to the Internet and compatible with the version of macOS you are installing.

    • The version of macOS that comes with the Mac is the earliest version available.
    • Bootable installers don’t download macOS from the Internet, but they do need an Internet connection to get mac-specific firmware and other information.

  2. Turn the Mac on and continue holding down the power button until you see the Boot options window, which displays bootable volumes.

  3. Select the volume that contains the bootable installer, and click Continue.

  4. Once the macOS installer is open, follow the instructions on the screen.

Intel processor

  1. Plug the bootable installer into a Mac that is connected to the Internet and compatible with the version of macOS you are installing.

    • The version of macOS that comes with the Mac is the earliest version available.
    • Bootable installers don’t download macOS from the Internet, but they do need an Internet connection to get mac-specific firmware and other information.

  2. Once the Mac is turned on or restarted, hold down the Option (Alt) ⌥ key.

  3. When you see a black screen showing bootable volumes, release the Option key.

  4. Select the volume that contains the bootable installer. Then press the up arrow or the Return key. If you are unable to boot from a bootable installer, make sure boot Security Utility is set to allow boot from external or removable media.

  5. Follow the prompts to choose your language.

  6. From the Utilities window, select Install macOS (or Install OS X), then click Continue and follow the on-screen instructions.

 

Learn more

To learn about the createInstallMedia command and the parameters that can be used with it, make sure the macOS installer is in your Applications folder, and then enter the appropriate path in Terminal:

/Applications/Install\ macOS\ Monterey.app/Contents/Resources/createinstallmedia
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/Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia
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/Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia
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/Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia
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/Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia
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/Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia
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Back up your Mac with the Time Machine

Learn how to create a backup of files on a Mac.

Use the Mac’s built-in backup feature, the Time Machine, to automatically back up your personal data, including apps, music, photos, emails and manuscripts. After backing up, you can restore files that were later deleted or inaccessible. Learn how to restore a Mac from a backup.

Create a Time Machine backup

  1. Connect an external storage device, such as a USB or gimbal drive. Learn more about the backup disks you can use with the Time Machine.
  2. “Time Machine” menu from the menu barTurn on the “Time Machine” preferences. Or go to the Apple menu  > System Preferences and click Time Machine.
  3. Click Select Backup Disks.

  4. Select a name for the disk, and then click Use Disk. The Time Machine will immediately start automatic periodic backups, requiring no further action.

 

If you want to start the backup manually, rather than waiting for the next automatic backup, please go to the “Time Machine” menu in the menu barSelect Immediate Backup.

Using this menu, you can also view the status of a backup or skip a backup in progress. For example, if a backup is in progress, this menu shows the progress of the backup completion. If a backup is not in progress, this menu displays the latest backup date and time.



Backup in progress



Latest backup

Learn more

  • The Time Machine automatically creates hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for all past months. If the backup disk is full, the earliest backup is deleted. The initial backup may take a long time, but you can continue to use the Mac while the backup takes place. The Time machine will only back up files that have changed since the last backup, so future backups will be faster.
  • To exclude items from the backup, turn on the Time Machine preferences, click Options, and then click the Add (+) button to add items to exclude. To stop excluding an item (such as an external hard drive), select the item and then click the Remove (-) button.
  • If you are backing up to multiple disks, hold down the Option key and choose Browse Additional backup disks from the Time Machine menu.
  • Learn about other ways to back up and restore files.

How do I get older macOS

If your Mac isn’t compatible with the latest version of macOS, you may be able to upgrade to an older version of macOS, such as macOS Big Sur, Catalina, Mojave or High Sierra.

To get the latest Mac features and keep Mac security, stability, compatibility, and performance up to date, make sure you keep your software up to date. Apple recommends that you always use the latest version of macOS that is compatible with your Mac.

Learn how to upgrade to macOS Monterey (the latest version of macOS).

Checking Compatibility

The version of macOS that comes with the Mac is the earliest version available. For example, if your Mac ships with macOS Big Sur, it can’t use macOS Catalina or earlier. If a macOS is incompatible with your device, the App Store or installer will let you know. If you try to install macOS earlier than the current version, the installer will prompt you that the version you want to install is too old to open on the current version of macOS.

  • MacOS Big Sur 11 Hardware requirements
  • MacOS Catalina 10.15 Hardware requirements
  • MacOS Mojave 10.14 hardware requirements
  • MacOS High Sierra 10.13 Hardware requirements
  • MacOS Sierra 10.12 hardware requirements
  • OS X El Capitan 10.11 Hardware requirements
  • OS X Yosemite 10.10 Hardware requirements

 

Make a backup

It’s a good idea to back up your Mac before installing any upgrades. The Time Machine makes backups easy, and there are other backup methods available.

 

Download macOS on a Mac using Safari

Safari will use the following link to find older installers in the App Store. When you download the installer from the App Store, it opens automatically.

  • MacOS Big Sur upgrades Catalina, Mojave, High Sierra, Sierra, El Capitan, Yosemite, Mavericks
  • MacOS Catalina upgrades Mojave, High Sierra, Sierra, El Capitan, Yosemite, Mavericks
  • MacOS Mojave can be upgraded to High Sierra, Sierra, El Capitan, Yosemite, Mavericks, Mountain Lion
  • MacOS High Sierra upgrades Sierra, El Capitan, Yosemite, Mavericks, Mountain Lion

Safari downloads the following older installers as a disk image named “installos.dmg” or “Installmacosx.dmg”. Open the downloaded disk image, and then open the.pkg installer within it. It will install an App called install [Version name]. Open the App from the Applications folder to begin installing the operating system.

  • MacOS Sierra can be upgraded to El Capitan, Yosemite, Mavericks, Mountain Lion, or Lion
  • OS X El Capitan can be upgraded to Yosemite, Mavericks, Mountain Lion, Lion, or Snow Leopard
  • OS X Yosemite can be upgraded to Mavericks, Mountain Lion, Lion, or Snow Leopard

How do I reinstall macOS

Reinstall the Mac operating system using macOS Recovery.

Boot with macOS Recovery

First make sure your Mac is connected to the Internet. Then determine if you are using a Mac with an Apple chip and follow the steps accordingly:

Apple chips

Turn the Mac on and continue to hold down the power button until you see the boot options window. Click on the gear icon marked “Options” and then click “Continue”.

Intel processor

Start the Mac and immediately press Command (⌘) -r until you see the Apple logo or other image.

  

If the system asks you to select a user whose password you know, select such a user, click Next, and enter the user’s administrator password.

Reinstall macOS

Reinstalling macOS does not remove data from the Mac. To begin the installation, select Reinstall macOS from the macOS Restore Utility window, then click Continue and follow the on-screen instructions.

During installation, follow the following guidelines:

  • If the installer asks you to unlock your disk, enter the password you used to log in to your Mac.
  • If the installer does not recognize your disk or indicates that it cannot be installed on your computer or volume, you may need to wipe the disk first.
  • If the installer gives you a choice to install on Macintosh HD or Macintosh HD-Data, select Macintosh HD.
  • Do not put the Mac to sleep or close the cover until the installation is complete. The Mac may reboot several times and display a progress bar, and the screen may remain blank for several minutes at a time.

After the installation is complete, the Mac may reboot and display the Settings Assistant. If you want to sell, discount, or give away a Mac, press Command-q to exit the assistant without completing the setup. Then click “Power off”. When the new owners start the Mac, they can use their own information to complete the setup.

Other macOS installation options

When you install macOS from the Recovery feature, you get the latest version of the most recently installed macOS, but there are some exceptions:

  • On Intel-based Macs, you can use shift-option-Command-r at boot time to get the Mac’s built-in macOS, or the version closest to it that is still available. Alternatively, you can use option-command-r at boot time to get the latest version of macOS compatible; In some cases, you can also get the Mac OS that comes with the Mac or the version closest to it that is still available.
  • If you’ve just replaced a Mac motherboard, you’ll probably only get the latest version of macOS that is compatible with the Mac.
  • If you’ve just wiped the entire boot disk, you’ll probably just get the Mac OS that came with it, or the closest version that’s still available.

If macOS is compatible with your Mac, you can also install macOS using the following methods:

  • Use the App Store to download and install the latest version of macOS or an earlier version of macOS.
  • Use a USB flash drive or another spare bundle to create a bootable installer.

Use the Disk Tool to erase the Intel-based Mac

How to erase (format) intel-based Mac’s built-in boot disk.

The following steps do not apply to Macs with Apple chips. If you use a Mac with an Apple chip, follow the steps for erasing a Mac with an Apple chip.

Before I erase the Mac

  1. If you want to restore your Mac to factory Settings (for example, to prepare for handing it over to a new owner), know what to do before you sell, give it away, or trade it in.
  2. If you’re using macOS Monterey on a Mac with Apple’S T2 security chip, follow the steps to erase all content and Settings instead of completing the steps below.
  3. Back up all the files you want to keep. Erasing your Mac permanently erases files from your computer.

Use disk Tool to erase the Mac

  1. Start from macOS Restore: Start the Mac and immediately press the Command (⌘) and R buttons until you see the Apple logo or other image.

  2. If you are asked to select a user whose password you know, do so and enter the administrator password for that user.

  3. From the Utility window, select Disk Tools, and click Continue.

  4. On the Disk Tools sidebar, select Macintosh HD. Can’t see “Macintosh HD”? \

  5. Click the “Erase” button in the toolbar and enter the details you want:

    • Name: Macintosh HD
    • Format:Use the APFS or Mac OS Extended (Logging) format as recommended by Disk Tools

  6. Click erase. But if you see the “Erase volume Group” button, click this button instead.

  7. If the system asks you to enter your Apple ID, do so. Forgot your Apple ID?

  8. When the erase operation is complete, select any other internal volumes in the sidebar, and then click the Delete Volume (-) button in the toolbar to delete the corresponding volume. In this step, ignore any built-in volumes named “Macintosh HD” or “Macintosh HD-Data,” as well as any volumes in the “External” and “Disk Image” sections of the sidebar.

  9. Exit Disk Tools to return to the Utilities window.

  10. If you want to reboot from the erased disk, select Reinstall macOS in the Utility window, then click Continue, and follow the on-screen instructions to reinstall macOS. \

If you do not see “Macintosh HD” in Disk Tools

Your built-in boot disk should be the first item listed in the Disk Tools sidebar. Unless you change the name, it’s called “Macintosh HD.” If you can’t see it there, select the Apple menu  > shutdown, then unplug all unnecessary devices from your Mac and try again.