Reinstall Macos Catalina From Big Sur

15-09-2021 by

Summary: This page is about how to reinstall macOS in macOS Recovery mode. Based on if you want to keep the original data on the startup disk, you can either choose to clean reinstall macOS or to reinstall macOS without data loss.

Reinstalling macOS gives your Mac a fresh start especially when you are frequently bothered by some issues, such as Mac not turning on, Mac hanging on the beach ball, apps frozen on your Mac, slow performance, or pink screen on Mac. Most of the time, such issue results from some system-level problems, while reinstalling macOS can easily save your life.

• How to reinstall macOS on an M1 Mac?

How to reinstall macOS from macOS Recovery mode?

Big Sur is a big mess and a big fail! My sister downloaded it and her late 2015 iMac became useless. I tried to reinstall it and it hung up at the dreaded 'Less than one minute remaining' Now I have to do a clean erase and load Catalina. Reminds me of all the bad OS from Microsoft in the early days. 'macOS Big Sur' could not be verified.: I have tried twice to update from Catalina 10.15.7 to Big Sur and every time I get this message. Why does the update not work?.I have tried to install as per your feedback in safe mode, but it goes back to the fault message.” ———-Reinstall it All Anew.

When you need to reinstall macOS on your Mac, macOS Recovery mode makes this process easy and quick. By the way, if you want to learn more about macOS Recovery mode, you can watch this video.

To reinstall macOS in macOS Recovery mode:

Step 1: Make sure your Mac is connected to a stable Internet within all the following steps.

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Step 2: Identify it's an Intel or M1 Mac, and immediately do one of the followings.

  • Press and hold Command + Option + R.This allows you to reinstall the latest version of macOS that is compatible with your Mac computer from the internet.
  • Press and hold Shift + Command + Option + R. This option allows you to reinstall the macOS that came with your Mac, or the closest version still available.
  • Press and hold Command + R. This allows you to reinstall the version of macOS stored on your built-in recovery disk, including any updates that you installed.

• How to Boot into & Use M1 Mac Recovery Mode

Step 3: Release these keys when you see an Apple logo, spinning globe, or the Utilities window.

Step 4: Enter the requested password if you are prompted to enter a firmware password or the administrator's login password.

• Recover/reset your forgotten Mac password

• Mac won't accept correct password, what to do?

Step 5: Decide if you want to clean install the system, or just reinstall macOS without losing your original data.

If you want to factory reset the Mac for selling or giveaway, or the startup disk becomes corrupted, you might want to erase the startup disk before reinstallation. This guarantees a fresh and clean installation as it wipes all your personal data on the disk.

• How to factory reset your Mac?

• How to reset your M1 Mac to factory settings?

If you only want to reinstall macOS because the original operating system is not working as you expect, you might want to keep your personal data intact. In case files are deleted or lost by accident during macOS reinstallation, you should have a backup of your data or getting files off first.

• How to get files off a MacBook that won't turn on?

Step 6: Either after erasing the startup disk or getting files off the Mac, you can then go back to macOS Utilities and choose Reinstall macOS. Check this post to find all macOS versions and know which one you are going to reinstall.

Step 7: Follow the on-screen instructions and choose a disk to reinstall the OS.

  • If the internal startup disk is not showing up, or the installer says that it can't install macOS on your computer or volume, you might need to back up files and then erase your disk.
  • If the installer asks you to choose Macintosh HD or Macintosh HD - Data when installing macOS Catalina, choose Macintosh HD.

Other ways to install macOS

Apart from reinstalling macOS from macOS Recovery mode, you have other options according to your situations.

  1. Get released macOS versions or updates by App Store or Software Update preferences.
  2. Get macOS beta (such as macOS Monterey that might be buggy now) through Apple’s developer website.

Whatever your situation of reinstalling macOS is, you should always retrieve your data from the Mac before any further movement. After all, you can't tell if you want it back or not in the future.

After months of waiting, macOS Big Sur was released in November 2020. No matter how great macOS Big Sur is, you can experience performance issues as you update your Mac. The good thing is you can downgrade to the previous macOS version.

There are two ways to revert from Big Sur to Catalina. The first one involves restoring a Time Machine backup. The second, which is a bit lengthy, explains how to downgrade to Catalina using a bootable installer. Whichever way you choose, we'll provide step-by-step instructions to help you downgrade.

Open this article on your phone to make sure you do everything step-by-step.


How to downgrade from macOS Big Sur using Time Machine

If you’ve backed up your Mac with Time Machine before upgrading to Big Sur, downgrading to Catalina will be easy. Here’s how to downgrade from macOS Big Sur to Catalina using Time Machine.

Reinstall

1. Back up your data

First, back up everything. Your Mac probably contains your personal data and documents that you don’t want to lose. So, to keep those alive after the downgrade, you need to back up your data.

Reinstall Macos Catalina From Big Sur

You can use Google Drive, iCloud Drive, or any other cloud you prefer. After the backup is done, you can move on to the next step.

Before you begin reverting your Mac to macOS Catalina, it’s worth trying fixing performance issues on macOS Big Sur. Maybe you won’t need to downgrade at all.

CleanMyMac X can help identify and solve performance problems on your Mac. It’s a dedicated Mac cleaner that clears old junk and runs optimization tasks. It’s notarized by Apple, which means it’s safe for your Mac. Get CleanMyMac X for free to run a quick performance scan.

2. Erase your Mac’s hard drive

The first step is plugging your Mac into power (the downgrade process may take a while, and you don’t want your Mac to power off unexpectedly).

You’ll need to erase your Mac’s drive. This will remove everything from your Mac, but you can restore your data later from a Time Machine backup.

  1. Restart your Mac (Apple menu > Restart).
  2. Hold Command-R when your Mac’s rebooting. The Utilities menu should appear.
  3. Choose Disk Utility.
  4. Click Continue and select Startup Disk (usually located at the top of the list ).
  5. Press Erase.
  6. Select the APFS file format.
  7. Choose GUID Partition Map and confirm.

Wait for the process to complete. Only after every piece of data is removed, can you clean install macOS Catalina.

3. Use Time Machine to restore your backup

You can now restore all your files and data and bring your Mac back to the condition it was in before you installed macOS Big Sur.

If your Time Machine backup is stored on the external drive, plug it in your Mac.


So, to restore your Time Machine Catalina backup:

  • Restart your computer and hold Command-R when it reboots.
  • Select the Restore From Time Machine Backup option on the Utilities window.
  • Press Continue.
  • Choose your Time Machine backup disk.
  • Select the backup you want to restore from. Choose the most recent backup that occurred before you installed macOS Big Sur.
  • Then, select a destination disk, where the contents of your backup will be stored.
  • Click Restore and press Continue.

The process may take some time. Your Mac will restart running macOS Catalina.

How to downgrade from macOS Big Sur using a bootable installer

If you didn’t back up your Mac with the Time Machine, it’s too bad. But, you can still downgrade to the previous OS version. Just follow the instructions.

1. Back up your files and data

Backing up your data is important. It prevents you from losing all the files and data that have existed on your Mac's drive for a while. So, don’t forget to back up your Mac before you start downgrading to Catalina.

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2. Create a bootable installer

A bootable installer will help you safely roll back to Catalina. Here’s how to create a bootable installer:

  1. You can go to the App Store and search for Catalina, then download it. Quit the installer, if it tries to install the OS.
  2. If your Mac already runs macOS Big Sur, download the macOS Catalina here.
  3. Get an external hard drive that has at least 12 GB of available storage and plug it in your Mac.
  4. Launch the Disk Utility app and erase your hard drive selecting Mac OS Extended format.

Now, it’s time to transfer your Catalina installer to your hard drive:

  1. Open Terminal (Applications > Utilities).
  2. Paste this command and press Enter:

sudo /Applications/Install macOS Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

The downloaded file, which is your bootable Catalina installer, should be in your Applications folder. MyVolume is the name of the hard drive; if your hard drive or flash drive has a different name, replace MyVolume with the name of your hard drive.

  1. If prompted, enter your administrator password and press Enter again. Terminal won’t show anything when you type your password.
  2. Follow the instructions that appear in the Terminal.
  3. When Terminal says “done”, your hard drive should have the same name as the installer you downloaded (for example, Install macOS Catalina).

Quit Terminal and eject the hard drive.

Install macOS Catalina

Now, you can roll back from macOS Big Sur using the bootable installer.

  • Plug your hard drive (which is now your bootable installer) into your Mac.
  • Open System Preferences > Startup Disk. Choose your bootable installer as a startup disk and press Restart.
  • Your Mac should start up to macOS Recovery.
  • Make sure your Mac has an internet connection to download firmware updates (you can use the Wi-Fi menu in the menu bar).
  • In the Utilities window, select Install macOS.
  • Click Continue and follow the on-screen instructions.

Your Mac will then start installing macOS Catalina and will restart when it’s done.

Mac runs slowly after the update?

If your Mac is slow after the update, but you don’t want to perform this lengthy process and revert to the previous OS, you could try a quick solution. CleanMyMac X has a helpful Maintenance feature that could fix all possible problems on your Mac.

How To Downgrade Big Sur To Catalina

Reinstall Macos Catalina From Big Sur

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  1. Open CleanMyMac X.
  2. Go to the Maintenance module.
  3. Press View All 9 Tasks.
  4. Check the boxes next to the maintenance tasks you want to run.
  5. Press Run.

Reinstall Macos Catalina From Big Sur Free

Wait till CleanMyMac X runs the set of fixes to speed up your Mac.

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Reverting to the previous macOS may seem like a terrifying task. But if you open this article on your phone or another device and follow the instructions, it will be much easier and faster. Don’t forget to clear your Mac before the backup – you will save a lot of free space and remove old clutter that slows down your machine.

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