Reinstall Macos Catalina Without Losing Data

| 15-09-2021
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If you have installed Big Sur, Catalina, Mojave or earlier versions, you may have to reinstall macOS for following reasons:

  • Reinstall When There is New macOS Version Available

Apple keeps working constantly to fix bugs, make performance tweaks, add new features or enhance coding. Therefore, doubtless, there will be new versions of macOS available to upgrade and reinstall.

The steps are as follows: a) Go to Apple menu System Preferences Software Update. B) In the Software Update window, click the Upgrade Now button beside macOS Big Sur. Image: macOS Update from Catalina to Big Sur. C) Once the software is downloaded, macOS Big Sur installer opens automatically. Then how to reinstall macOS without any data loss? To provide a double guarantee to the precious data on your Mac, you can make a copy of the files on your Mac before you perform the reinstallation, or equip your Mac with a data recovery tool that can rescue your data after the reinstallation. Don’t forget that you’ll still need a backup of your data to avoid losing your important files, apps, documents, and other personal data. We hope you were able to successfully downgrade from macOS Big Sur to macOS Catalina or Mojave without any hassle.

  • Your Mac is Running Slow

As we all know, for no specific reason, system reinstallation can magically solve a slow Mac in most cases.

  • Your System Keeps Crashing or Works Improperly

When you continuously see error messages appear on your mac, or your programs randomly crash/freeze for no reason, like FaceTime won't work, Contacts or Calendar shows a delay or mess, blue teeth or WiFi won't connect…Then, you have a good reason to reinstall macOS.

  • You are Going to Sell the Mac

In the case that you want to sell your mac, besides erasing all your personal data and traces on the mac, you will need to reinstall macOS as well.

It is not complicate to reinstall macOS Big Sur or Catalina, but if you want to reinstall macOS without losing data, there are 3 steps you must follow.

Recover Files after macOS Reinstall

  • Recover data lost due to macOS reinstallation, upgrade, downgrade
  • Recover data lost due to accident deletion, formatting, etc.
  • Restore data from both internal and external storage device
  • Recover videos, audios, images, documents, and other 200+ files
  • 5 recovery modes to find files back easily
  • High recovery rate
  • Support Big Sur, Catalina, Mojave and earlier
Free Download

3 Steps to Reinstall macOS Big Sur or Catalina without Losing Data

We all save tons of data on our Mac, so when we decide to reinstall macOS Big Sur/Catalina, the top concern always goes to “will I lost everything if I reinstall macOS”. In fact, reinstallation of macOS doesn’t necessarily cause lost data, it just create a new copy, your existing files and data saved in programs won't be altered or deleted. But just in case of bad luck, we need to do some work on BACKUP, this is crucial for macOS reinstallation without losing data.

Step 1. Prepare Your Mac for Reinstallation.

  • Make enough room for Big Sur or Catalina reinstallation, at least 36GB, so the reinstallation process won't pause or stopped for insufficient space.
  • Also, quit all apps or programs under work, so your Mac is fully geared to reinstall.
  • Check drive conditions. Open Disk Utility and perform the Frist Aid on your hard drive where to reinstall the macOS to make sure your drive is in good condition for reinstallation.

Step 2. Backup All Your Files for macOS Install (Crucial)

Backup is an indispensable step involved in the macOS reinstallation, here are several options to backup your data.

Option One: Using Time Machine

  1. Go to Finder>Application, launch Time Machine and choose “Set Up Time Machine”.
  2. Click “Select Backup Disk” to choose an external hard drive to back up the files.
  3. Then Check the box before “Back Up Automatically”. Also, you can adjust the backup setting in menu “Options”.

If this is the first time you use Time Machine to backup, wait patiently for Time Machine to complete the backup, it will prompt the notification once finishes.

Option Two: Using Hard Drive

  1. Connect your hard drive to Mac.
  2. Open Finder to check if your hard drive is present under “Devices”.
  3. Create a new folder, copy and paste or directly move the items you want to save from Mac to this folder.
  4. Finally, eject your hard drive.

Option Three: Using iCloud Service (Backup Desk and Documents Folders)

  1. Go to Finder>System Preference, click on “iCloud” to bring up its main interface.
  2. Click the “Options” button for “iCloud”, and check the box before “Desktop and Documents Folders”, then click on “Done”.

Most of our mac users prefer to backup all files but apps. So, to save you from troubles of lost data due to macOS reinstallation, you are recommended to keep records of what apps you have installed, the account and password, also, you can take screenshots of the settings.

Step 3. Reinstall macOS Big Sur or Catalina without Losing Data.

Option #1: Reinstall macOS without Losing Data From Internet Recovery

  1. Click the Apple icon>Restart.
  2. Hold down the key combination: Command+R, you will see the Apple logo.
  3. Then choose “Reinstall macOS Big Sur” from utilities window and click “Continue”.
  4. Select your hard drive, click “Install” and wait for end of reinstallation.

Option #2 Reinstall macOS without Losing Data From USB

  1. Download the macOS Big Sur install from Mac App Store onto your Mac;
  2. Then connect the USB flash drive to your Mac;
  3. Open Disk Utility program on your Mac, choose the USB flash drive and click Erase to have a clean drive for the reinstallation;
  4. Open Terminal, copy and paste sudo /Applications/Install macOS Big Sur.app/Contents/Resources/createinstallmedia;
  5. Then add the volume of usb flash drive: --volume /Volumes/MyVolume, replace MyVolume with your usb flash drive name, mine is Untitled;
  6. Press Enter, input password and wait for the process to finish;
  7. Quit Terminal, restart your Mac, hold Command+R when starting Mac until you see the apple logo;
  8. Login into your Mac with password, go to the menu bar>Utilities>Startup Security Utility, enter password again;
  9. Choose Medium Security under Secure Boot and allow booting from external media;
  10. Restart your Mac, in the same time, hold the Option key;
  11. Choose Install macOS Big Sur, click Next and input password, choose Install macOS, continue to finish mac reinstallation from usb.

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What if You Lost Data After macOS Big Sur Reinstallation?

However, losing data after reinstallation still happens. It may result from a interrupted installation (power-off/poor internet connection), corrupt setup, insufficient space or improper actions. Then, what to do if you lost data after reinstallation? Here are 2 methods.

Method 1: Use Cisdem Data Recovery to Recover Data

In the case you didn’t do backup before reinstallation, you will need a dedication data recovery program to find the lost data for you.

Here we recommend Cisdem Data Recovery, a powerful mac program allowing users to recover lost/deleted/corrupted/formatted files from a wide range of external or internal storage devices, no matter the file is lost due to human errors, power-off, reinstallation, upgrade, virus attack or disk crash.

Main Features of Cisdem Data Recovery

  • Recover files lost due to OS reinstallation, upgrade, downgrade;
  • Recover deleted, formatted and lost files;
  • Restore files from internal and external hard drive, USB, SD Card, flash drive, etc.;
  • Restore videos, audios, images, documents, archives, 200+ types;
  • 5 recovery modes: Basic, External Drive, Formatted Drive, Trash, Advanced;
  • Preview files before recovery;
  • Fast scanning and recovery;

Steps to Recover Lost Data after MacOS Reinstallation

  1. Download and install Cisdem Data Recovery on Mac.
    Free Download
  2. Choose a Recovery Mode according to your need.
    If you want an efficient recovery, choose “Basic Data Recovery”, if you want to recover files with a higher success rate, try “Advanced Data Recovery”.
  3. Select the hard drive where you originally stored the files on mac. Then click “Scan”.
  4. Check and preview files found by Cisdem Data Recovery.
  5. Select files to recover.
    Check the box before files that you want to recover, then click “Recover” to find back the lost data caused by reinstallation.

Method 2: Use Time Machine to Recover Data with Backup

If you have backed up your files on mac, you can use Time Machine to restore the lost data.

  • Step1. Go to Finder>Applications>Time Machine, launch it and choose “Enter Time Machine”.
  • Step2. In the popped-up window, use the arrows and timeline to browse the local snapshots and backups.
  • Step3. Find the deleted files, then click “Restore” to recover the lost data caused by reinstallation.

Conclusion

The key to reinstall mac OS Big Sur, Catalina or Mojave without losing data is the backup, since no one can guarantee all data will be perfectly maintained after macOS reinstallation. However, if we unfortunately lost files after macOS reinstallation, Time Machine or Cisdem Data Recovery is helpful to recover them back.

So, do you have any other tips to reinstall macOS without losing data? Please share with more of our mac users.

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.

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.

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.

Can You Reinstall Macos Without Losing Data

  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:

Catalina
  • 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

Reinstall Macos Catalina Without Losing 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.

2. Create a bootable installer

Reinstall Macos Catalina Without Losing Data Storage

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

Reinstall Macos Catalina Without Losing Data Connection

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).

How Do I Reinstall Macos Without Losing Data

Quit Terminal and eject the hard drive.

Install macOS Catalina

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

Reinstall Macos Catalina Without Losing Data Protection

  • 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.

  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.

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

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.