Reinstall Mac Os X Catalina

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

If the target Mac computer already had a macOS or OS X on it, then installing macOS from USB is straightforward and this is called the normal way. Step 1: Insert the macOS bootable USB drive on a USB port of Mac computer. Step 2: Shut down the Mac and wait for 1-2 minutes. This will make sure the Mac is powered off. The App Store using the Apple ID you used on your broken mac. The Purchased section and see if it will let you download Mavericks, this is the only way to get a copy. Of Mavericks these days. Catalina App Store does not show you previous OS Downloads. If you can get Mavericks this way then when the Install Mac OS X is. The correct way to reinstall macOS Catalina is to use your Mac’s Recovery Mode: Restart your Mac and then hold down ⌘ + R to activate Recovery Mode. In the first window, select Reinstall macOS Continue. Agree to the Terms & Conditions. Select the hard drive you’d like to reinstall mac OS Catalina to and click Install.

  • 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.

  • 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;
  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.

Mac Won't Turn on after Update to macOS Big Sur?

Here are 10 solutions to fix 'Mac won't turn on after update to macOS Big Sur, Catalina or other versions'.


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.


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.

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.

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:*



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

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.
How to erase and reinstall macos catalina

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.

Learn more

Reinstall Mac Os Catalina

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.

Reinstall Mac Os Catalina From Usb

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: