How to Update/Reinstall macOS Without Losing Data

Tracy King updated on Jan 11, 2024 | Home >Computer Instruction

This page covers the full process of how to update and install the latest macOS Big Sur, Catalina, Mojave, etc. on Mac without losing any data. If you need a detailed guide, follow through this page to get the desired macOS installed on your computer now:

Workable Solutions Step-by-step Troubleshooting
Phrase 1. Preparations 2GB+ memory and 9GB+ storage space left on Mac > 45% + battery > Connect to internet...Full steps
Phrase 2. Change a USB port Start Mac from macOS Recovery > Select "Reinstall macOS" > "Continue"...Full steps
Phrase 3. Recover Lost Data After macOS installation, run EaseUS Mac data recovery software > Scan and recover lost data...Full steps

Applies To: macOS Big Sur, macOS Catalina, macOS Mojave, macOS High Sierra, macOS Sierra, or earlier Mac operating systems

Reinstall macOS Mojave, High Sierra, Sierra without losing data

The need to update or reinstall your macOS always follow the release of a new operating system, the slow performance of your Mac, or a system crash. When it comes to reinstalling macOS, users biggest concern is losing data on their computer.

The good news is that, if you follow the instructions strictly to update your Mac Operating System, the chance to lose data on your Mac is quite slim, since a reinstallation just needs to create a new copy of the OS, your existing files stored on your Mac won't be lost. Thus, as long as you don't choose to erase your startup disk during the reinstallation, you won't lose files. However, you know what "Slim" means - it's not 100% safe and is still at the risk of losing some data.

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.

Preparations you Need to Make Before You Reinstall macOS

To reinstall macOS on your computer smoothly. Follow the tips below to prepare your Mac ready for the new macOS update now:

  • Leave at least 2GB memory and 8.8 GB storage space on your Mac
  • Leave at least 45% battery on your Mac
  • Connect Mac to the internet or WiFi
  • Update your Mac Apps to the latest versions
  • Backup all your personal data and even create backups for your present Mac data through Time Machine

Remember to back up your Mac to an external hard drive for preventing system update failure or unexpected troubles from happening. Then follow the detailed guide below to reinstall Mac OS via macOS Recovery mode, which enables you to reinstall macOS, restore your files from Time Machine, repair or erase a disk, and more.

How to Update & Reinstall macOS Without Losing Data

*Print this page or open this page on another device so you can refer to it later.

Step 1. Start up your Mac from macOS Recovery

  • Turn on your Mac and immediately press and hold "Command + R", "Option + Command + R", or "Shift + Option + Command + R".
  • Release the keys when the Apple logo, a spinning globe, or a pop-up for a firmware password appears.

Step 2. Select "Reinstall macOS" from the Utilities Window and click "Continue".

Step 3. Follow the onscreen instructions to select the hard drive you want to install the OS on and start the installation.

Step 4. Don't put your Mac to sleep mode or close its lid during the installation. It's normal to see your Mac restart several times or the screen is white while you reinstall the Mac OS. Just wait patiently for the process to finish.

How to Update & Reinstall Mac OS Without Losing Data

If data loss occurred after you reinstalled macOS, you can follow the next part to recover your missing files.

Recover Lost Data After macOS Reinstallation

If you have backed up your Mac before the reinstallation, you can retrieve your data from Time Machine, an external hard drive, or somewhere else, depending on the way you used to make the backup. If you haven't created any backups for your Mac, then you'll need the professional Mac data recovery software tool - EaseUS Data Recovery Wizard, to perform data recovery. With the help of this tool, you can easily recover the data lost due to macOS reinstallation:

Step 1. Search for lost files

Select the disk location to search for lost files (it can be an internal HDD/SSD or an external hard drive) where you lost data and files. Click the "Search for lost files" button.

Note: Before data recovery, you'd better click "Disk Backup" from the left sidebar to create a backup of your HDD/SSD to avoid further data loss. After backing up, the software can recover data from your disk backup, and you can use the HDD or SSD again.

Recover Data Step1

Step 2. Go through the scanning results

This software will immediately scan your selected disk volume and display pictures, documents, audio, videos, and emails on the left pane.

Recover Data Step2

Step 3. Select the file(s) and recover

Click the data to preview, and click the "Recover" button to have them back.

Recover Data Step3

There are lots of data recovery tools available. But EaseUS Data Recovery Wizard, one of the best Mac data recovery tools, is our pick. It fully supports all macOS systems including the newest Big Sur, Catalina, Mojave, High Sierra, Sierra, EI Capitan, Yosemite etc. It allows you to restore all lost data with simple clicks. Office files, music, videos, emails or other archives can all be restored on your own. 

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Updated by Daisy

Daisy is the Senior editor of the writing team for EaseUS. She has been working at EaseUS for over ten years, starting as a technical writer and moving on to being a team leader of the content group. As a professional author for over ten years, she writes a lot to help people overcome their tech troubles.

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Written by Tracy King

Tracy became a member of the EaseUS content team in 2013. Being a technical writer for over 10 years, she is enthusiastic about sharing tips to assist readers in resolving complex issues in disk management, file transfer, PC & Mac performance optimization, etc., like an expert.

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