How to fix macOS partition not mounted and recover lost data?

Posted by Katrina to Mac Data Recovery on July 6th, 2018

After upgrading to High Sierra, my macOS partition got corrupted. Only Windows was working so I got into Disk Utility from Recovery Mode. Disk Utility can see it (grayed out) and has verified it. How to fix macOS partition not mounted? Any help will be appreciated. Thanks!

macOS partition not mounted issue happens after upgrading to a new operating system, when you turning on your Mac computer as usual, or even during editing a working file. If the macOS partition not mounting in Disk Utility, your Mac computer will become unbootable and all data stored on the computer will be inaccessible.

How to fix macOS partition not mounted and recover lost data?

macOS partition not mounted issue is caused by many reasons, it's difficult for us to point out a specific one. However, you can follow the solutions below to fix the unmountable macOS partition and recover data from it.

Solution 1: Boot into Recovery Mode and repair macOS partition in Disk Utility

Step 1: Restart the computer and hold down the Command+ R keys until the menu screen appears.

Step 2: Select Disk Utility.

Step 3: Select the partition with your macOS, usually the Macintosh HD, from the sidebar.

Step 4: Click First Aid on the top.

Step 5: Click Repair disk.

Step 6: When reparation finished, reboot the computer.

Solution 2: Recover lost data and reinstall the macOS system

If Disk Utility can't repair your macOS partition, you need to reinstall the macOS. But system reinstallation will erase all data stored on the macOS partition, so firstly, you should recover lost data from it.

iBoysoft Mac Data Recovery enables you to recover data from unmountable APFS boot volumes, recover data from corrupted APFS boot drives, recover data from startup drives on macOS Mojave 10.14/High Sierra 10.13/Sierra 10.12/10.11/10.10/10.9/10.8/10.7.

Though the Mac computer will be unable to boot up if the macOS partition is unmounted, you still have two methods to recover lost data from it with iBoysoft Mac Data Recovery.

Method 1: If you have only one unbootable Mac computer

If you don't have another Mac computer, please directly run iBoysoft Mac Data Recovery bootable media from iBoysoft Server and recover lost data from the macOS partition.

Method 2: If you have two Mac computers

You can create a bootable recovery drive and then recover data from the unmounted macOS partition.

1. Download iBoysoft Mac Data Recovery on another Mac computer.

2. Install and launch iBoysoft Mac Data Recovery.

3. Click iBoysoft Data Recovery on menu bar and then select "Create Boot Drive".

iBoysoft Data Recovery create bootable drive

4. Insert a USB drive into the healthy Mac computer.

iBoysoft Data Recovery create bootable drive

5. Follow the wizard to create a bootable recovery drive.

iBoysoft Data Recovery create bootable drive

iBoysoft Data Recovery create bootable drive

6. After that, please insert iBoysoft Mac Data Recovery bootable USB drive into the unbootable Mac computer, and then press the Power button and Option key (⌥) to start the computer up.

iBoysoft Data Recovery create bootable drive

7. Select iBoysoft Mac Data Recovery from the boot options.

8. Follow the wizard to scan for lost data on the unbootable Mac computer.

9. Choose the files you want to get back, and then click Recover button.

After recovering data from the unmountable macOS partition, you can go to Disk Utility in Recovery Mode to erase the partition or drive, then, reinstall an operating system to the partition or drive. Hopefully, your Mac can boot up as normal now.

Learn more: why does macOS partition not mounted?

1. Invalid volume header. The volume header contains much important information, such as volume name and size, starting and ending sectors, used and free spaces, and more. If it gets corrupted, the operating system can't recognize your macOS partition and it can't be mounted.

2. Catalog files damage. If catalog file is damaged, the Mac operating system can't find the partition information and macOS partition not mounting.

3. File system corruption. If the file system information gets lost due to virus attack, power failure and human error, the operating system won't mount the macOS partition as usual.

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