How to Fix: Can’t Install macOS Because Disk is Locked

This has become a common problem for many. You go to install or reinstall your macOS on your system only to find that you are getting an error stating that your disk is locked. It can be very frustrating since you are planning on writing over everything anyway. So why is it locked?

There are a few different reasons that it could be locked but what you need to do is figure out how to move past this problem so that you can get your OS installed. No worries, there is a way to do this and it’s not too difficult of a process.

My name is Eric and I have been working with computers since I was a kid back in the late 1970s. I’ve installed my share of operating systems over that period and I know how frustrating it can be when you run into roadblocks like this one.

If you would like to learn how to overcome this issue, keep on reading and we will take a look at 

what you need to do to get past this problem.

Unlocking the Disk

There are numerous reasons why your disk may be locked and the installer is not letting you re-install your macOS. You may have a used Mac that you bought or someone gave to you and you don’t know the password, you may have forgotten your password or other possible reasons.

Whatever the reason may be, it doesn’t really matter, the best way to proceed is to use the Disk Utility to erase the disk and start over fresh. In the end, this will be better anyway. You will have a clean formatted disk without any garbage on it that will probably perform better.

CAUTION: If you do already have your own data on the drive and need to save anything, make sure you backup your hard drive first. The procedure we are going to use below will completely erase all data on the drive and you will no longer have access to it.

If you are ready to get started, just follow the steps below:

Step 1: Back up your hard drive if you wish to keep the data currently on it.

Step 2: Start your Mac in macOS Recovery mode. There are two different ways to do this depending on the chipset your Mac has. You don’t have to find out which one your is if you don’t want to. If one method does not work, just try the other.

• Method 1 (Apple chipset): Shut down your Mac. Once it is completely powered down, hold down the power button until you see the message Loading Startup Options. Select Options, click Continue and follow the instructions you see on the screen.

• Method 2 (Intel chipset): Go to the Apple menu and select Restart. As soon as your system begins to start back up hold down the Command and R keys until you see the message Loading Startup Options. Select Options, click Continue and follow the instructions you see on the screen.

Step 3: Once the Recovery app opens up, select Disk Utility and then click on Continue.

Step 4: With the Disk Utility, select the volume you would like to erase on the sidebar.

Step 5: Click Erase in the toolbar.

Step 6: In the Name field, enter a name for the volume.

Step 7: Click on the Format field and select APFS if it has not already been selected.

Step 8: Click on Erase Volume Group.

Step 9: When the process completes, click Done.

Step 10: Get out of the Disk Utility by selecting Disk Utility->Quit Disk Utility.

Your disk has now been erased and your original macOS is gone. Stay in the Recovery app for the next section where you will reinstall macOS. 

I will walk you through these steps or you can continue following the process that you were originally using before you ran into the locked disk issue.

How to Reinstall macOS

If you already had instructions that you were following to install your macOS, you can of course continue with them. If not the steps below will show you how to install macOS Big Sur or whatever macOS option is available for your machine in recovery mode.

Step 1: Select Reinstall macOS Big Sur from the Recovery app window and click Continue.

Step 2: On the next screen, when you are ready, click on the Continue button.

Step 3: Follow the instructions on your screen which will walk you through the process.

Step 4: Once completed your system will restart, follow the initial setup process to get macOS configured on your machine.

Once these steps have been completed your MacBook should be back to its original factory settings. After you have done the initial set up you can then load the data or files you backed up back onto the machine and you can also download and install any apps you want to put back.

Why is My Drive Locked?

The frustration caused by the drive being locked and the need to get your operating system installed has probably led to you asking the question or just wondering why the drive is locked or how it got locked in the first place. There are many reasons this could happen.

The first and most common reason is that the drive has been encrypted. Drive encryption is meant as a security measure so that someone else can’t get a hold of your drive and read the data from it. It also prevents others from easily logging into your computer.

Encryption means that the data on the drive is encoded in a format that can only be read after a password is entered and then decoded. On Mac computers, this is done with FileVault. The encoding and decoding take place behind the scenes so you usually don’t even notice it.

Once you enter your password when you log in, FileVault does the rest. So you could have encryption turned on and not even realize it and this is probably why the disk is showing that it is locked.

Other reasons could have something to do with an improper shutdown of your system, some kind of system process that was taking place and was unable to complete, errors or damage to the data on your drive, or other various reasons.

Whatever the reason for it being locked, the methods above should allow you to erase the data on the disk and then install your new macOS. You can check out the information from Apple support if you would like to find out how FileVault works.

Final Words

Finding that your disk is locked while trying to re-install your macOS or install a new macOS can be extremely frustrating and may make you feel like you are ready to give up on the whole process. 

That is understandable but as we have shown above there is a simple way to get around the problem by completely erasing the drive while in recovery mode. There are a few possible reasons that the drive may be locked but the most probable is that it is encrypted by FileVault.

If you have a chance to try the steps I have shown above, let me know how they worked for you. I would love to hear from you and appreciate any feedback that you may have.