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.

Leave a Reply

Your email address will not be published. Required fields are marked *

  • Will

    Thanks a lot!
    The recovery mode unlocked the disk successfully.
    Then got an error about the server, but just restarted from usb and finally installed high sierra.
    This was a 2012 macbook pro.
    Thanks again!

    • Jerry Romero

      Awesome! Glad that it helped.

  • C

    Help! I have a VERY old mac computer – somewhere from 2009-2011. I don’t remember and don’t know how to check. I believe it uses high sierra. About 6 months to a year ago, I frequently used it with no problem. I opened it randomly one day and it put me into recovery mode. I tried a couple of things to fix it but gave up. I haven’t used it in months and opened it again today and it’s still messed up. When I go to my disk to erase it, the erase button is gray and I cannot click on it. I also cannot partition anything. I’m new and confused, but am fine losing data. I don’t have anything important on here, I just don’t know what to do…

    • Eric

      Hi C,
      I am sorry to hear you are having this problem. I know that it can be very frustrating trying to get your machine back up and running. When in recovery mode it should let you erase it since in recovery mode it should not be using that partition. When you go to erase it, make sure that you have the disk selected on the left side of the disk utility. Normally the Disk/partition will be called Macintosh HD, but it could be something different on older systems or it is also possible that someone changed the name of it. If that is still not working, it is possible that there is damage to the data on the drive, which would be why it is booting you automatically into recovery mode. Try clicking on the first aid icon near the top of the screen in the disk utility ( it should be a couple of icons left of the erase icon ) and running that to first repair it. If there is a data issue on the drive, repairing it may allow you to then access it and you may be able to boot your system normally, but you also may be able to then do the erase if you still wish to do so. If this does not work, it could be a sign that the drive has gone bad and it may not be repairable. If this is the case, you may need to get a new drive installed but that can be costly and you may have to make a decision of whether to get a new drive or look for a new Mac either new or used. I hope that this information is able to help you. Good luck and I hope things work out well for you!


  • Andy

    Followed until – Erase process failed. Couldn’t unmount disc: (69888)

    • Eric

      Hi Andy,
      I’m very sorry to hear you are having this issue. I know how frustrating this can be. Are you in recovery mode when trying to do this? This error usually means that the disk is still in use by some process which is strange since you are in recovery mode and it should not be used at that point. Sometimes another reboot will solve the problem. After you have tried the ease and gotten the error, try rebooting into recovery mode once again that then try the process again. It seems like there is a process that is stuck running on the drive and it needs to complete before it can unmount and erase the disk.

      If that does not work you can try forcing it to unmount from Terminal while still in recovery mode. When you are in recovery mode, open a Terminal session from the menu and then run the following command.

      diskutil unmountDisk force /Volumes/VOLUMENAME

      Where VOLUMENAME is your volume name such as “Macintosh HD”

      Once you have done that, go back and try to erase the volume and see if that works. Good luck and I hope that this helps you to get your disk erased.

    • Mary

      I got a second hand computer and am having the same problem! I’ve restarted in recovery mode about 4-5 different times and tried everything I can find on the internet and nothing seems to be working for me! I’m reduced to trying geek squad which is unfortunate because I’m sure they cost a ton!

  • Lola

    Hi there! I’m hoping you can help me because not even the apple support people could. But my uncle gave me a 2011 iMac but he could not remember his password to log into the main account on the Mac. So I couldn’t factory reset it to be my own personal computer. I’ve managed to get to the recovery mode and I’ve already followed all of those steps. But when I try to “reinstall Mac OS X” and click on the hard drive, a tab pops up saying I need to sign in with my iCloud account. After doing so, another tab will pop up not too long after saying “this item is temporarily unavailable”. I’ve tried everything down to “command-option-R”. Please help, I need this Mac for school and it’s still in good condition.

    • Eric

      Hi Lola,
      I am sorry to hear you are having this issue, it sounds very frustrating and I am surprised that Apple support was not able to help you through this. I know that you said you followed all of the steps but I just wanted to confirm that you were able to first erase the disk as shown in steps 3 through 10. This is an important part of the process because this will wipe everything out from your disk and it should no longer need an iCloud password for anything. When erasing the disk make sure that you are erasing the actual volume that has all the data and macOS on it. It is usually labeled as Macintosh HD. If you have not already, maybe try going through the steps again and ensure that the disk does get erased. I hope that this helps and that you can get your system up and running.

  • Summer

    I followed your directions to unlock my disk and it worked. Thank you! I then moved on to reinstalling macOS Sierra. I’ve tried twice and both times after it is close to completion there is an error message reading ‘An error occurred while preparing the installation. Try running this application again.’ I did see on the screen where you choose what operating system to reinstall that I have 243.87 GB available and need 249.2 to install the base system. Could this be the problem? If so, how do I fix it? This is a very old Mac that I’m trying to get into working condition for my son to use. Thank you!

    • Eric

      Hi Summer,
      I’m glad to hear that you were unable to unlock the disk and sorry to hear you are having issues reinstalling Sierra. I am pretty sure that you are correct. This looks like a space issue. Your drive does not have enough space to download and install the macOS. You need to have about 9 GB free to complete the installation. If you are able to log in to the system, you will need to go in and try to clear up some space by removing old files. I am thinking it must be saying that you have used 243.87 GB of 249.2 available on the disk because if you had 243.87 available it would be plenty enough to install the macOS. If you can get into the system, see if you can clear about 4 or 5 GB and then try reinstalling again. If that does not work, and you don’t have anything on the system you need to keep, you might think about just erasing the current volume and then installing the macOS. Good luck and I hope that this can help you to get the system working for your son.

  • Lally

    I have a late 2009 MacBook with high sierra and every time I try to use it all it does is have the recovery screen show up. I think I may have erased the os that was on there and now I can’t figure out how to reinstall high sierra from my usb flash drive. I’m so frustrated right now what should I be doing?

    • Eric

      Hi Lally,
      I’m sorry to hear you are having this issue. It does sound like you may have erased or corrupted the existing macOS. Right now I don’t have an older machine available to check this but you should be able to re-install the macOS from recovery mode. Take a look at the link below from Apple support for information about reinstalling your macOS.

      When in recovery mode, look for an option to install from USB, but it looks like there should also be a way to have your system download the latest macOS that will work on your system and install it.

      I know how frustrating this can be and I hope that this can help you.

  • Tai

    This was unhelpful

    • Jerry Romero

      Hi Tai, can you share with us a bit more details about the issues you faced?

  • Ajmal Hares

    Hi Mr. Eric,

    i tried all options but still i am unable to reinstall my MacBook air, because the drive is still locks

    • Eric

      Hi Ajmal,
      I’m very sorry to hear your drive is still locked. Normally erasing the volume group as shown above, will clear and unlock it. Are you able to complete the steps where you erase the volume group? Please make sure that you are erasing the Macintosh HD volume and make sure the process completes.

  • Clara

    Hi Eric,
    When I go to erase the main Macintosh HD volume the button on the lower left isn’t there. In your pictures you show a button that says erase volume group. But the only buttons I see are on the right… cancel and erase. Thanks for your post!

    • Eric

      Hi Clara,
      I’m sorry to hear you are having this issue. I’m not sure why it will not show the Erase Volume Group button. Do you have APFS selected for the format? Does it show the message stating that The system volume “Macintosh HD” is a member of a volume group… ? What version of macOS do you have installed? Sorry, I don’t have a quick answer for this. I have never seen this happen before. Let me know if you have any other information that could possibly help to determine what is different in this case.

  • Sushil

    Dear Eric Sir,
    I have an old macbook 1342 which was working sluggish but fine with macos high sierra.

    I deleted many apps to make it lighter thought it would speedup.
    And , today I deleted it’s Library completely with the Hope it will be off loaded of its damned sluggishness.
    Now the system ,after start ,goes to MacOS Utilities
    There is no backup on my time machine
    I don’t understand from get help on line
    Have tried first aid many time
    While installing os it again comes to macos utilities while saying disk is locked
    How can I save the data though it’s not important but I would like
    Can u take control of my mac and do the install
    Net is working fine
    By the way, though it doesn’t matter am 72 years old and need this help.

    • Eric

      Hi Sushil,
      I am sorry to hear you are having this issue. Unfortunately, I am not able to take control of your computer. For that, you would probably need to contact Apple support. I do have one idea you can try. It is possible that you have FileVault turned on and that is why it is showing that your disk is locked. You can disable FileVault from recovery mode if FileVault is in fact turned on. Try the steps below and check and if it is turn FileVault off.

      1. Boot your Mac in Recovery mode.
      2. Open the Disk Utility and select your start-up disk.
      3. Click on the File Menu and then select Turn off file encryption.
      4. You will have to enter your password.
      5. Now try the steps for re-installing your macOS and hopefully it will no longer show that it is locked.

      I hope that this can help.

  • Anna

    That was very helpful thank you I thought I was gonna go nuts 🙂

    • Eric

      You’re welcome! Glad to be able to help out.