Mac won’t boot after OS (Sierra) update because disk is full? Here’s the fix.

(I wrote this in English in order to help more people.)

Last night I spent two hours fighting after my MacBook got totally stuck after I tried to install macOS Sierra update – without making sure that I have enough disk space to make the update. I downloaded the update from App Store. The update software told me that it needs 200 MB more space to do the update. I removed one program (TorBrowser) and I still did not have enough disk space. Then I removed another program (WhatsApp) and voilá: now the updater told that there is enough space for update and I started updating.

But: there is a bug in the updater: cleaning your disk to have about exactly the minimum required space was not enough. During the update my hard disk was filled to 100 % with 0 Mt free space and nothing worked. I was even not able to boot to safe mode by holding shift key during the boot. The installer started and jammed. Many times. The old OS won’t boot either.

The only way to fix things is to free up space so that the updater will finish its job.

So, here is the fix:

Step 1: Don’t be as stupid as I was. Before installing, be sure that you:

  • Make a backup of your system (easiest way is using external hard drive and Time Machine)
  • make sure that there is couple of gigabytes free space in addition to the minimum requirement of the update software. Move couple of family videos to USB stick. Unlink and delete your Dropbox folder. Or something.

Step 2 (if you googled my blog post you probably failed the first step 🙂: Boot into the recovery mode. Reboot your Mac and when you hear the startup chime, press Command and R until you see the Apple logo with progress bar under it. The progress bar may take couple of minutes to finish. Select language (if asked, I use English for this).

Step 3: You see now four options for restoring from backup, reinstalling OS, using browser to search help and using disk utility. But: from top menu, choose Utilities and Terminal.

Step 4: Enter command diskutil list to find the partition where your stuff is. In my example, it is disk0s2 with 250 GB space:


Step 5: If your disk is not encrypted, enter command diskutil mount disk0s2 (if necessary, replace disk0s2 with your volume name if it is different) and go to step 7.

Step 6 (only if your disk is encrypted): The command in step 5 does not work for encrypted volumes:


But you have to enter command diskutil coreStorage unlockVolume <UUID>, where <UUID> is the volume id I circled here (click for larger image):


Step 7: Now you can go to your home folder with cd command, for me it is cd /Volumes/Macintosh\ HD/Users/linjaaho/ . If you have couple of gigabytes of photos or something in Dropbox, the easiest way to free up space is to enter command rm -rf Dropbox . Remember to unlink your Dropbox so that when your computer reboots, you can reinstall dropbox from clean table and it downloads your files from the cloud.

Warning: be careful with rm -rf command, with it you can delete something important accidentally.

Step 8: Boot (Terminal => Quit Terminal, Apple menu => Restart) and enjoy!

After the installation is finished, the new operating system is smaller: before installing I had about 5 GB free and after 18 GT free!




  1. 1


    This was incredibly helpful, thank you for taking the time to post. You made my day! The pictures and step-by-step instructions made it possible even for a complete rookie to arrive at successful completion.

    • 1.1

      Vesa Linja-aho sanoo

      Nice to hear! Couple of weeks ago I considered 1) will I write this 2) will I write this English. Glad I did!

  2. 3

    Federik sanoo

    Hey I tried your steps and got stuck because it fail when trying to un encrypt the disk.
    any help with this part.
    Thank you!

    • 3.1

      Vesa Linja-aho sanoo

      What error message it gives? Take a picture from the terminal and link it here?

  3. 4

    Eduardo Cachucho sanoo

    I get after loading the disk:
    disk0s2 is a FileVault or Fusion Drive physical volume; use ”disk utility coreStorage list” to find its logical volume, which can then unlock (if necessary) and mount
    The drive is not incrypted.
    On using the above direction I see the logical volume disk name is disk2 but on mounting it and entering the cd command I get ”No suck file or directory

  4. 5

    Nic sanoo


    I followed your instructions and got exactly up to the point in the second screen cap, but after that I get stuck, because I cannot figure out how to get it to list owed any files/folders/documents to pick and delete from. Trying to go to the home folder produces no response. Any advice?

  5. 7

    Martin sanoo

    I have the same problem as Suthep: it says Read-only file system.
    What can I do to change that? Do I have to remount the disk? On other websites, I found something about using the sudo command – but then it says ”Command not found”


  6. 10

    LAURENT sanoo

    Thanks for your useful post 🙂
    Just want to add, that it’s also possible to connect another external drive, mount it (using the command line diskutil mount) and then do a copy/paste from your unaccessible data to the hard drive. Just use cp -r /Volumes/Macintosh\HD/ /Volumes/your-other-drive
    Hope that helps someone 🙂

  7. 12

    Lieke sanoo

    Thanks for this post! I just got stuck at the last step wher you have to insert your home folder… I can not get into my computer and have no idea what the name is… how do I find it?

  8. 13

    Chris sanoo

    I scoured the internet and got only bad advice so THANK YOU for having the right answer. Once I found out that my disk was full, I kept thinking ”If only there was a way to get to terminal I could fix this”. This is a great help. THANK YOU.


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