I want to expand my startup disk space from 25gb to 40gb using this guide: http://blog.kyodium.net/2010/11/increase-disk-and-partition-size-in.html

But if I do umount /dev/disk0s2 as the article says then it says the disk is busy. If I do diskutil unmount /dev/disk0s2 like the terminal advices then it says it failed to unmount.

I can't go to disk utility and do this either because then it gives this message: enter image description here

That's why I'm using this article that says you need to use the terminal to expand the disk instead and here is what I've tried:

enter image description here

  • are you trying to do it from with in? while the disk is used to run os?
    – Ruskes
    Dec 24, 2014 at 4:17
  • On what hardware are you running your VM here?
    – nohillside
    Dec 24, 2014 at 21:03
  • Windows, merry christmas btw :P It sure would be a great christmas present if someone could solve this for me :)
    – Simsalabim
    Dec 25, 2014 at 1:16

1 Answer 1


Try booting form external disk:

Create it first with your OS X version.

Attach the USB **boot** drive to the Mac and reboot
Hold down the OPTION key during boot, then select the attached boot drive (typically has an orange icon at the boot menu)
At the boot menu, choose “Disk Utility” (if using an Installer disk, pull down the “Utilities” menu to access Disk Utility)
Go to “First Aid” and verify the disk, then repair if needed
--> Now perform the original task that threw the “Couldn’t Unmount” error
  • I don't understand, I don't have any USB with mac os x on it. I'm running mac os x Mavericks from VirtualBox.
    – Simsalabim
    Dec 24, 2014 at 7:02
  • & how would we guess that? Anyway, you can't resize a disk your booted from, it's like trying to saw off a tree branch while you're sitting on it.
    – Tetsujin
    Dec 24, 2014 at 9:56
  • So I need to create a new disk and install mavericks on that as well on the same machine that I have installed mavericks already on? Not sure if it's possible but I will look into it.
    – Simsalabim
    Dec 25, 2014 at 1:19
  • In order to partition you current disk, you can not have it at the same time running the OS X. Thus you need to use USB to run OSX from it, and then partition your disk. While your current OS X is running from a disk, it wont let you partition the same disk, thus you get the "disk is busy", or unmount the disk errors.
    – Ruskes
    Dec 25, 2014 at 1:28
  • I can do what you suggest even when I have mavericks on an virtual machine (virtual box)? I'm starting to feel like it might just be easier to remove this virtual machine and create a new one and install mavericks from scratch again but this time allocate 40gb or maybe even 60gb from the beginning.
    – Simsalabim
    Dec 26, 2014 at 1:46

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