I am installing Ubuntu on my Mac to exist as in parallel with OS X Yosemite, version 1010.3. The screenshot looks similar to previous questions, e.g. How can I resize a partition with Disk Utility?

However, the GUI for Disk Utility does not give me access to resize my partition. Normally, you can click the righthand bottom corner of the volume and drag. I do not have that option---there are no three lines in the bottom righthand for the cursor to drag.

I cannot manually change the size of the partition in the "Size" box. Normally, you could click/highlight the values and change them. I cannot. The text is "faded".

Why doesn't the Disk Utility GUI allow me to choose the size of the partition? Should I just do this via the Command Line?

EDIT: Doesn't anyone else think it's weird that Apple (via Yosemite) forces you to download Windows if you want to partition your hard drive correctly? Note to Apple: FIX THIS!!!

2 Answers 2


Here are instructions for undoing a Core Storage conversion (source - this method worked for me). It should be non-destructive, but as always, take a backup first!

  1. Boot into Recovery HD. If for any reason you don't have Recovery HD, then you'll have to make a bootable Yosemite drive and boot into that.

  2. In the Menu Bar, select Utilities > Terminal.

  3. Run diskutil cs list. You'll get an output that looks like this (credits to the Ask Different user in my source):

  1. Select your Logical Volume ID (the one highlighted in the screenshot) and copy it to the clipboard.

  2. Run the Terminal command diskutil cs revert Paste-Your-Logical-Volume-ID-Here.

  3. Run diskutil cs list to verify that your computer can't find any CS volumes.

  4. You're done! Now Disk Utility should be able to do everything you need it to do to your HD!

  • I finally had a chance to try this. After following these steps, should I open Disk Utility and partition the HD during the Reboot session? Or will Disk Utility allow me to partition properly (i.e. name the size required, etc.) after I re-start my Mac in normal session? I ask because neither options work. May 24, 2015 at 15:18
  • @ShanZhengYang You should be able to do it from Recovery HD or the bootable drive, whatever you booted from to run the Terminal commands.
    – user24601
    May 24, 2015 at 16:00
  • As in, after you've run the Terminal commands, x-ing out of Terminal should bring you back to the Utilities menu, where you should be able to go into Disk Utility and do the resize.
    – user24601
    May 24, 2015 at 16:47
  • As I discussed with @Froggard in the comments below, the fundamental problem with Disk Utility in Yosemite is that you cannot resize your partition. You can resize, but Disk Utility does not allow me to set the size. That's the problem. Following the above does not allow me to set the size of the partition, as far as I know. So, step 7 above is not wholly correct---the Disk Utility GUI is still not allowing me to set the size of the partition. May 24, 2015 at 22:51
  • When I try to partition the HD with Disk Utility, it only allows me to split the HD in half, 50-50. I would rather like to reserve around 30 GB for Ubuntu. May 24, 2015 at 22:53

The reason is that with OS X Yosemite, the internal OS X installation is converted to a Core Storage volume, which is still not fully supported by Disk Utility. There is a way to do it on the command-line, but I'd suggest first partitioning your drive using Boot Camp Assistant, then quit once partitioning is complete. This will give you a volume to work with. Obviously reformatting for Ubuntu will be needed. I can provide further assistance if this doesn't work for you.

  • This is not a bad idea. Is there any way to use Boot Camp Assistant without having to download Windows support software? At what point does the partitioning taking place? It may be simpler to use the command line.... May 19, 2015 at 22:00
  • IIRC, the partitioning is done before windows support software is downloaded. It needs 28GB of free space though, which is overkill for operating systems not as bloated as Windows. I'll add the command-line procedure as an alternate method. May 19, 2015 at 22:26
  • The easiest thing I've found so far is for the Windows support software to be downloaded on a USB port. I have seen no way around this, unfortunately. May 19, 2015 at 22:31
  • Well, if you can download the software somewhere and then delete it, that would work for your purposes. May 19, 2015 at 22:38

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