#Mac disk utility partition greyed out install
#Mac disk utility partition greyed out full

You should also see the name of the disk such as вЂMacintosh HDвЂ™.

It will look like вЂdiskxвЂ™ where вЂxвЂ™ is an integer starting at 0. From the listing, look in the Identifier column for your disk identifier.

#Mac disk utility partition greyed out full

(Or if you are booting to your own bootable drive with a full system, open Disk Utility from /Applications/Utilities). You can try booting from OS X Recovery (by holding вЂCMDвЂ™ + вЂRвЂ™ keys at startup) or an external drive and use the command line to attempt to unmount or erase the disk:ДЎ) Once booted from OS X Recovery, select Terminal from the Utilities pull down menu. (For example to Erase/Partition the disk).

Attempt again to perform whichever task caused your вЂCouldnвЂ™t Unmount DiskвЂ™ error.

Also perform a permissions repair if required.

Select the вЂFirst AidвЂ™ tab and verify the troublesome disk, repairing if needed.

If you have created your own bootable drive with a full system, open Disk Utility from /Applications/Utilities.

If you have used our method above to create a bootable installer, choose вЂDisk UtilityвЂ™ from the available menu.

Then select the desired external drive from the startup manager screen and press the enter key.

If you have an external bootable disk, connect this to your Mac and power your Mac up whilst holding down the OPTION/ALT key.

Some of the following steps are destructive and will lose ALL data on your drive.

I would strongly recommend at this stage attempting to back up any data that is required before proceeding with the following steps.

#Mac disk utility partition greyed out install

To create your own bootable disk, refer to our blog вЂCreating a Mavericks bootable install diskвЂ™. You can then run Disk Utility from there.ДЄn external drive or a network drive is preferred if it is the internal hard drive you have an issue with, since the OS X Recovery is a partition on the same physical drive which may not be able to successfully unmount or modify your internal disk. So the first thing to do is to startup the Mac from another bootable drive such as an external drive or OS X Recovery. Normally, any вЂCouldnвЂ™t Unmount DiskвЂ™ error is attributed to circumstances where the boot drive is being modified or is being used by an application or process. I have found myself recently experiencing a couple of Macs which would not allow me to repair the directory or permissions in Disk Utility, or erase/partition the drive with an error such as: вЂDisc erase failed couldnвЂ™t unmount discвЂ™ or вЂDisk Erase failed with the error: CouldnвЂ™t unmount disk.вЂ™Д®ven trying to use Network Deployment tools such as AppleвЂ™s Netinstall service or DeployStudio have also failed to deploy due to these errors.