Macbook won't let me unmount drive in order to erase it?

Retrowire

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Jan 27, 2013
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Hello everyone,

So yeah, here I am with my sister in law's macbook pro. She needs it reformatted and to have the OS reinstalled. So I go about the dance of turning it on, holding down CMD + R while it's booting up to gain access to the disk utility.

And when I go to erase the primary drive, it attempts to do so, before giving an error stating that it can't unmount the disk.

So I'm at a roadblock, I don't know what to do here. Any suggestions? The best answer will be selected as such.

Thanks ahead of time.
 

Retrowire

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Jan 27, 2013
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I have no disc's. Are there any other ways?
 

Wups

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Oct 14, 2013
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Hi Retrowire,

You can download the OS X and create a boatable drive from a USB. Boot into the Recovery on the bootable drive and you'll then be able to erase the disk. That is the only way you'll be able to as you're booting off of that Hard Drive already.

- Wups.
 

Retrowire

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How do I boot into Recovery? Holding CMD-R while booting brings me to a utility where I can choose a drive to boot from, but the list of drives is blank.
 

Wups

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That means you don't have a recovery partition.

Chuck the OS X on a USB and create a bootable media disk using the "createmediainstall" command in Terminal.
It will erase the disk anyway when you install the new OS X.
 

Retrowire

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So can I boot up the computer in CMD + R, open the Terminal from there, and then run the createmediainstall command there to put a recovery drive on the USB drive? Care to give me a walkthrough just in case? Thanks for helping, sorry I didn't get back sooner.
 

Wups

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Oct 14, 2013
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Exactly that.
No worries, bud. Follow this:
https://support.apple.com/en-us/HT201372
 
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