I just got a new macbook pro, and I want to swap out the internal hard disk with an SSD. My machine did not come with install media, so I was planning on trying to make some based on the recovery partition.

I have already used sudo chflags nohidden BaseSystem.dmg to get to the BaseSystem.dmg file on the recovery partition, but it is only 456.6MB, far to small to contain the (4.3GB? 4.75GB) Mountain lion install disk image. Where is the disk image hidden?

(I have blank DVDs of both sizes, but no erasable USB sticks.)

  • Why are you not just making a clone of your old hard drive to your new one?
    – Stephen
    Commented Jun 18, 2013 at 15:59
  • It's a brand new computer; There's nothing to save. Plus, I don't have the infrastructure to clone drives. Plus, the drives are not the same size. Commented Jun 18, 2013 at 16:05
  • So you don't have any way to run one of you hard drives externally? The size of the drive doesn't matter when you are cloning a drive. If there was some way to run your new or old hard drive in an external case then cloning the drive would be really easy. And at that point if you are still wanting a fresh install of Mountain lion then you could just do it from the recovery partition on the new hard drive.
    – Stephen
    Commented Jun 18, 2013 at 16:09
  • 1
    The Recovery Partition is a minimal bootstrap that connects to a wi-fi network to download the complete OS X 10.8 install, that's why it is so small. See here for further info: About OS X Recovery
    – bayendor
    Commented Jun 18, 2013 at 16:18
  • 2
    @8bitVet You don't need to worry about the recovery partition at all replacing your HDD, everything is downloaded to restore OSX. Even a new recovery partition is created by the internet recovery.
    – jtheman
    Commented Jun 18, 2013 at 20:40

2 Answers 2


You don't need to worry about having to copy any data, making USB sticks or having the media present. Use Mountain Lion's Internet Recovery procedure, all files is downloaded and installed on the new drive without having any files.

You replace the HDD and start with Command-R...

See OS X Internet Recovery for more info about the procedure, quote:

If you happen to encounter a situation in which you cannot start from the Recovery System, such as your hard drive stopped responding or you installed a new hard drive without OS X installed, new Mac models introduced after public availability of OS X Lion or OS X Mountain Lion, automatically use the OS X Internet Recovery feature if the Recovery System (Command-R method above) doesn't work. OS X Internet Recovery lets you start your Mac directly from Apple's Servers. The system runs a quick test of your memory and hard drive to ensure there are no hardware issues.

OS X Internet Recovery presents a limited interface at first, with only the ability to select your preferred Wi-Fi network and, if needed, enter the WPA passphrase. Next, OS X Internet Recovery will download and start from a Recovery System image. From there, you are offered all the same utilities and functions described above.

Regarding "Where is the [OS X] disk image hidden?", the Recovery Partition is a minimal bootstrap that connects to a wi-fi network to download the complete OS X 10.8 install, that's why it is so small. See here for further info: About OS X Recovery.


So, here's how I got a Mountain Lion Install DVD from the recovery partition. It's a crazy workaround.

I started with this article (http://hints.macworld.com/article.php?story=20110831105634716&query=lion+usb)

  1. Mount the invisible recovery partition.
  2. Mount the invisible BaseSystem.dmg disk image.
  3. Run the Installer from there, targeting a USB stick with >5gb free space.
  4. When the machine reboots, yank the USB Stick out.
  5. After it boots normally, reinsert the USB stick and look around on it for the InstallESD.dmg
  6. Burn the InstallESD.dmg to a DVD
  7. Replace your hard drive
  8. Install from the DVD.

I do not recommend this procedure; It's persnickity and slow. Also, the only advantages it has over making a bootable USB drive is that you don't have to erase your USB stick, and you get a DVD backup installer in the end.

  • Great you solved it. It's funny, I could have been the one ending up in a solution like this. You are too experienced to not try fixing it yourself but not up to date with all changes in technology. Well, having a DVD installer in the end is worth something!
    – jtheman
    Commented Jun 20, 2013 at 12:38

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