I have an old iMac with a brand new disk (completely empty). I do not have the old disk, I just have the new one. Of course, now it can't boot, and the flashing folder with the question mark appears. I need to install a new MacOS (e.g., Mountain Lion?). I have tried the internet recovery, but it's running for more than 30minutes now, and I'm afraid it'll end with an error.

The second option is creating a bootable USB on another Mac running Ventura. However, when I download the file InstallMacOSX.pkg, it looks like I can't create a bootable of Mountain Lion from such a file on Ventura.

What can I do?

UPDATE: the Internet Recovery gave the following error:

apple.com/support -21 06U

  • Knowing the precise iMac model would help. If you're not sure you could use Ultimate Mac Lookup to find it.
    – Tetsujin
    Feb 21, 2023 at 10:30
  • Hi, I've just the iMac without the original packaging. Where can I get the serial number? Probably it is around 2015. It has the CD/DVD drive on the side Not a great info, I know. Feb 21, 2023 at 10:39
  • 2
    The precise model becomes more important for 2011 & before; because 2011 was the very beginning of Internet recovery & 2008 was about the first year you could boot from USB.
    – Tetsujin
    Feb 21, 2023 at 10:56
  • 1
    You might be best to go for El Capitan first, then High Sierra. See apple.stackexchange.com/questions/309399/… & the Apple link in the first paragraph. El Cap can be downloaded directly as a disk image.
    – Tetsujin
    Feb 21, 2023 at 10:59
  • 1
    The links I gave go all the way to how to built a bootable installer. You just have to keep reading…
    – Tetsujin
    Feb 21, 2023 at 14:46

1 Answer 1


I`d say try the Internet recovery. It should download everything and install it. And it might take MUCH longer than 30 minutes. Just give it a try.

Apart from that, your best option might be to create a bootable USB on a different Mac. Here are the steps you can follow to create a bootable USB for Mac OS X:

  1. Make sure you have a USB drive with at least 8GB of storage available.

  2. On the other Mac, open the App Store and download the OS X you need. You may need to purchase it if it's not already associated with your Apple ID.

  3. Once the download is complete, the installer will automatically launch. Quit the installer and make sure it's located in the /Applications folder.

  4. Open the Terminal application (located in /Applications/Utilities/) on the other Mac.

  5. Type the following command into Terminal: sudo /Applications/Install\ OS\ X\ YOUR_OS_X_NAME.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ YOUR_OS_X_NAME.app --nointeraction

  6. The process will take several minutes to complete. Once it's finished, you'll have a bootable USB drive.

  7. Insert the USB drive into your Mac and hold down the Option key while powering on your Mac. This will bring up the startup manager.

  8. Select the USB drive from the list of available startup disks, and then follow the on-screen instructions to install OS X.

  • Unfortunately the internet recovery returned the following error: apple.com/support -21 06U. Feb 21, 2023 at 13:15
  • I can't download the El Capitan in that way and create a bootable stick with createinstallmedia. Feb 21, 2023 at 13:16
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    From the error code, IÄm going to make an assumption here that you exchanged the hard disk? krypted.com/lists/comprehensive-list-of-mac-os-x-error-codes says a "-21" is an IO-Error. Maybe the disk is broken or unsupported by the system?
    – Xenonite
    Feb 21, 2023 at 13:20
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    There`s a similar (unanswered) question here: apple.stackexchange.com/questions/425762/…
    – Xenonite
    Feb 21, 2023 at 13:21
  • Yes the disk has been changed (it's an SSD). But I got it as it is, so I can't recover the old one Feb 21, 2023 at 13:28

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