How to install a fresh macOS on an iMac with a new hard disk?

Question

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 '23 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. — floatingpurr, Feb 21 '23 at 10:39
See https://support.apple.com/en-gb/HT201634 CD drive would make it older than that, but we do need to know the exact model. — Tetsujin, Feb 21 '23 at 10:43
Already done, but I can't identify any identification number on the Mac case. — floatingpurr, Feb 21 '23 at 10:44
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 '23 at 10:56
Looking at the spec, it should be a 2011 iMac. So, Latest compatible operating system: macOS High Sierra 10.13.6 — floatingpurr, Feb 21 '23 at 10:56
You might be best to go for El Capitan first, then High Sierra. See https://apple.stackexchange.com/questions/309399/how-can-i-download-an-older-version-of-os-x-macos & the Apple link in the first paragraph. El Cap can be downloaded directly as a disk image. — Tetsujin, Feb 21 '23 at 10:59
I'll give it a try. From where can i download El Cap as a disk image to create a bootable usb? — floatingpurr, Feb 21 '23 at 11:04
There is a serial number printed on the underside of the Mac. You can enter the number in at this Apple website to get the model and year of your Mac. — David Anderson, Feb 21 '23 at 12:44
Yes @Tetsujin, for some reason, the Download didn't start. Now I have the dmg, and I'm trying to create a bootable usb stick with hdiutil and dd — floatingpurr, Feb 21 '23 at 12:45
The links I gave go all the way to how to built a bootable installer. You just have to keep reading… — Tetsujin, Feb 21 '23 at 14:46

score 1 · Answer 1 · answered Feb 21 '23 at 13:12

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:

Make sure you have a USB drive with at least 8GB of storage available.
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.
Once the download is complete, the installer will automatically launch. Quit the installer and make sure it's located in the /Applications folder.
Open the Terminal application (located in /Applications/Utilities/) on the other Mac.
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
The process will take several minutes to complete. Once it's finished, you'll have a bootable USB drive.
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.
Select the USB drive from the list of available startup disks, and then follow the on-screen instructions to install OS X.

answered Feb 21 '23 at 13:12

Xenonite

283

Unfortunately the internet recovery returned the following error: apple.com/support -21 06U. – floatingpurr Feb 21 '23 at 13:15
I can't download the El Capitan in that way and create a bootable stick with createinstallmedia. – floatingpurr Feb 21 '23 at 13:16
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From the error code, IÄm going to make an assumption here that you exchanged the hard disk? https://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 '23 at 13:20
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There`s a similar (unanswered) question here: https://apple.stackexchange.com/questions/425762/imac-mid-2011-cant-boot-from-recovery-usb – Xenonite Feb 21 '23 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 – floatingpurr Feb 21 '23 at 13:28
What Mac model do you have EXACTLY? – Xenonite Feb 22 '23 at 08:58
This is something that I can't tell you. I haven't any serial number to check – floatingpurr Feb 23 '23 at 09:53
floatingpurr: Have you installed a fresh macOS yet? Or are you still trying? I assumed the last comment by @Tetsujin provided you will the solution. – David Anderson Feb 23 '23 at 10:46

How to install a fresh macOS on an iMac with a new hard disk?

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