Sierra installation error on late 2015 iMac after SSD replacement

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Sierra installation error on late 2015 iMac after SSD replacement

I recently got a late 2015 27” iMac for free that seemed to need a new hard drive as the original one would not/could not install Monterey OS and had a bit of a lag. I replaced the 2TB HHD with a new “crucial” brand 2TB SSD and started the Mac up with a Sierra boot drive, and it seemed to start right up into disk utilities. From here, I formatted the new SSD and attempted to install Sierra onto it, only to be met with an unexpected error occurred message. I decided to run first aid on the drive and the base system drive, yet hit a bump in the road when first aid decided to putz out on me and not continue to do anything, without the mac being frozen. I shut the Mac off and tried to restart it, but when booting with the USB drive, it popped up with a message that said the .mpkg file was either missing or broken. I cleared the boot and reconfigured it again (boot being made from my windows pc via transmac) only for the same message to appear again. Ideas on what is wrong? Could it be another hardware issue outside of the hard drive itself?

[Re-Titled by Moderator]

Earlier Mac models

Posted on Jan 25, 2025 10:11 PM

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Answer 1

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John Galt

Level 10

159,896 points

Jan 26, 2025 2:14 AM in response to Rocksoups

... (boot being made from my windows pc via transmac) .

You're on your own with that.

Instead of attempting to install Sierra in an unsupported manner none of us can help with, boot the Mac using the key chord that will install "the latest macOS that is compatible with your Mac" as explained in this excerpt from How to reinstall macOS - Apple Support:

...
On any other Mac, if you used Command-R to start up from Recovery, you get the current version of the most recently installed macOS. If you used Option-Command-R, you might get the latest macOS that is compatible with your Mac. If you used Shift-Option-Command-R, you might get the macOS that came with your Mac, or the closest version still available.

That will work, assuming operable hardware. Sierra (and High Sierra for that matter) will be problematic for a number of reasons that go far beyond having used a Windows PC to create something that probably isn't going to work anyway.

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Answer 2

Old Toad

Level 10

217,802 points

Jan 26, 2025 11:26 AM in response to Rocksoups

If probably is due to the system requiring updated firmware which can only be installed on an Apple OEM drive.

If that's the case you'll need to install the system on and external SSD using another Mac that can run the system you want to use on the 2015 Mac. Then connect the external SSD to your 2015 iMac, hold down the Option key and boot up to the select system window. Select the external SSD and you should be able to boot successfully.

Then use Migration Assistant to migrate your user data to the EHD.

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Sierra installation error on late 2015 iMac after SSD replacement

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