How can I Install Sierra on a USB from High Sierra

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Level 1

4 points

How can I Install Sierra on a USB from High Sierra

I've got an old 2009 iMac with no hard drive that I use as a secondary display, running Sierra from a USB drive, (main new iMac is running High Sierra) but recently when I shut it down it wouldn't reboot. I formatted the USB drive to reinstall the OS, but I can't install Sierra on it (installer won't launch, error message "this copy of the “Install macOS” application is too old to be opened on this version of macOS), and I no longer have access to a machine running Sierra, which is how I installed it in the first place a few months ago (macbook was updated to high sierra last week).

So how can I get Sierra on this USB drive, to get my old iMac to fire up?

iMac, Mac OS X (10.6.8)

Posted on May 1, 2018 7:33 AM

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Answer 1

Christien01 Author

Level 1

4 points

May 3, 2018 7:43 PM in response to Barney-15E

Ok, so maybe I'm doing this wrong. I made a Sierra boot dive on one usb drive, then I'm booting to that, then using that to install Sierra on another usb drive, to run the is from that drive. The install on the 2nd usb drive is what's taking so long. I'm attempting it again - it's been at it now about 4 hours and this is where it's at:

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Answer 2

Barney-15E

Level 10

112,572 points

May 3, 2018 11:18 AM in response to Christien01

Create a bootable usb install drive and use that to boot the iMac and install Sierra.

How to create a bootable installer for macOS - Apple Support

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Answer 3

May 3, 2018 7:48 PM in response to Christien01

The issue here is that Apple no longer signs the Sierra installer, which forces you to use a later operating system.

You *may* be able to force on the operating system that your iMac came with, using the network boot technique, but I'm not certain an iMac circa 2009 can do this. It's neither quick nor easy.

You may be able to find a local Mac hardware store that is able to help you out, with a replacement hard drive for your iMac, and a bootable OS. If you'd like to see what's involved, check out the iFixit videos on the subject:

iMac Intel Repair - iFixit

specifically:

iMac Intel 21.5" EMC 2308 Hard Drive Replacement - iFixit

These are very good breakdowns, and they come with specific instructions, with parts lists, and some have videos, too.

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Answer 4

Christien01 Author

Level 1

4 points

May 3, 2018 8:05 PM in response to LaughingGoat

I know I can run the old iMac from an os on a usb drive - it was working fine for weeks before I had to shut it down. And reboot it, and somehow the os got corrupted. The issue is that I it finally made that drive on a computer running Sierra. Now I don't have access to a machine running sierra, only high Sierra, and I can't seem to get the old iMac to run high Sierra.

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Answer 5

Christien01 Author

Level 1

4 points

May 4, 2018 12:06 PM in response to Christien01

Ok, I've given up on trying to install Sierra from USB drive #1 to USB drive #2, and I'll see if I can get the old imac to run High Sierra. But now I can't install that - it seems to go fine, then after it needs to reboot I get the prohibited sign, and I can't mount the USB drive via disk utility, so I can't even see what's been written to it. What am I doing wrong?

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