How to reinstall software on older machine/How to download MacOS High Sierra (or any older OS on new system)


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Hi all

I am trying to reinstall OS on an older iMac (after erasing the HD).

I need to get hold of the installer for High Sierra so that I can create a usb installer.

I updated my other machine to 10.15 specifically so I could use the new 'softwareupdate --fetch-full-installer ' command in Terminal. However, this has failed with the error 'Update not found".

It seems Apple does not want you to be able to install an older version on a newer machine. But how can I get the OS needed for my older iMac?

Any help appreciated.
 
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Hi Cory

I get the same message from the App store; 'update unavailable'.

I believe this is because there is a block on downloading older OS.

P
 

Cory Cooper

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Hi,

Yes, that could be. Do you have access to a Mac running an older version of macOS?

C
 
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Hi,

Unfortunately, I do not. Do you know of any other way around this?

P
 

Cory Cooper

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Hello,

I tried it here on a MBP running Catalina and got the same message. You should be able to download the macOS Sierra installer from Apple from the link below, as it is a DMG file and doesn't go through the App Store.

How to upgrade to macOS Sierra

You could create USB flash bootable installer for that, install it, then upgrade to High Sierra with the previous link. Or, you would then be able to get the High Sierra installer from the previous link via the App Store, create a USB installer for it, then wipe and install it on your iMac.

Lots of steps, but that should work.

C
 
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Hi Cory

Do you know how I can create the usb installer with the Sierra .dmg/.pkg file? Tutorials normally explain how to create it with the installer file from the app store.

Cheers
 

Cory Cooper

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Ooops...my bad. I forgot about the difference in that particular DMG.

Check your private conversations.

C
 
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One thing that I have done when I followed those procedures, is save the installation programs onto a memory card, so I wouldn't have to go through all of that again.
 
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Thanks Howard that could be helpful in the future, however, I didn't have the foresight on this occasion.

And thanks Cory for helping me find a workaround.

I could mark this solved? I achieved what I wanted. But the question of how to do this with a newer OS remains, it seems apple blocks the ability.

Cheers, P
 
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Yeah, it took me a 2nd need to learn to save those files.

I'm planning on getting the first generation ARM iMac, and apparently won't be able to run older versions of MacOS. I won't be able to do that until one program finally gets converted to 64-bit (the writer has been working on it for over a year). Right now, I boot up to a SSD that has Mojave on it to run that program.
 
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Cory Cooper

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No worries P ;)

Yes Howard...that is the answer. I have a couple of external HDs partitioned with older versions of OS X/macOS, all of my utility applications, third-party installers, and saved Apple full installers. I have several older Macs that can startup from them, which allows me to run diagnostics/troubleshooting utilities, etc. They also have USB connections, with partitions with the bootable installers on them for every version of OS X/macOS from Lion through Mojave.

Always a good thing to have around when you run into trouble or want to perform a clean erase and install of a Mac. ;)

C
 

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