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User profile for user: teri555
teri555 Author
User level: Level 1
83 points

How to make a bootable external High Sierra drive?

I am running Mojave on a MacBook Air 2017 and I need to create a bootable version of High Sierra for one unsupported program on an external USB drive. I followed a link on the App Store, but it only gave an update, not the full install package. I tried getting an installer for Sierra, thinking I could install it on the USB drive and then upgrade, but when I ran it, the USB drive didn't even show up as an option. I tried creating a new volume on my hard drive thinking I could maybe do it from there, but got the same result. What is the best way to do this?

MacBook Air 13″, macOS 10.13

Posted on Jul 23, 2021 3:30 AM

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User profile for user: Eau Rouge
Eau Rouge
User level: Level 8
42,602 points

Posted on Jul 23, 2021 5:39 AM

If you want the full install app for macOS High Sierra

Open your Safari browser and click on the link below.

How to get old versions of macOS – Apple Support


Go to the Download OS section and click on macOS High Sierra

this will redirect you to the App Store High Sierra download page

it should say Get or Download. This will download the Install High Sierra.app

to your Applications folder.


Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.


If the App Store says ‘Open’ then it is detecting a previous download of the install app

go to the Applications folder locate Install macOS High Sierra.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.


Having downloaded the High Sierra installer app you will need to make a bootable USB installer

using the instructions here.

How to create a bootable installer for macOS – Apple Support (UK)

Having made the bootable USB installer boot to the USB and install macOS High Sierra

to the external drive.

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User profile for user: Eau Rouge
Eau Rouge
User level: Level 8
42,602 points

Jul 23, 2021 5:39 AM in response to teri555

If you want the full install app for macOS High Sierra

Open your Safari browser and click on the link below.

How to get old versions of macOS – Apple Support


Go to the Download OS section and click on macOS High Sierra

this will redirect you to the App Store High Sierra download page

it should say Get or Download. This will download the Install High Sierra.app

to your Applications folder.


Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.


If the App Store says ‘Open’ then it is detecting a previous download of the install app

go to the Applications folder locate Install macOS High Sierra.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.


Having downloaded the High Sierra installer app you will need to make a bootable USB installer

using the instructions here.

How to create a bootable installer for macOS – Apple Support (UK)

Having made the bootable USB installer boot to the USB and install macOS High Sierra

to the external drive.

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How to make a bootable external High Sierra drive?

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