Why do I need a MacOS USB installer?

There are a few reasons why you may need your own MacOS USB installers for your MacKing Mac computer - or any Apple computer for that matter. It pays to have a little under the hood knowledge of your everyday work tools, and it really needn't be daunting to learn.

Having a MacOS installer (or in my case, several legacy systems as well as the current one) on a USB key is a basic get out of jail for various reasons:

• You can install the MacOS of your choice without being online, and it's always quicker than using Apple's Recovery Mode. You can also use them to boot from to partition disks and repair problematic software.

• You can use your USB installer to perform a clean install if need be.

• You can install a discrete duplicate system on a different disk partition or external disk for troubleshooting and maintenance.

• You can install a legacy MacOS for older valuable software that no longer works under the current OS.

My skeleton key

I make music and run a recording studio for a living, and I'm completely dependent on my computer and operating system(s) running smoothly. I'm still running MacOS Catalina, as my work involves running hundreds of third-party software plugins - not all of which are Big Sur compatible (yet). I run six disks on the studio computer - one is my main OS, another has a duplicate OS and I also run OS Mohave in Parallels Desktop, as my accounts programme is still limited to Mohave. I know, it sucks.

My USB skeleton key has got me out of trouble more times than I care to remember....

I have a 128gb USB key that's always to hand, and I've it partitioned into 4 disks. The first three partitions run MacOS Big Sur, Catalina and Mohave respectively and the fourth runs the excellent TechTool Protogo by Micromat - a bootable repair suite. The key cost me around £15, the Micromat repair suite is £120 and the MacOS is all free. £135 for total peace of mind.

What you will need

A USB key drive. I'd recommend a big one - 128gb will do it. I wouldn't  go for a USB C one;- if you have a USB C only Mac, you'll be sure to have an adaptor for old drives, and that way, your key will work on pretty much anything.

• MacOS installer(s). The appropriate links follow below.

• Have your iCloud login details handy (as well as your iPhone for two factor authentication).

• You'll be using the command line createinstallmedia in Terminal (located in your Utilities folder within Applications). Don't be afraid, but be sure to copy the commands exactly as detailed. Terminal is a powerful beast...

Prepare your USB

So you've got your new USB drive - if you're using an old one, copy anything on it to somewhere else because you're going to erase it.

Plug in your new USB key, then open Disk Utility (located in your Utilities folder within Applications). Select your USB key in the left sidebar, then start by erasing the disk using the tab on the menu bar. The format should be set to 'Mac OS Extended (Journaled)', and the scheme set to 'GUID Partition Map'.

I'd suggest partitioning it if you have a large key. Select the Partitions tab in the menu bar, then select the number of partitions you desire using the + - symbols and set the size of each partition. I'd recommend at least 15gb for each partition holding a system. The partition names will usually default to 'untitled', but you can name them what you wish for the purposes of this. This process may take a few minutes. Have a cup of tea. When it's done its stuff, press done.

NB - you will need to replace the term MyVolume in the createinstallmedia command below with whatever name you've given your drive.


MacOS installers

Unless you want to create an installer for the latest system, you won't find older installers on the App Store. They're still available via Apple, but 'hidden', so follow the links and command line instructions below for your desired OS.

NB - make sure to quit the Mac Store app before following the MacOS download links below, and use Safari as your browser.

When you have downloaded your installer, do not install! Click cancel if you have the option, or quit the installer. You'll now find the installer in your Applications folder.

Here is a guide to finding your desired installer -

 

MacOS Big Sur installer

 

As this is the current version of MacOS, you'll find it on the app store. Remember:- once downloaded, do not install. Cancel or quit, and look for the installer in your Applications folder, then follow the command line instructions below.

 

MacOS Catalina installer

 

 

Click here to download Catalina from the App Store. Please use Safari and quit the Mac App Store app first.

Remember:- once downloaded, do not install. Cancel or quit, and look for the installer in your Applications folder, then follow the command line instructions below.

 

MacOS Mohave installer

 

Click here to download Mohave from the App Store. Please use Safari and quit the Mac App Store app first.

Remember:- once downloaded, do not install. Cancel or quit, and look for the installer in your Applications folder, the follow the command line instructions below.

 

MacOS High Sierra installer

 

Click here to download High Sierra from the App Store. Please use Safari and quit the Mac App Store app first.

Remember:- once downloaded, do not install. Cancel or quit, and look for the installer in your Applications folder, the follow the command line instructions below.

 

MacOS Sierra installer

 

Click here to download Sierra. Please use Safari and quit the Mac App Store app first.

Apple provides older systems as a dmg file, and you'll find the installer named InstallOS.dmg in your Applications folder

Double click the file and locate the pkg installer, then follow the command line instructions below.

 

MacOS El Capitan installer

 

Click here to download El Capitan. Please use Safari and quit the Mac App Store app first.

Apple provides older systems as a dmg file, and you'll find the installer named InstallOS.dmg in your Applications folder

Double click the file and locate the pkg installer, then follow the command line instructions below.

 

MacOS Yosemite installer

 

Click here to download Yosemite. Please use Safari and quit the Mac App Store app first.

Apple provides older systems as a dmg file, and you'll find the installer named InstallOS.dmg in your Applications folder

Double click the file and locate the pkg installer, then follow the command line instructions below.


Terminal

You'll find the Terminal app in your Utilities folder (inside the Applications folder).

• Open Terminal

• Copy the text that corresponds to your desired system (see below). Be sure to copy it exactly (including spaces) except for the name that you've given to your drive - i.e., replace MyVolume with the name of your drive.

• Terminal will ask for a password - this is the password that you regularly use as your user password. You won't see the password, or the cursor move as you type it in - then press enter.

• Terminal will ask you if you want to erase the volume (which you do!), so type 'Y'.

• You'll see the process of erasing and copying -

Erasing disk: 0%...10%...20%...30%...

Copying to disk: 0%...10%...20%...

....which can take some time. Have another cup of tea. When it's all done, you'll see the words Copy complete and done.

You now have an installer!


createinstallmedia commands

The createinstallmedia command will differ depending on which OS install you're creating, so be sure to select the correct one.

Once again, please remember to substitute MyVolume with the name of your drive.

 

MacOS Big Sur

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume -- /Applications/Install\ macOS\ Big\ Sur.app

 

MacOS Catalina

sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

 

MacOS Mojave

sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

 

MacOS High Sierra

sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

 

MacOS Sierra

sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ Sierra.app

 

MacOS El Capitan

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

 

MacOS Yosemite

sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ Yosemite.app

 


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