Creating a Catalina Installer drive

DaveWT

Well-Known Member
I think it is time to do a clean install on my iMac after years of just upgrading the macOS, leaving a lot of increasing cruft behind. I have looked at instructions for doing this, on various "trusted" web sites (iMore, MacWorld etc.) and each site gives a slightly different command to be used in Terminal to accomplish this. The instruction on the iMore site (https://www.imore.com/how-create-bootable-installer-mac-operating-system) was unique in that it says if the target drive on which you wish to do the clean install is formatted for APFS (which mine is) then the thumb drive on which you are trying to create an installer should also be formatted for APFS. None of the other sites made such a claim. So is this an absolutely necessary requirement?
I have formatted the thumb drive as APFS but when I try to run the iMore supplied command I get an error message.

"If you wish to continue type (Y) then press return: Y
APFS disks may not be used as bootable install media.
An error occurred erasing the disk."

So this states that I shouldn't be formatted for APFS in spite of iMore's instruction. Have I misread the iMore instructions? I have now reformatted the thumb drive as MacOS Extended (Journaled) and the process appears to be proceeding properly. But will this thumb drive then be able to install Catalina on a completely erased APFS drive in my iMac?
 
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BilBo

Member
MacWorld has better (less confusing) instructions.
https://www.macworld.com/article/34...-bootable-macos-catalina-installer-drive.html

You’ll still need to reformat the external drive as it’s likely formatted as FAT32, which has a 4GB file size limit IIRC and the Catalina installer is larger than that. HFS+ Journaled should be fine. All the jiggery pokery with Terminal is just a needless hassle. There are free apps available (the MacWorld article mentions one, Install Disk Creator) that will automate the creation of a bootable Catalina installer for you. That’s it. Have fun. o_O
 

DaveWT

Well-Known Member
Thanks for the reply. I have the thumb drive all set up now with the Catalina installer on it, Now I just need the time when I can afford a big window to wipe the internal drive clean and reinstall a clean Catalina (if there is such a thing in the case of Catalina) and then get all my important stuff moved back from backups etc.
 

DaveWT

Well-Known Member
Thanks Chas, One of the articles I read talked about that but I wasn't sure if it was a good safe method so just went the Terminal route. Good to know you consider it safe. Of course I create these installer thumb drives so very infrequently, I guess I would wonder if it is worth getting another app.
 

chas_m

Well-Known Member
I've used Diskmaker X since Lion (which it was originally created to be compatible with), no problems.
 
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