Cannot create USB boot disc

Question

Level 1

4 points

Cannot create USB boot disc

I would like to install my current OS (Mojave 10.14.6) and also the subsequent OS Catalina (10.15.702) onto separate partitions of a 128 GB SanDisk USB stick to boot from to use legacy software with Mojave for when I upgrade my late 2013 iMac’s internal OS to Catalina - the latest OS my iMac will go to. I have downloaded and tried Disk Maker X Pro, and also followed various YouTube tutorials to create a bootable USB containing the 6.5GB Mojave 10.14.6.06 Installer and the Catalina 8.24GB 10.15.702 Installer, and, while Disk Maker X and Terminal both say a bootable USB drive has been created, I highlight a newly-created USB drive icon in the System Preferences Startup Drive panel and reboot, but my 2013 iMac just will not boot into either partition, and my Mac boots instead to its internal drive every time. Any solution please?

iMac 27″, macOS 10.14

Posted on Sep 4, 2022 8:50 AM

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Answer 1

BDAqua

Level 10

250,259 points

Sep 4, 2022 9:35 AM in response to dianarigg

Actually you can Install either to external drives by just running the Installer.

But hold Option key at startup, does that show boot choices?

Do you haveFileVault enabled?

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Answer 2

BDAqua

Level 10

250,259 points

Sep 4, 2022 4:05 PM in response to dianarigg

I'd try a real USB drive...

OWC Mercury Elite Pro: USB 3.2 + FireWire 800 External Drive (macsales.com)

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Answer 3

dianarigg Author

Level 1

4 points

Sep 4, 2022 10:49 AM in response to BDAqua

I held the Option key on boot up but it gave me a choice of booting into my internal 10.14.6 Mojave disc or booting into an orange external disc called 10.13 (High Sierra). My external USB stick has two partitions on it, one with Mojave 10.14.6 on it and the other partition with Catalina 10.15 on it. So I pressed the orange external disc icon (labelled 10.13) and a High Sierra installer opened up. This wasn't wanted so I rebooted into my Mac's internal Mojave drive. File Vault is off but I have my Firewall on Stealth Mode.

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Answer 4

dianarigg Author

Level 1

4 points

Sep 4, 2022 2:32 PM in response to BDAqua

Could the issue be that my USB Mojave and Catalina installer files (on separate partitions) are not the INITIAL version of each OS? They are 6.5GB and 8.24GB though so they're not small updaters. And do you think me having Firewall Stealth mode on could be a problem? I was on the phone with Apple Support earlier and they told me that instead of selecting the bootable USB drive in the Start Up Preferences Window to restart, restart holding down the Opt key. When I did this I was presented with two small images to choose which to which to boot into - my internal Macintosh HD (Mojave) or an orange external disc image labelled OS 10.13 (High Sierra). Neither my Mac nor my USB have High Sierra on and I didn't know what to do next so I panicked, rebooted and returned to my Mac's internal Mojave system. But thanks for your replies anyway.

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