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Disk does not come out as bootable

I have tried this repeatedly (and for a couple of different OS versions) I cannot get it to work. The process runs, and I get "Install media now available", but under copying boot files, it never says Copy Complete, and the resulting disk is not bootable. Since I can't choose it as a startup disk, I can't use it to reinstall the software.

iMac 27", macOS 10.12

Posted on Jan 17, 2020 1:01 PM

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Question marked as Top-ranking reply

Posted on Jan 17, 2020 2:11 PM

That screenshot is very helpful. What you're doing seems to be ok. Copy complete doesn't appear (in Catalina anyway) but all other indications are identical to what I expect.


Did you follow these instructions: How to create a bootable installer for macOS - Apple Support


Proper formatting and GUID partition map are both critical. The instructions don't really emphasize that fact.


Anyway, those instructions worked for me, for Catalina as well as all installers that incorporate the createinstallmedia code. The resulting device becomes appropriately named, is bootable, and works to install Catalina on Macs that support it, so I don't know why yours isn't working.


Some USB flash drives just don't work well with Macs though. Try another? Connect it directly to the Mac. No hubs. No daisy-chaining.


SD cards work exactly the same, if you happen to have one lying around.


Another thought: creating a Firmware Password prevents starting a Mac from any device other than the one selected in Startup Disk preferences, but the password challenge would appear in that case.

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Question marked as Top-ranking reply

Jan 17, 2020 2:11 PM in response to Susan Riegel

That screenshot is very helpful. What you're doing seems to be ok. Copy complete doesn't appear (in Catalina anyway) but all other indications are identical to what I expect.


Did you follow these instructions: How to create a bootable installer for macOS - Apple Support


Proper formatting and GUID partition map are both critical. The instructions don't really emphasize that fact.


Anyway, those instructions worked for me, for Catalina as well as all installers that incorporate the createinstallmedia code. The resulting device becomes appropriately named, is bootable, and works to install Catalina on Macs that support it, so I don't know why yours isn't working.


Some USB flash drives just don't work well with Macs though. Try another? Connect it directly to the Mac. No hubs. No daisy-chaining.


SD cards work exactly the same, if you happen to have one lying around.


Another thought: creating a Firmware Password prevents starting a Mac from any device other than the one selected in Startup Disk preferences, but the password challenge would appear in that case.

Disk does not come out as bootable

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