macOS Big Sur : cannot create USB bootable drive

Question

macOS Big Sur : cannot create USB bootable drive

I'm running macOS Big Sur 11.1 on a MacBook Pro 2019 with 64GB RAM and 1TB SSD and want to create an USB bootable installer with a terminal command as communicated on Apple support website.

I'm using a 64GB USB key that I'm formatting with Disk Utilities as Mac OS Extended.

Everything seems to run fine and the Install app is correctly copied to the USB key (12,24GB). However, at the end of the process, the command should make this USB key bootable in order to be able to start on it. At this stage, I get an error : "Making disk bootable... Couldn't extract BaseSystem to path:

/Volumes/Install macOS Big Sur/BaseSystem The bless of the installer disk failed."

Has anyone encountered the same issue and get it solved ?

Thanks to the community in advance :-)

MacBook Pro 16″, macOS 11.1

Posted on Dec 17, 2020 11:50 PM

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Answer 1

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emmanuelfrombruxelles Author

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20 points

Dec 21, 2020 11:37 PM in response to emmanuelfrombruxelles

Solution found : the USB key needs to be plugged into the computer directly. I was using a USB hub. As it seems, this setup was generating the final "boot files" error.

Thanks to the ones that took the time to reply my original question.

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Answer 2

Dec 18, 2020 1:37 AM in response to emmanuelfrombruxelles

The Apple recommended command below worked for me for Big Sur 11.0.1 flash installer done in Mojave (I always reformat the flash drive as Mac OS Extended, GUID) before issuing the command and use Disk Utility's default "Untitled" instead that "MyVolume" at the end of the command.

Maybe you could try to re-download the installer (Ethernet is recommended because Wi-Fi could be flaky although shouldn't error correction take care of that) and maybe use another flash drive? Or maybe that v11.1 currently just has an error?

https://support.apple.com/en-us/HT201372

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Answer 3

Dec 18, 2020 3:19 AM in response to Matti Haveri

Hi, thanks Matti for your replies.

I tried again and have another kind of error :

"Making disk bootable...

Couldn't mount dmg /Volumes/Install macOS Big Sur/Install macOS Big Sur.app/Contents/SharedSupport/SharedSupport.dmg (error code 3840)Couldn't find InstallInfo.plist

The bless of the installer disk failed."

Not sure to understand but maybe the installer is corrupted and I should re-download it again. I tried from Mac App Store but as it sees that I'm already running on 11.1, it doesn't allow to donwload it again. Any idea ?

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