Creating a bootable Installer for Big Sur

Question

Level 1

9 points

Creating a bootable Installer for Big Sur

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

I wanted to create a bootable installer for Big Sur on a flash drive. My understanding is that Big Sur may be a bit buggy plus some of my pile of applications may no longer run. Before I upgrade my iMac drive I wanted to boot from a flash drive and run the system for a while to decide whether I want to upgrade immediately or wait for bug fix releases in the future.

I found and followed the instructions provided by apple in the link above. The instructions as given are incomplete. Under "What you need to create a bootable installer" step, the first bullet tells you how to format the target drive. But an important fact is missing. See the discussion of how to use the Disk Utility to correctly format the drive below. I followed the instructions as written in the HT201372 article, did the "option" reboot and tried to install to my USB drive but I got a message that the target volume lacked a GUID partition. So I had to repeat the entire process as modified below.

The missing Information for the step "What you need to create a bootable installer" bullet one should read: "A USB flash drive or other secondary volume, formatted as Mac OS Extended with a partition scheme of GUID Partition Map ...

When you use the Disk Utility to format your USB drive or external drive, you need to click on the Description node of the drive (the outermost node just above the drive name) then press Erase. This exposes the "Scheme" option from which you select "GUID partition map". Also select "Mac OS Extended(Journaled)". Then press erase. A pictorial of this process is provided in the link below.

https://www.macobserver.com/tips/quick-tip/how-to-format-drive-guid/

I have an Intel processor and followed that set of directions. The other thing I noticed was that I had success in holding down the Option key when powering off/on. Doing a restart while holding the Option key did not work for me. Probably operator error...

Print a copy of both documents before starting. ;)

I called my USB drive BIGSUR and used the following sudo command:

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

I am rebooting now to verify the newly formatted drive will install correctly. I will add another post if I run into further issues.

iMac 27″ 5K, macOS 10.15

Posted on Nov 23, 2020 11:26 PM

Reply

Answer 1

Barney-15E

Level 10

123,020 points

Nov 24, 2020 3:54 AM in response to Blauberre

I’ve created a bootable USB installer from a MBR formatted USB stick. It will format and rename the drive before adding the installer and boot files, so the current format was irrelevant. I haven’t attempted it with Big Sur, though.

The drive where you install the OS has different restrictions than the installer USB Drive.

Reply

Answer 2

Blauberre Author

Level 1

9 points

Nov 24, 2020 4:14 PM in response to Barney-15E

Thanks for your input Barney. I had hoped to install Big Sur on the same USB drive on which the installer resides but it is apparently locked during the install. So while in the Option-key reboot, I was able to format a second USB drive on which to perform the installation of Big Sur. However, after the installation appeared to complete, the startup from that new USB drive hung. I also attempted a restart from the new USB and that appeared to hang at about the same point. I will have to repeat the install to see if I get better results.

So my conclusion is that the information in my first post appears to be correct, i.e. the GUID partition format does permit the creation of a usable, bootable installer but the installer will not install to its own drive. A second USB for Big Sur, itself, is required. More later...

Reply

Answer 3

leroydouglas

Level 10

200,652 points

Nov 24, 2020 4:20 PM in response to Blauberre

Blauberre wrote:

Thanks for your input Barney. I had hoped to install Big Sur on the same USB drive on which the installer resides but it is apparently locked during the install. So while in the Option-key reboot, I was able to format a second USB drive on which to perform the installation of Big Sur. However, after the installation appeared to complete, the startup from that new USB drive hung. I also attempted a restart from the new USB and that appeared to hang at about the same point. I will have to repeat the install to see if I get better results.

So my conclusion is that the information in my first post appears to be correct, i.e. the GUID partition format does permit the creation of a usable, bootable installer but the installer will not install to its own drive. A second USB for Big Sur, itself, is required. More later...

You can create a USBinstaller without issue if you follow the instructions as given:

How to create a bootable installer for macOS - Apple Support

Reply

Answer 4

Barney-15E

Level 10

123,020 points

Nov 24, 2020 4:36 PM in response to Blauberre

I had hoped to install Big Sur on the same USB drive on which the installer resides

That's not how it works. You need an installer USB stick and a drive to install the OS upon.

You can create the bootable installer on any USB stick in any format readable by the OS because the drive is first formatted correctly by the createinstallmedia program.

I have seen it fail to create and fail to identify in the Startup Manager if the drive is plugged into a HUB instead of directly connected to the Mac.

Reply

Creating a bootable Installer for Big Sur

Similar questions