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usb flashdrive will not boot on mac

I have a Retina 5K Imac circa 214 (system report says "15,1"). Trying to boot from an USB flash drive formatted as MacOS extended (journaled) and GUID Partition Map. Ran "disk utility" on top-level USB disk , it showed bootable=NO. However, disk utility shows "bootable=YES" if I run it on the partition on the USB disk. If I reboot and hold down the Option key I do not see the USB flash drive. I also don't see it on using System Preference's Startup Disk item. Ran "First Aid" from disk utility on both he top-level USB disk and the partition and it does not show anything wrong. I have "Install MacOs Monterey.app" on the USB flash drive. I am running Big Sur on the iMac. Any suggestions?

iMac Line (2012 and Later)

Posted on Jan 29, 2022 9:36 AM

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Posted on Jan 31, 2022 10:27 AM

Read those instructions again, this time more carefully. If you want to create a bootable macOS USB installer you need to use the command line to do so. Copying the "Install MacOs Monterey.app" does just that....it copies the app which is just a standard application with no ability to boot a computer.

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Question marked as Top-ranking reply

Jan 31, 2022 10:27 AM in response to erickdobrasil

Read those instructions again, this time more carefully. If you want to create a bootable macOS USB installer you need to use the command line to do so. Copying the "Install MacOs Monterey.app" does just that....it copies the app which is just a standard application with no ability to boot a computer.

Jan 31, 2022 4:38 PM in response to erickdobrasil

Try using a different USB stick especially a different brand. The quality of USB sticks is extremely poor and Macs can be very particular about the drives used for booting. Also make sure the USB stick was properly erased as GUID partition and MacOS Extended (Journaled) before you issues the Terminal commands to create the bootable macOS USB installer. If you left the USB stick using the MBR partition type (default partition type when purchased), then it won't boot.

usb flashdrive will not boot on mac

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