cannot startup from External Hard Drive
2020 iMac 27 inch with Seagate external hard drive plugged in to usb. Prior to Big Sur I could boot from the external. Won't let me do that anymore. Why and how can I fix it.
iMac Line (2012 and Later)
2020 iMac 27 inch with Seagate external hard drive plugged in to usb. Prior to Big Sur I could boot from the external. Won't let me do that anymore. Why and how can I fix it.
iMac Line (2012 and Later)
You need to enable booting from an external drive.
Start your mac from Recovery by holding down command-R, then select Startup Security Utility and check the relevant box. Restart holding down the Option key as usual and now you should be able to select the drive and boot from it.
You need to enable booting from an external drive.
Start your mac from Recovery by holding down command-R, then select Startup Security Utility and check the relevant box. Restart holding down the Option key as usual and now you should be able to select the drive and boot from it.
Maybe the difference is because my mac is one of those with a T2 chip (I have a 2019 16” MBP). I tried to boot from an installer disk to erase and install Big Sur but couldn’t, and to enable this capability in Startup Security. This was before running Big Sur, so to be clear it seems to be a feature of T2 macs, not Big Sur.
I've heard that macOS Big Sur does, in fact, no longer allow booting from an external drive; for security reasons.
I believe there is a fix but only by reducing security.
But I'm not sure what that solution is; can anyone advice? I think it's a case of issuing a Unix command from Terminal in single-user mode.
UPDATE: I think this is it: https://support.apple.com/en-us/HT208198
I did that. I have a mac with T2 chip and followed directions. Chose my external as startup disk and upon restart it seemed ok, chimed but then chimed a second time and it chose the built in HD to startup with.
I have 4 external SSDs with High Sierra, Mojave, Catalina and Big Sur (backup) that I can boot from with my iMac18,3.
.
Somehow that was preset when I upgraded to Big Sur as I never had to go thru that to enable it.
Thanks, learn something new here every day.;
cannot startup from External Hard Drive