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I installed Ubuntu on a large and fast USB drive from a USB thumbdrive on a Mac. The point was to boot the drive by keeping "option" pressed down when starting the Mac, just like I did for the thumbdrive. But the Mac never sees the USB drive upon boot. It sees it once it's started and Ubuntu saw it during installation. I tried the bless command in sereval ways, but it didn't change anything.

During the installation, I asked for Grub to be installed at the root of the USB drive, which in my case was /dev/sda. There is an EFI partition of 200MB that I think is unused on the drive. I'm not sure what to do next. The thumbdrive boots to Ubuntu just by keeping "option" pressed down, so it must be possible.

eje211
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  • Did you create a LiveUSB by downloading the Ubuntu 18.04 or 19.10 ISO from https://ubuntu.com/download then check for download errors following https://tutorials.ubuntu.com/tutorial/tutorial-how-to-verify-ubuntu#0 then make a LiveUSB following these instructions on another Linux PC https://tutorials.ubuntu.com/tutorial/tutorial-create-a-usb-stick-on-ubuntu#0 or on a Windows PC https://tutorials.ubuntu.com/tutorial/tutorial-create-a-usb-stick-on-windows#0 .? Please click [edit] and tell us how you made that LiveUSB. – K7AAY Feb 13 '20 at 23:29
  • Ubuntu's Ubiquity installer in UEFI mode only installs grub to first drive. You may be able to copy the /Boot & /ubuntu folders from first drive to ESP on USB drive if you have created an ESP. With UEFI, all the selection options do not make any changes. I do this when installing to external or second drive. Posted work around to manually unmount & mount correct ESP during install #23 & #26 https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1396379 – oldfred Feb 14 '20 at 00:39

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Actually, it turned out this was the answer I was looking for all along:

https://askubuntu.com/a/946155/13360

It took me a couple of hours to formulate the right thing to search for. But after I tried that, it worked on the first try.

I only had to do the first part, steps 1 to 14. After that, my Mac saw the drive and booted on it.

eje211
  • 131