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I've installed Ubuntu on a USB drive using another Ubuntu Live USB.

I've formatted that drive with a single partition and mount point /.

The Live USB then fully installed Ubuntu there, and it finished successfully.

However, I can't seem to be able to boot Ubuntu from that drive.

The Live USB was created using Rufus and was configured to use GPT and boot in UEFI mode, which it does. I also don't have Secure Boot enabled in my UEFI configuration.

What could be the issue that prevents the installed Ubuntu drive to boot? Could it be installed with MBR for BIOS? How do I prevent that during the installation?

If I try to boot in CSM mode, grub shows up in rescue mode.

I've never had an issue booting the Live USB drive.

  • You didn't put an EFI partition on the USB, so it cannot boot in UEFI. (Even if you did, the EFI wouldn't be set up properly bug 1173457). Can you select the "ubuntu" choice from the EFI menu (booting off the grub which was set up on the hard disk)? – ubfan1 Nov 9 '18 at 1:55
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    Following method works for Full USB install with both BIOS and UEFI, has optional NTFS Linux/Windows partition: askubuntu.com/questions/1083330/… – C.S.Cameron Nov 9 '18 at 2:53
  • @ubfan1 the point is for the drive to have grub itself, like it's the only drive that the computer would boot from. Seeing that I can't get it to boot, I can't select anything. – Phaellow Nov 9 '18 at 18:41
  • @C.S.Cameron The method you've linked seems to succeed in creating a bootable drive. However, I can't seem to be able to cut the grub.cfg file from sdx5 to sdx3. Maybe I'm not doing it properly? I was trying to mount sdx3 but I couldn't even get write permissions. In any case, I just want it to boot via UEFI, but just using the Ubuntu installer apparently doesn't succeed in doing so... – Phaellow Nov 9 '18 at 18:41
  • @Phaellow: Are you working as root? If cut paste does not work, copy the file then then change name of original ie zzzgrub.cfg. – C.S.Cameron Nov 10 '18 at 4:08
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The EFI menu (some key at power-up) should offer choices of Windows, ubuntu,... Choose ubuntu. That boots off the hard disk, runs ubuntu off the USB. If that works, make an EFI partition on the USB, and copy everything off the hard disk's EFI to the one on the USB -- now the USB should boot when selected.

Unfortunately, now the PC will not boot without the USB (grub looks for its files, doens't find them since no USB, and fails). Change the boot order with efibootmgr to remove the ubuntu choice, and Windows should be first on the hard disk. So put the USB first in boot order, grub runs, and you should be able to select ubuntu or Windows, without the USB, Windows boots.

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