I have a Windows 10 laptop that I'd like to use to boot directly to an external USB SSD (Ubuntu), but only when it is present (physically connected) at power-up. Presently, I can only boot to the SSD if I boot Windows first, connect the SSD, and then go to Settings >> Recovery >> Advanced >> Restart >> Use a device. While this does work, it's somewhat cumbersome. I've also tried changing the boot order in BIOS, so that Ubuntu is first (Windows second), but when the SSD isn't connected, it boots to the grub prompt, instead of booting to windows. Anyone know how to get this to work for a seamless boot whether the external USB SSD is connected or not?
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2 Answers
Easily done, if the PC recognizes the external SSD as a boot device -- not all PC's can boot from an external SSD.
Just as you can create a live Ubuntu flash drive with persistence, simply follow the same directions, using the external USB SSD. See also 58 Bits.
When you want to boot from the SSD, use the function key your particular model PC uses to select boot device, perhaps F9 or F12
Note that some old flash USB drives were lethargic, even compared to HDD, and using those, in effect, as a portable PC was possible but irritatingly slow. However, a fast SSD seems much more practical in that use.
answered Jul 13, 2022 at 22:49
Well it sounds like when you install Ubuntu, the installer / you chose to use the EFI system partition (ESP) on the internal drive instead of creating its own on the external one.
The solution can be somewhat distro-specific, but obviously the idea is to prevent the former / current case from happening. If the installer is too "streamlined" / "user-friendly" to allow you to customize whether it should use any existing ESP found on the system, another way would be to disable / disconnect the internal drive temporarily.
Also note that some UEFI firmware might purge boot entry that looks for file that no longer exists, so it might be preferable to use the fallback path (i.e. /EFI/Boot/bootx64.efi / --removable of grub-install) in such case instead of nvram registration.
(It's also UEFI-specific though. IIRC for AMI Aptio, it may not provide boot order setting that comes with an "abstract" boot entry item of "USB drive". In that case NVRAM registration might be instead the way to go, otherwise your "if plugged boot that" plan may not work because the boot order is not "fixed".)
It may not be necessary to re-install the whole system, when e.g. you can allocate some space for a new ESP on the drive (it does not have to be at the beginning of the drive). You can then fix the mountpoint, remove the old boot entry with efibootmgr, and re-install grub, all done in the normal environment after booting the installation. (And optionally clean up the grub files on Windows / internal drive ESP.)
