I am facing an unusual situation where I could successfully install Ubuntu on an external drive. However, when I try to boot from the external drive, it is not working. This is not the first time that I have done this, but this is the first time when I am seeing this issue. The partition that I have on this external hard drive is: /dev/sdb1: fat32 (boot,esp) - labeled as EFI partition /dev/sdb2: linux swap /dev/sdb3: ext4 For that matter, when I try to boot from EFI file, this particular drive is not even listed in the grub-boot options. Any suggestion to fix the issue would be appreciated. Also, I had another usb drive, which has been unmounted from the device, but it is still listed in the boot list. May I know what could be the reason for this and how to address it? Thanks.