Xubuntu Linux can boot from USB disks, even without installing to hard drive. It supports both BIOS and UEFI boot.
For most USB sticks, you can just use UnetBootin after taking the USB from the package.
These detailed steps are not needed with most fresh from package USB sticks. As they are listed very briefly, following them requires knowledge of partitioning and Linux.
- Format USB to MBR, (Master Boot Record). Create a bootable W95 FAT 32 LBA 0x0c partition. You can use gnome-disk-utility aka Disks. It seems that many sticks have suitable formating already when bought from a shop.
- Use UnetBootin to extract files from Xubuntu 16.04.3 LTS amd64 ISO image to USB disk.
- Optionally, add “toram noprompt” to both syslinux.cfg and grub.cfg.
- Boot target computer to boot menu (e.g. F9), select Legacy/BIOS Boot and the name of your USB stick.
- The installed system will boot with the same method (BIOS or UEFI) that was used for booting the live USB that did the install.
Happy booting!