Obviously, because there is no Debian system on the new system. If I use this USB on a different system and try to boot into Debian, it will throw an error.

While installing, the new ESP partition on the USB also takes note of the Debian system as you can see in the Grub screen. I have a SanDisk SSD and when I used installed Linux on it, the experience was very smooth, almost like the SSD on the system.Дid you notice something in the above Grub screen? I used a system which had Debian installed for creating this Ubuntu USB. The Linux USB may not work with systems with secure boot enabled.ДЄbout the slower experience with Linux on USB, if your system has a thunderbolt port, I advise getting a thunderbolt SSD.When you want to use the Linux USB on a system, youвЂ™ll have to go to the boot settings to boot from the USB (unless the system is set to boot from USB by default).Using a Linux system from USB will always be slower than actual hard disk and SSD.Even if you use USB 3, installing Linux will be multiple fold slower than normal Ubuntu installation.USB 2.0 will be painfully slow for both installing and using Linux. I highly recommend using USB 3.0 for both live USB and the actual Linux USB.Use a USB of 4 GB for the live system and at least a 32 GB USB for the Linux USB.One for live USB and another one where Linux will be installed. Let me clear a few more doubts and add some suggestions: The original ESP partition on the hard disk is untouched.Д¬lever trick, I know. This way, you fool the Ubuntu installer into thinking that there is no existing ESP partition and it will create and use a new ESP partition on the USB. Removing the disk is out of question here.ДЄn easier way out is to remove the ESP flag from the ESP partition before installing Linux on the USB and put it back after installation. If you have a desktop PC, you may remove the hard disk and that could solve the problem but things will be difficult when it is a laptop. The solution or workaround to the bootloader problem is that you do not let the installer know that there is already an ESP partition.

How to install linux on usb key