Ubuntu – Installing persistent Ubuntu on USB flash drive alongside internal SSD with Windows 10


I have a laptop with Windows 10 installed on the internal SSD. I wish to install Ubuntu on a 64 GB USB 3.0 external flash drive. I already have a separate bootable flash drive with ubuntu 17.04 on it. When I go through the installation process the partition manager detects all my drives and partitions but refuses to let me install onto the external USB drive without modifying the SSD windows boot partition. Several years ago I had a set up where booting a machine without an Ubuntu 14 USB would take me straight to windows and booting with the USB would take me into a persistent Ubuntu 14 that behaved just like a normal internal drive installation (no file or program or setting loss like live versions). I wish to replicate this. Thank you for your time.

TLDR; I have windows on an internal drive. I want ubuntu on a USB flash drive without touching the internal windows drive in any way. UEFI bios boot order is already configured.

Best Answer

Persistent live Ubuntu in the USB flash drive

An easy solution is a persistent live installation on the USB flash drive. You can do that with mkusb. If you boot live (live-only) with the boot option toram, you can install to the same drive as you booted from. See these links,



Installed Ubuntu in the USB flash drive

But if you want an installed system (installed in the same way as installed into an internal drive), and Windows is installed in UEFI mode, you must disconnect the internal drive. Otherwise the Ubuntu installer will install the grub bootloader into the EFI partition in the internal drive.

You find more details at the following link and links from it.

Try Ubuntu (Kubuntu, Lubuntu, Xubuntu, ...) before installing it


  • A persistent live system is more portable, but less stable, more sensitive to corrupting the file system. So it is important to backup the content of the casper-rw partition regularly.

    • It is possible to update & upgrade most program packages, but not the linux kernel and not the kernel drivers. The version from the image of iso file will be used during boot (before the persistent content from the casper-rw partition is overlaid).
    • It is a bad idea to make a general update & upgrade. It can easily corrupt the file system, and even if it works, the system will be slow if a lot of the programs are running from the overlay.
    • You should only install the program packages that you want, and when you need a new version of Ubuntu, install it from a new iso file. And of you can tweak the system and save data files.
  • An installed system is more stable, but less portable, not as portable as a [persistent] live system.

    • Avoid proprietary drivers unless necessary, because they decrease the portability. (This is typically concerning drivers for the graphics chip or wifi chip).
    • Also, and this may be important for you, an installed system can be completely updated & upgraded, just like a system in an internal drive.
    • But all systems in external drives are very sensitive to corrupting the file system, so also installed systems should be backed up regularly.
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