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My computer is a Lenovo ideapad 700 and I've both Windows 10 (already installed with the laptop) and Ubuntu 14 installed as dual-boot with no problem. I'm trying to install Ubuntu 18.04.4 on an external disk (WD Elements) and I've read/watched some tutorials on how to do it but my computer never boots from it. The tutorials I followed suggested dong it in Legacy mode. So I've changed the BIOS settings to use Legacy Support and Legacy First options. I also turned off secure boot and fast startup.

I used UUI to create a bootable USB flash drive and it could boot successfully. I chose Try Ubuntu and then installed Ubuntu on my external disk. I have made 3 partitions for BIOS boot, swap area and /
my disk partition table
I shut down and unplug the boot USB flash disk, then turn on. It only loads the GRUB menu for the already installed ubuntu and Windows on my machine. When I manually force it to boot from the external disk, it loads Windows
I have tried different things and I browsed the various questions, but I can't figure out where the problem is. So, any guidance is really appreciated

PS: Is my understanding correct that I only need that BIOS Boot partition (located i the first 100 GB) and no need for an EPS partition? Also, it's fine to have it as GPT?



EDIT: I want to avoid removing my internal hard disk

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Hassan
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  • The problem may be arising because you've installed Ubuntu 18.04 in legacy mode while other OSes may be installed in UEFI mode. All OS must be installed in the same mode to appear as an option in the boot menu. – sarru1291 May 22 '20 at 05:16
  • This method works for me in both legacy and UEFI mode, 16.04 and later: https://askubuntu.com/questions/1217832/how-to-create-a-full-install-of-ubuntu-20-04-to-usb-device-step-by-step – C.S.Cameron May 22 '20 at 05:40
  • Here is a simpler step by step for a Full install that works in legacy mode, Try first without the optional partitions, swap and BIOS boot are not required to boot legacy mode. https://askubuntu.com/questions/1119700/how-to-fully-install-ubuntu-on-usb-flashdrive/1119713#1119713 – C.S.Cameron May 22 '20 at 06:02
  • @sarru1293 I know we can’t have OSes installed in different modes in same boot menu and I’ve come across multiple sources saying it wouldn’t be possible to have it installed in legacy mode if other OSes are installed in UEFI, but they are all saying it’s a probability. If it’s known to be like that, I’d stop trying because I’ve put so much time into it. Thanks for the comment – Hassan May 22 '20 at 08:36
  • @C.S.Cameron Thank you for sharing these instructions. However I’d like to avoid removing my HDD – Hassan May 22 '20 at 08:37
  • If you install with the Live USB booted in BIOS mode, (legacy), you don't need to remove your HDD, as long as you are careful to install your bootloader to the USB drive and not overwrite your HDD's boot loader. See Note 2: Hard drive removal, on the first reference. If installed in legacy mode the drive will still boot in either BIOS or UEFI mode. – C.S.Cameron May 22 '20 at 08:59
  • Yes I made sure bootloader was installed to the external one. I will try again without the swap and BIOS partitions as you suggested and see if it works – Hassan May 22 '20 at 09:05
  • Let us continue this discussion in chat. – C.S.Cameron May 22 '20 at 09:06

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