Why legacy bios is visible in boot menu in Aspire 3 A315-54 laptop

LEKHASREE

I am using Aspire3 A315-54,

System Model Aspire A315-54

System Type x64-based PC

Processor Intel(R) Core(TM) i3-8145U CPU @ 2.10GHz, 2304 Mhz, 2 Core(s), 4 Logical Processor(s)

BIOS Version/Date Insyde Corp. V1.04, 16-08-2019

SMBIOS Version 3.0

BIOS Mode UEFI

I am using windows 10 by default. Know I wanna use Linux, and hence I used a USB drive to work on Linux. Pendrive is of 32 GB. I installed ubuntu 16.04 .and worked on it yesterday. after working on Linux I disabled the USB and worked on windows for a while. But again when I wanna use Linux and the USB is inserted no ubuntu is shown in the boot menu list. After watching some videos I knew that boot mode should be in legacy mode.but my no legacy mode is shown in the boot menu. What to do? how to use Linux using USB Drive?
please help me out....Because I have installed Softwares in Linux and used yesterday but suddenly Why isn't it working now?

aphanic

There's no need to change the boot mode to Legacy to use Linux, it's perfectly capable of running under UEFI (after all it's been the standard for quite some years though). The only thing that may be required is to disable Secure Boot depending on the Linux distribution you wish to run because there's no signature in their loader/shim/kernel/modules, etc.

Now, Ubuntu is not precisely very nice when it comes to installing (unpopular opinion for sure, but that's just what I think). Its ubiquity installer will refuse to install in UEFI mode to an external USB if it can't access the internal drive. That's because even if you choose to install to an external drive the EFI partition that is modified is the one in the internal drive regardless.

Think of it as if GRUB were installed there directly, and that may be the reason you're not able to boot into Linux after all. Besides, 16.04, that's really old and things have changed in 4 years (for the better), specially regarding booting in UEFI machines. Ubuntu for example is Secure Boot compatible I believe at the moment.

Get me more info on the following things:

•  The partitions you have inside the internal drive, for that if you can access Windows use DiskPart (type it in start menu and follow this):
  
  
  
  
  
  
• Then, from an administrative Command Prompt (you won't be able otherwise) go to the Z: drive and post a screenshot of what you see:
  
  
  

That way we'll know if Ubuntu has modified the partition or not. Yellow highlights are inputs you need to do, reds are important things to look at.

I can try to replicate an UEFI installation of Windows 10 + Ubuntu 16.04 in a VM if you'd like and see what it actually does, but this is quicker. I'd do it however if we need to do some fixes, to ensure proper guidance on how you have to proceed.

Also, how did you create the live Ubuntu USB stick? Using Rufus from Windows is a tried and true way, it'll take care of partitioning the USB stick so it is bootable both under UEFI or legacy (MBR), maybe even both depending on the image size and its code (for Ubuntu 16.04, it works for both):