linux - uefi boot not showing ubuntu / GRUB

I've an acer aspire e 14.

It has a single HDD with 7 partitions:

• EFI system on /dev/sda1


• Something described as "Microsoft Reserved" on /dev/sda2


• Windows 10 FS on /dev/sda3


• Linux FS on /dev/sda5


• Swap on /dev/sda6


• Microsoft Windows Recovery Manager on /dev/sda4


• Free Space on /dev/sda

Now the thing is, I'm sure both windows 10 and linux (lubuntu) are installed on UEFI mode, however there's no entry in the boot order to let me select ubuntu or grub as the prefered boot option.

If I don't do anything at boot it will automatically boot to windows 10 without asking anything.

If I want to boot to ubuntu I have to do the following trick:

1. Insert a bootable USB stick (with grub)


2. Once the computer boots, the grub of usb stick lets me choose between trying the live version of the OS in the USB or installing it, I just press Escape.


3. This brings up a console into which I just type 'exit'.


4. The following screen seems to be the UEFI boot selection, and it lets me choose between booting the USB, an 'unknown device', or windows 10 boot manager. If I choose the USB it just goes back to the screen on step 2. If I choose the last it boots windows 10, and if I choose the 'unknown device' it finally shows the screen of grub that's installed in the computer which lets me choose to boot lubuntu or windows.

I really have no idea as to how to solve this issue, so any suggestion or advice is welcome.

(Edit) Among the things I tried are the following:

• "efibootmgr -v" shows up two entries for the same file (an \EFI\ubuntu\shimx64.efi) one named ubuntu, and the other "unkwnown device" this last one also finish the description with an RC. I tried to change the --bootorder to match both of them before the windows boot manager, to no efect, at restarting I boot to windows, and when going back to linux the boot order is not the one I placed before.


• I tried redbuilding the grub as suggested by SmallLoanOf1M, to the same result, but I noticed a weird thing, my linux has a /boot/efi folder. But when I mounted the EFI system (/dev/sda1) to rebuild grub, what I got was that there is an "EFI" folder (notice the caps), could that be the problem? and if so, how should I solve this without messing up anything?