First, one question is why you want to switch to EFI-mode booting. Based on your gdisk
output, it looks like you've got a single-OS installation, so you don't seem to need to coexist with something else. If you can boot in BIOS/CSM/legacy mode already, why switch? As the saying goes, "if it ain't broke, don't fix it." (OTOH, I see no BIOS Boot Partition, so maybe you can't currently boot in BIOS mode....)
Supposing you have a reason to boot in EFI mode, though, let's start at the beginning....
YUMI is not the only tool for creating a bootable USB flash drive. You can also do it with dd
, UNetbootin, Startup Disk Creator, Rufus, and other tools. All of the tools I've named are capable of creating an EFI-bootable USB flash drive, with the caveat that EFI implementations differ, so what works on one might not work on another. Some tools also have options that can affect how well a created disk will work, either in general or on a specific EFI. Thus, creating your installation disk with another tool should enable you to boot it in EFI mode (assuming, of course, that your computer uses an EFI rather than a traditional BIOS). That said, if you've already installed, re-creating your boot medium and re-installing is overkill....
If you have no other bootable OS on the computer, one solution is to install an EFI boot loader as EFI/BOOT/bootx64.efi
on the EFI System Partition (ESP; your /dev/sda1
). This is easily done if you're installing by hand, but if you're using a tool like grub-install
, you'll have to move files around manually after the fact. Specifically, the EFI version of grub-install
will put GRUB in EFI/ubuntu/grubx64.efi
(perhaps with shimx64.efi
in the same directory). You'll have to copy files to the right location to get them to launch when you boot the computer. If Secure Boot is inactive, copy EFI/ubuntu/grubx64.efi
to EFI/BOOT/bootx64.efi
. You might also need to copy EFI/ubuntu/grub.cfg
to EFI/BOOT/grub.cfg
, too. If Secure Boot is active, it gets more complex; you must copy shimx64.efi
to EFI/BOOT/bootx64.efi
and copy grubx64.efi
to EFI/BOOT/grubx64.efi
. (Note that all these filenames are relative to the ESP's root, so if you were to mount partitions as shown in your /etc/fstab
, you must add /boot/efi/
to the start of each path.) With a boot loader installed to EFI/BOOT/bootx64.efi
and nothing else referenced in the NVRAM entries, your computer should boot from that "fallback" filename.
Another option is to prepare an Ubuntu installer using one of the tools I mentioned earlier, then boot it in EFI mode. With that done, you should be able to run Boot Repair in EFI mode, so it should be able to set up GRUB in that mode. In fact, even in BIOS mode, Boot Repair should be able to copy EFI files as described in the previous paragraph. (I'm not sure how well this works in practice, though; Boot Repair might just try to do a BIOS-mode repair and not attempt to set up an EFI fallback boot loader.)
Yet another option is to use my rEFInd boot manager to get the process started. You can download the CD-R or USB flash drive version of rEFInd and boot from it. rEFInd should detect your Linux kernel(s) and enable you to boot. If this works, you'll be booted in EFI mode, and you can then install the rEFInd PPA or Debian package to use it permanently (without the USB drive); or you can install GRUB via grub-install
and it should set things up correctly. (Note that you'll need the EFI GRUB package, grub-efi
, installed for grub-install
to set up the EFI version of GRUB.) Whether you install rEFInd or GRUB in this way, it will be able to set up an EFI NVRAM entry, since the boot from the rEFInd USB drive will be into EFI mode, thus enabling the OS to add EFI NVRAM variables.
You first need to figure out whether Windows is booting in BIOS/CSM/legacy mode or in EFI/UEFI mode. See this page of mine for details, but basically, you can check the "BIOS mode" line in System Information; it should read "Legacy" or "UEFI," depending on the boot mode.
With the boot mode known, you need to create a bootable Ubuntu installation USB flash drive that includes the appropriate boot loader. Most (but not all) tools for turning Ubuntu .iso
files into bootable USB media can create mediea with either (or both) BIOS-mode and EFI-mode boot loaders. Rufus is one of the more flexible of tools in this respect; it has three options for boot loader and partition table inclusions. See this page of mine for some more comments on this subject.
Note that installing Ubuntu in EFI mode when Windows is in BIOS mode, or vice-versa, is asking for trouble. Such cross-mode installations can work, but they require considerable expertise to set up.
Best Answer
Force non- UEFI installation
a completely different way to avoid UEFI when installing Ubuntu
works for Ubuntu 18.04 (subsequent upgrade to 20.04 without issues):
Install via MinimalCD !
https://help.ubuntu.com/community/Installation/MinimalCD
Quote from the Ubuntu Official Documentation:
The minimal iso image isn't useful for installing on UEFI-based systems that you want to run in UEFI mode. The mini iso lacks the proper files for booting the computer in UEFI mode. Thus, the computer will boot in BIOS compatibility mode, and the installation will be in BIOS mode.
the installation will be in BIOS mode
this has proven to work.
you can choose your Display (XFCE4, Unity, Gnome, ...) during
installation
choosing server flavour during installation is provided by
tasksel
no UEFI :-) Ubuntu without UEFI