Ubuntu – Unable to boot newly installed Ubuntu 16.04 using UEFI mode

Start a Ubuntu Linux (14.04) Live CD in UEFI mode. ^{In case of a USB boot device, disable "Fast Boot" in UEFI.}

Open a terminal window (Ctrl+Alt+T)

To verify that you are actually running in UEFI mode, use this bash command:

$ [ -d /sys/firmware/efi ] && echo UEFI || echo BIOS

The resulting output should be:

UEFI

In case it says BIOS, reboot into your firmware and correct the boot device preference.

To do the BIOS to EFI/UEFI conversion enter these commands:

$ sudo mount /dev/sda1 /mnt
$ sudo mkdir -p /mnt/boot/efi
$ sudo mount /dev/sda3 /mnt/boot/efi
$ sudo mount --bind /dev /mnt/dev
$ sudo mount --bind /proc /mnt/proc
$ sudo mount --bind /sys /mnt/sys
$ sudo mount --bind /run /mnt/run
$ modprobe efivars
$ sudo chroot /mnt
# apt-get install grub-efi-amd64

Apt-get networking failure?

# rm /etc/resolv.conf
# ln -s ../run/systemd/resolve/stub-resolv.conf resolv.conf
# apt-get install grub-efi-amd64

No apt-get failure

The following extra packages will be installed:
  efibootmgr grub-efi-amd64-bin
The following packages will be removed:
  grub-gfxpayload-lists grub-pc
...
After this operation, 2,399 kB of additional disk space will be used.

# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntu --recheck --no-floppy --debug

Despite ending in error message:

Fatal: Couldn't open either sysfs or procfs directories for accessing EFI variables.
Try 'modprobe efivars' as root.

the next reboot already shows "ubuntu" in the firmware its boot options menu, and boots to the console as before, except for now booting in efi mode:

$ dmesg | grep EFI
efi: EFI v2.31 by American Megatrends
fb0: EFI VGA frame buffer device
EFI Variables Facility v0.08 2004-May-17
fb: switching to inteldrmfb from EFI VGA

In case something goes wrong, https://superuser.com/questions/376470/how-to-reinstall-grub2-efi might help.

It's theoretically possible to use an MBR partition table in an EFI-mode boot; however, almost nobody does this, so it's poorly tested. Also, in my own (brief) tests with this method, it seems to produce more problems related to boot loader naming and NVRAM entries (as managed by efibootmgr in Ubuntu). Thus, it's not something I recommend. The saying "if it ain't broke, don't fix it" probably applies to your case -- you say you'd "like" to convert to EFI-mode booting, but you've provided no reason for this. In the absence of such a reason, I'd say it's inadvisable to do the conversion, since nothing's "broke."

Also, if you set up an EFI-mode boot from an MBR disk, I can't promise that future Ubuntu updates will like it. It's conceivable that the Ubuntu installer or update process would choke, possibly creating serious problems down the line. OTOH, it all might go just fine. That's part of why "untested" in this context translates to "you probably don't want to try this" -- there are just too many unknowns, both now and in the future.

That said, if you must do such a conversion, you can certainly try it with an MBR partition table. If you run into problems with NVRAM entries not "taking," you should then do an MBR-to-GPT conversion. Alternatively, you can just plan to do the conversion from the start. See my Web page on the subject for details. Note that partition table data structures are actually quite simple, and the conversion requires no changes to filesystems. Thus, the odds of a catastrophic failure are quite low. If you use gdisk, a problem is most likely to turn up when the program loads the MBR data structures and converts in memory to GPT. At this point, you'll be warned, or at least be told of the problem if you do a disk verification (v in the main menu), so you can abort the operation before writing anything back to disk. OTOH, no partitioning operation is entirely risk-free, and if a problem does occur, it can be catastrophic, so having backups is wise.