Unified Extensible Firmware Interface (UEFI) is a modern replacement over the BIOS for booting up operating systems. In most BIOS settings, you can choose whether you want UEFI enabled or disabled.
Ubuntu works best with BIOS, not UEFI. So, if you are only installing Ubuntu on a computer or you have Windows 7 or older on it then you can disable UEFI in the BIOS settings and proceed to install Ubuntu with a
/ partition and a swap partition.
However, if you already have Windows 8 or 10 installed on the computer, it will be using UEFI to boot and so UEFI cannot be disabled. Also, if you intend to install and dual boot with Windows in the future, it may be a good idea to keep UEFI enabled.
If you already have Windows 8 or 10 installed then you will notice an extra 100MB partition named EFI while installing Ubuntu. Do not touch it and proceed with creating a
/ and swap partition. Ubuntu will automatically install GRUB to use that EFI partition for booting.
If you do not have Windows, but want to keep UEFI enabled, then you will need to create a 100-200MB partition and pick its type as boot EFI while installing Ubuntu. The rest of the partitions for Ubuntu are the same. Just remember to create an EFI partition.
If you forgot to create an EFI partition on a UEFI enabled computer and installed Ubuntu, then the installer will fail at the end with this error:
The `grub-efi-amd64-signed` package failed to install into / target/. Without the GRUB boot loader, the installed system will not boot.
Tried with: Ubuntu 16.04