To install Ubuntu in EFI mode:
Use a 64bit disk of Ubuntu (Ubuntu32bit cannot be easily installed in UEFI mode)
You might want to use an EFI-only image to avoid troubles with mistakenly booting the image and installing Ubuntu in BIOS mode.
Use a supported version of Ubuntu. Support for UEFI appeared in 11.10, but has become more reliable in next versions. Support for UEFI SecureBoot appeared in 12.10 and 12.04.2.
Set up your firmware (BIOS) to boot the disk in UEFI mode (see the "Identifying if the computer boots the HDD in EFI mode" paragraph below)
Identifying if the computer boots the HDD in EFI mode
This is possible only if you have already installed Ubuntu on the HDD, or by looking at the BIOS setup (see paragraph below).
From an Ubuntu installed on the HDD (neither liveCD nor liveUSB), open a terminal (Ctrl+Alt+T), then type the following command:
[ -d /sys/firmware/efi ] && echo "EFI boot on HDD" || echo "Legacy boot on HDD"
Remark: if the result is "Legacy boot on HDD", then either the BIOS is not UEFI type, or the BIOS is not set up to boot the HDD in UEFI mode.
Identifying if the computer boots the Ubuntu DVD in EFI mode
Warning: even if your PC boots the DVD in EFI mode, it might boot the HDD in Legacy mode (and the contrary).
When booting on a 64-bit Ubuntu disk:
- If the BIOS is set up to boot the CD in EFI mode, then you will see the screen below:
- If the BIOS is NOT set up to boot the CD in EFI mode, or if the disk is not 64-bit, then you will see the screen below:
Set up the BIOS in EFI or Legacy mode
Some recent computers (>2011) allow to set up the boot either in UEFI mode or in Legacy (not-EFI) mode. The way to carry out this setting depends on the computers, but generally this setting is located in the "Boot order" tab of the BIOS (to access the BIOS screens, it is generally necessary to press a key during the PC startup).
Note: Some BIOSes (e.g. American Megatrends' "Aptio", found on the Asus vivobook series) call Legacy mode "Compatibility Support Module" or simply "CSM".
Remark: Some BIOSes allow one to set up the boot mode for the optical drive separately from the boot mode for the HDD.
For example, below:
the "UEFI Hitachi" line allows to boot the HDD in EFI mode,
the "P1: Hitachi" line allows to boot the HDD in Legacy (not-EFI) mode,
the "P3: DVD" line allows to boot the Ubuntu CD in Legacy mode
the "UEFI: USB" line allows to boot the Ubuntu liveUSB in EFI mode.
Here is a 2nd example of BIOS, simpler, where the "Boot Mode" parameter allows one to choose the boot mode ("UEFI" or "Legacy") for all media (hard disk, CD, USB...) at the same time.
Some other firmwares (BIOSes) propose an "UEFI/Legacy Boot:" option with the following choices: [Legacy only], [UEFI only] and [Both]. This last one boots in EFI mode when possible, then in Legacy mode if no EFI files are detected.
Creating an EFI partition
If you are manually partitioning your disk in the Ubuntu installer, you need to make sure you have an EFI partition set up.
If your disk already contains an EFI partition (eg if your computer had Windows8 preinstalled), it can be used for Ubuntu too. Do not format it. It is strongly recommended to have only 1 EFI partition per disk.
An EFI partition can be created via a recent version of GParted (the Gparted version included in the 12.04 disk is OK), and must have the following attributes:
Mount point: /boot/efi (remark: no need to set this mount point when using the manual partitioning, the Ubuntu installer will detect it automatically)
Size: minimum 100Mib. 200MiB recommended.
Other: needs a "boot" flag.