UEFI

[vangelis mouhtsis]

Δες τον Debian τρόπο για οτι έχει σχέση για EFI:

UEFI is a specification for motherboard's firmwares which is replacing
the old BIOS. For now, UEFI motherboards still include a BIOS
compatibility layer.

The UEFI boot process is quite different from the BIOS one. It involves
one specific piece of the motherboard's firmware, the UEFI Boot Manager,
which is able to load boot loaders from FAT file systems on
specially-typed partitions. It can offer a boot menu (boot: Debian from
HDD, Windows from HDD, USB stick, DVD?), which can be configured /from a
running operating system/.

So, basically, to boot a system with UEFI, you need two things:

  * to install an UEFI boot loader on a FAT-formated EFI System Partition;
  * to tell the UEFI Boot Manager to create an entry for that boot loader.


    2  Installation or preparation

If you are installing a new Debian system, read the first part. If you
already have a BIOS-bootable Debian system installed, read the second one.

In both cases you will have to use Debian testing, because stable's GRUB
has problems with UEFI. You can also use Debian stable while taking only
GRUB from testing though.


      2.1  Installation of a new Debian system

There is no installer image for UEFI, so you can either:

  * make your own, by installing an UEFI boot loader to an USB stick,
    which will load a regular installer kernel and initrd;
  * use a regular BIOS installer image, using the compatibility mode of
    your motherboard.

The installer does not provide a convenient way to install an UEFI boot
loader, so you are going to install a regular BIOS boot loader at first,
and switch to UEFI later.

Use the expert mode and format your hard drive with a GUID Partition
Table (GPT). Create a small partition (1 MiB would be far enough), type
it as a BIOS Boot Partition (this is the untitled flag above the
“bootable” one in Partman), do not format it and do not mount it: this
will be needed for BIOS booting. Create another small partition (same
kind of size), type it as an EFI System Partition (this is the“bootable”
flag), format it as FAT and mount it on //boot/efi/: this will be needed
for UEFI booting.

Finish the installation as usual, installing GRUB for BIOS, and boot
your new system.


      2.2  Preparation of an existing Debian system for UEFI

You need to use a GUID Partition Table on your hard drive. If you used
an MBR, you lost; you may try to convert it to GPT using a tool such as
gdisk <http://www.rodsbooks.com/gdisk/>, but that means operating
without a net, loosing your current boot loader in the process.

If there is no space left on your hard drive, use Debian Live
<http://live.debian.net/> to make some. Create a small partition (1 MiB
would be far enough), type it as an EFI System Partition, format it as
FAT and mount it (permanently, using the /fstab/) on //boot/efi/ (that
directory will not exist, so create it first).


    3  Switch to GRUB UEFI

Install the package /grub-efi-amd64/. Prepare it by running the command
(assuming your hard drive is //dev/sda/):

# grub-install /dev/sda

That will do three things:

 1. generate a GRUB image;
 2. install it to the EFI partition at /efi/debian/grubx64.efi/
    (relatively to this filesystem's root, which means
    //boot/efi/efi/debian/grubx64.efi/ in absolute);
 3. /try/ to configure the UEFI Boot Manager (the motherboard's boot
    menu) to load it on start-up

That last step will fail. This is expected, because the UEFI Boot
Manager can only be configured from an operating system that was started
from UEFI. So if you stop here, you get an unbootable system.

Now, copy (a symlink would be relevant here, but that cannot be done on
a FAT file system!) the GRUB image to that other path on the EFI System
Partition: /efi/boot/bootx64.efi/ (again, relatively to the ESP
filesystem's root, which means //boot/efi/efi/boot/bootx64.efi/ in
absolute). This is where the UEFI firmware looks for a boot loader when
it has not been configured for a specific path, typically on removable
media. Reboot to check that…

If that trick worked, you are now on UEFI-booted system. Run
|grub-install| again, which should now succeed to configure the UEFI
Boot Manager. Reboot to check that you get a “debian” entry on the
motherboard's boot menu, and remove /efi/boot/bootx64.efi/ which is no
longer needed.

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