Ubuntu – Boot .efi files from GRUB2

This is a modified post by nerasezi in the Ubuntu Forum

The main source for the UEFI was the Ubuntu UEFI guide

The following are the steps he did:

1. Use a live CD which matches the UEFI architecture. Mostly x86-64. Boot up the live cd (xubuntu or lubuntu. Those are lightweight desktop but it should work with Ubuntu and kubuntu as well).

   Be sure your live system is booting in UEFI mode. You may check it on the UEFI setup, probably under Boot option or similar. In my case it just put the "UEFI" prefix before the device name.

2. Once the live system is running set through the terminal a root password by typing
   sudo passwd root

   Then log out from the default live cd user and log in as root in gui mode. Plug in the hard drive. I use a USB3 portable HDD but in most cases the hard drive is a SATA internal drive. Anyway, be sure you've BACKED UP ALL YOUR DATA, cause the process is going to wipe off everything on the drive. Launch Gparted (a gui tool is much easier than the text one) and select the drive you're willing to install the system into. (Be sure to select the right one!) Point to the top menu and select Device>Create Partition Table... A warning message pops out. Click on Advanced and select "gpt". Say OK A new GPT disk layout had been created. Now you need to create partitions on it. It's very important that you create as the first and primary partition, a FAT32 volume and you need to assign the label EFI to it. Once the partition is created, right click on it and select "manage flags". Check the "boot" flag and say OK. Move on to the creation of the / partition (you may want to separate /home and /boot. Do it as you usually do. In my case I've just created the / partition), and a swap area. Always prefer primary partitions cause with GPT the 4 primary partition limitation has been removed. Close Gparted.

3. Install the system into the hard drive "/" partition and remember to point here the bootloader (GRUB 1.99) to install to. If you've created a separete "/boot" partition, you have to choose that one for the bootloader installation.

4. Here comes the part from the UEFIBooting guide:

   Building GRUB2 (U)EFI

   Download the latest grub2 source code ZIP file. ftp://ftp.gnu.org/gnu/grub/

   Building grub2 requires the following programs to be installed (build dependencies):

   bison autoconf automake flex autogen python (2.x series) (for autogen.sh if building from bzr repo) texinfo help2man gettext (NLS support) device-mapper freetype2 (libs)

   sudo apt-get install bison libopts25 libselinux1-dev autogen m4 autoconf help2man libopts25-dev flex libfont-freetype-perl automake autotools-dev freetype2-demos texinfo efibootmgr

   efibootmgr was added to the software you need to install because you will need it later on.

   For 64-bit (U)EFI:

export EFI_ARCH=x86_64 ./configure --with-platform=efi --target=${EFI_ARCH} --program-prefix="" make

In case you have a 32-bit architecture, check the online documentation at the link I have provided at the top.

Install GRUB2 in (U)EFI systems

Determine your EFI SYSTEM PARTITION. (it should be /dev/sda1 or /dev/sdb1 if is set on the 2nd hd)

Then mount the partition at /mnt/EFISYS (or at any mountpoint you wish). The following code assumes /dev/sda1 to be EFISYS partition.

sudo mkdir -p /mnt/EFISYS

sudo modprobe dm-mod

sudo mount -t vfat -o rw,users /dev/sda1 /mnt/EFISYS

sudo mkdir -p /mnt/EFISYS/efi/grub

Then, build an EFI application for GRUB and copy it and the other modules:

Enter the "grub2 compiled source/grub-core" directory - Default : /usr/lib/grub/{EFI_ARCH}

grub-mkimage -O ${EFI_ARCH}-efi -d . -o grub.efi -p "" part_gpt part_msdos ntfs ntfscomp hfsplus fat ext2 normal chain boot configfile linux multiboot

sudo cp grub.efi *.mod *.lst /mnt/EFISYS/efi/grub

Note : The -p "" option is important for creating a portable grub.efi app. Now create a grub.cfg in /mnt/EFISYS/efi/grub :

sudo touch /mnt/EFISYS/efi/grub/grub.cfg

Make the firmware launch GRUB2 (U)EFI as default

For non-Mac UEFI systems, efibootmgr is used to modify the UEFI Firmware Boot Manager. This requires the kernel to be booted in UEFI mode and that the kernel processor architecture should match the firmware architecture (and 'noefi' is NOT used) for 'efivars' kernel module to be loaded and efibootmgr to access the boot manager variables. Initially the user is required to manually launch "efi/grub/grub.efi" from the firmware console itself if grub2-efi was installed in BIOS mode. Then efibootmgr should be run to create the boot entry.

sudo modprobe efivars

Enter the "grub2 compiled source/grub-core" directory

grub-probe --target=device /boot/efi/efi/grub/grub.efi

Assuming the output the grub-probe to be /dev/sda1

sudo efibootmgr --create --gpt --disk /dev/sda --part 1 --write-signature --label "GRUB2" --loader "\\EFI\\grub\\grub.efi"

In the above command, /boot/efi/efi/grub/grub/efi can be split up as /boot/efi and /efi/grub/grub.efi, which translates to (/dev/sda) -> partition 1 -> \EFI\grub\grub.efi .

1. Open Synaptic and remove all grub packages and install just the grub-efi packages (amd64 for me) and all the necessary dependencies. Once the installation is over, run sudo update-grub in the terminal. You should edit "grub.cfg" from /boot/grub and check that the disk UUID matches your disk and partitions, the voice "insmod part_" and "set root='(hd0," have "gpt" textline. If everything is ok, copy "grub.cfg" to the "efi/grub" on the EFI System Partition. If something i mentioned before, doesn't match, just edit grub.cfg and manually change them values. Then copy the file to the "efi/grub" directory on the Efi System Partition (should still be mounted under /mnt).

   Then when I rebooted the system, a new entry on the Boot tab under the UEFI setup has appeared, named GRUB2 and i set it as the default boot option.

Grub looks for a config file /grub/grub.cfg or /grub/x86_64-efi/grub.cfg (or similar).

NB: It is a path from the TFTP server root. That means even if you run your Grub binary from a path like $tftproot/path/to/grubnetx64.efi, don't try to put the direcotry grub/ to the same directory, but really to your TFTP root: $tftproot/grub/

How to find out

In the Grub console:

grub> cat (memdisk)/grub.cfg
if [ -e $prefix/x86_64-efi/grub.cfg ]; then
    source Sprefix/x86_64-efi/grub.cfg
else
    source Sprefix/grub.cfg
fi

And the important part, what the $prefix is:

grub> echo $prefix
(tftp,x.x.x.x)/grub