UEFI booting without a bootloader

Head_on_a_Stick · 2015-03-08 23:01:23

Since kernel 3.3 (sorry wheezy!) it has been possible to boot Debian up without a bootloader by using EFI BOOT STUB loading.

To take advantage of this feature simply create an EFI system partition on your hard drive -- it must be FAT-formatted (FAT32 is best) and some motherboards will only read the partition if it is 512MiB in size.

Then boot up the Arch live ISO in EFI-mode, create a directory and mount the Debian root partition* (/dev/sd<x><y>) to this directory:

sudo mkdir /debian
sudo mount /dev/sd<x><y> /debian

Then mount the EFI system partition (/dev/sd<x><z>) and copy over the Debian kernel image & initramfs:

sudo mount /dev/sd<x><z> /mnt
sudo cp /debian/boot/vmlinuz-<version> /mnt/vmlinuz
sudo cp /debian/boot/initrd.img-<version> /mnt/initrd.img

Then write the NVRAM entry (include any kernel parameters after "ro"):

sudo efibootmgr -d /dev/sd<x> -p <z> -c -L "Debian" -l /vmlinuz -u "root=/dev/sd<x><y> ro initrd=/initrd.img

You may have to tweak the order of the NVRAM entries using:

sudo efibootmgr -o xxxx,yyyy,zzzz

Where "xxxx", "yyyy" & "zzzz" are the bootnumbers of the NVRAM entries.

Then write a post-install script for the Debian kernel to copy over the fresh image and initramfs when the kernel is updated:

# /etc/kernel/postinst.d/zz-update-efistub
#!/bin/sh
mount /dev/sd<x><z> /mnt
cp /vmlinuz /initrd.img /mnt/
umount -R /mnt

Then make this script executable:

sudo chmod +x /etc/kernel/postinst.d/zz-update-efistub

This method can be used to convert a non-EFI Debian system to boot in EFI-mode.

* If you have a separate /boot partition mount this instead and miss out the leading "/boot" in the subsequent commands.

EDIT: If you are using this guide to convert wheezy/Waldorf (with a backported kernel) to EFI booting, remove the "-R" flag from the `umount` command in the zz-update-efistuib script.

Last edited by Head_on_a_Stick (2015-07-13 17:46:52)

Joe90 · 2015-03-08 23:18:40

Great howto

Just debian or any distro with the 3.3+ kernel ?

Head_on_a_Stick · 2015-03-08 23:19:33

Thank you!

It works with anything -- I did it with Slackware 14.1 today.

Although it works best with Debian because of the kernel post-install script -- with other distributions that do not have this feature the kernel image & initramfs would have to be copied over manually whenever the kernel is updated (not very often in Slackware).

Last edited by Head_on_a_Stick (2015-03-08 23:21:04)

Sector11 · 2015-07-13 18:48:41

What about dual booting?

Head_on_a_Stick · 2015-07-13 18:55:28

Sector11 wrote:

What about dual booting?

You would have to write a separate NVRAM entry for each system.

For Windows, use:

sudo efibootmgr -d /dev/sd<x> -p <z> -c -L "Windows" -l /Microsoft/EFI/bootmgfw.efi

Sector11 · 2015-07-13 19:36:36

I was just asking ... I'm my computer is too old for UEFI

Doesn't stop me from following the HoaS breadcrumbs and reading everything.

Head_on_a_Stick · 2015-07-13 19:42:18

For multi-boot systems, I would recommend gummiboot

I will write a tutorial for that when I have time.

CrunchBang Linux

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#1 2015-03-08 23:01:23

UEFI booting without a bootloader

#2 2015-03-08 23:18:40

Re: UEFI booting without a bootloader

#3 2015-03-08 23:19:33

Re: UEFI booting without a bootloader

#4 2015-07-13 18:48:41

Re: UEFI booting without a bootloader

#5 2015-07-13 18:55:28

Re: UEFI booting without a bootloader

#6 2015-07-13 19:36:36

Re: UEFI booting without a bootloader

#7 2015-07-13 19:42:18

Re: UEFI booting without a bootloader

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