Linux – Is a hybrid Linux USB-Stick for UEFI & legacy BIOS possible

biosbootlinuxuefiusb

my idea is to create an USB-Boot-Stick with Lubuntu that is able to boot on an older BIOS Laptop and an newer UEFI Systems.

This would be quite easy, when the Stick would be setup as a legacy boot device, but I want it to be an UEFI-able device.

Does that make even sense?! Or did I understand the UEFI concept horrobly wrong?
If necessary there can be two diffrent Linux installs (one for UEFI, one for legacy but both on the same drive)
Boot a GPT Device on legacy Bios – will that work?

I can't see clear, it might be just a better idea to have a seperate legacy Linux boot stick, but I am curious to explore the boundries 🙂

So, is my idea of a hybrid linux-uefi-boot-usb-stick that would work with legacy bios possible?

(3) seems to be possible for linux with grub http://www.rodsbooks.com/gdisk/booting.html

Further, I do have an EF00 Partition ready on that stick, aside a Swap, Fat32 and two Ext4 partitions.

(1) seems to be possible too http://www.rodsbooks.com/bios2uefi/

This instructions are however from 2012, some time passed since – does anybody have a working example that is easier?

For other researchers of this topic:

Boot of Windows 7 from GPT disk on non EFI motherboard
Is there any way to boot Windows 7/8 using BIOS on GPT?

http://www.borncity.com/blog/2012/07/25/uefi-emulation-auf-pcs/

UPDATE:

I have managed to create the UEFI part inlcuding secure Boot setup with rEFInd.

Following the given advice, I have used dd to copy gptmbr.bin to my drive, which now seems to do at least something on a BIOS-System: "This is not a bootable disk"

However, I have followed the advice and set the pmbr flag for the disk and the gpt legacy boot flag – still gettin this error, any ideas?

My ESP partition is the second partition on the disk and is setup with efi files.

The Setup:

64GB Space
GPT Partitiontable
Disk has pmbr flag set
1st Partition starts at 16MiB and is about 45GB, a fat32 primary for data
2nd Partition starts around 45GB and is the EFI System(fat32) with a working rEFInd setup
3rd – 5th Partition is home (ext4), swap and root(ext4) of my working Lubuntu 14.04.1

Using dd I have copied the gptmbr.bin of my compiled 6.02 Syslinux to the first 440bytes.

Under parted 3.2 I can see that my partition 2 has a boot and legacy_boot flag.

During boot I get No bootable disk found – if I set my 5th instead of the 2nd partition to be legacy_boot I get Missing OS

It's alive!

(As my old Question got deleted https://askubuntu.com/q/516730/319747)

My guess is, that I have to copy some of the *.c32 and other files
to a syslinux folder eighter on my EFI (where?!) or on my root
partition (/boot/syslinux?!) to get it to work – am I right? What
files are essential?

Further, I guess I will need that syslinucx.cfg file too – right?

My goal would be at least a direct boot of the lubuntu system on the
root ext4 partition.

Update:

Although I have no idea why, I got it working – but not with a manual
install.

the pmbr flag was bad and prohibited my UEFI system from booting the stick as UEFI

the legacy_boot flag was necessary for my 5th partition (linux root)

I had to use extlinux --install /path/to/root/parition

I had to create a syslinux.cfg in the syslinux folder under boot of my root partition

I did all of this on a second smaller stick, then tried to copy just
the syslinux folder, but had no luck – the extlinux --install seems
to be mandatory.

Anybody knows what exactly extlinux --install does? Can it be done
manually or how else could you install a newer version like 6.02
without installing it on to your system?

Got my stick working with the partitions mentioned on BIOS, UEFI and UEFI SecureBoot, hell of a ride, learned a lot, nearly killed 2TB with parted, be careful and good luck.

Best Answer

It's possible, and it's very frequently done with both external USB sticks and internal drives.

Regarding partition table types:

BIOS normally doesn't need any partition table. It is only interested in the bootstrap code part that is the first 440 bytes of your MBR. (Although there are exceptions. Some BIOS implementations actually do break if they cannot find a MBR with one of the usual partition types. Hopefully those are rare.)

The GPT partition table doesn't physically replace a MBR – it always starts at sector 1, while the MBR is in sector 0 – so it's possible for a disk to have both. In fact, most GPT disks do have a "protective MBR" containing just a single partition that covers the entire disk, to prevent older MBR-only partitioning tools from accidentally destroying the data.

So you can install, for example, the Syslinux boot sector into your MBR, and it will boot. (The syslinux-install_update script will do this for you, but you can look for gptmbr.bin in your syslinux package to do it manually.)

Much like the "active" flag on MBR partitions, Syslinux will look for the "legacy BIOS bootable" flag on GPT partitions (bit 2 – UEFI spec 2.4 section 5.3.3 table 20); the aforementioned script also sets that flag automatically if you have sgdisk (from gptfdisk) installed.

GRUB can also be used, but it's also a bit more annoying. Since GRUB 2 wants to "embed" parts of itself in the traditionally-unused sectors 1-62, it would overwrite a GPT that's stored in the same location. So you might need to create a dedicated partition of 2-4 MB and mark it as BIOS-bootable, so that grub-install would find itself an embedding place.
On the other hand, the UEFI specification does require support for MBR partition types (section 12.3.1) and assign the MBR partition type 0xEF to the EFI system partition (section 5.2.2).

So if you for some reason cannot get your disk working with GPT, you still can create an EFI system partition on MBR, and it will be used as long as it has the correct filesystem and all the necessary files (section 12.3.1.3):

For removable media devices there must be only one UEFI-compliant system partition, and that partition must contain an UEFI-defined directory in the root directory. The directory will be named EFI. All OS loaders and applications will be stored in a subdirectory below EFI called BOOT. There must only be one executable EFI image for each supported processor architecture in the BOOT directory. For removable media to be bootable under EFI, it must be built in accordance with the rules laid out in Section 3.4.1.1.

Regarding operating systems, Linux generally does not care the slightest bit about whether it's booted from BIOS today and from UEFI tomorrow. I've had to reboot my laptop from UEFI mode to "BIOS compatibility" mode and back maybe a hundred times this week, while trying to find a bug in the 3.17 UEFI support...

Note that the "BIOS to UEFI Transformation" article is about a quite different thing. It describes how to install UEFI itself – an UEFI implementation called "DUET" – to be started from a BIOS-only system. It has nothing to do with booting an operating system directly from BIOS.

Related Solutions

UEFI Legacy boot hidden – tricks to unlock it

Problem solved. A 'BIOS' update from Acer did enable the Legacy boot mode choice.

The instructions provided in the Crunchbang forum assume you can boot the installation media... And the Crunchbang developers have yet to release an EFI-bootable image. This means that I would in fact need legacy mode to install the OS and then following those instructions, make it UEFI-bootable. So you can sleep tonight, knowing I am booting my Linux through UEFI.

EFI may have started out in the 90s, but it has only recently made its way into mainstream computers/laptops. Even Hiren's bootcd hasn't yet been re-made to support it.

Linux – How to create hybrid live USB

As you request a clear illustration of how to do it, here it is. I assume you have your live Linux booted.

Partition the USB thumb drive

I recommend the command line tool gdisk. It produces very clean results. Alternatively, you can use gparted.
1. Create a new partiton table. Use GPT with a protective MBR.
2. Define these partitions:
  - (optional) A data partition
  - A Linux partition
  - A legacy BIOS boot partition (1MB is enough)
  - A EFI System partition (at least 32MB)
3. Example: On my 64GB thumb drive, the result looks like this:
```
Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048       107632639   51.3 GiB    0700  DATA
   2       107632640       124411903   8.0 GiB     8300  Linux filesystem
   3       124411904       124413951   1024.0 KiB  EF02  BIOS boot partition
   4       124413952       124822453   199.5 MiB   EF00  EFI System
```
Install Linux to the USB thumb drive using any method.

During the process, format the Linux partition with a filesystem of your choice, preferably ext4. Use this partition as root /.
Format the EFI System partition with FAT16.
The BIOS boot partition remains unformatted.
Install GRUB twice

In a final step, install GRUB for both boot methods, UEFI style booting and legacy BIOS booting.
```
grub-install --target=x86_64-efi --removable /dev/sdx

grub-install --target=i386-pc /dev/sdx
```
Where /dev/sdx is your USB thumb drive, obviously.
That --removable is important. Took me three hours to realize I need it on a removable USB thumb drive...

If you install GRUB to the thumb drive from the "outside" (not having booted the Linux from the USB thumb drive), you need to mount the Linux partition first. Maybe you mount it into /mnt. Then you mount the EFI System partition into the Linux partitions /mnt/boot/efi directory. Use --root=/mnt as parameter for grub-install. Only then grub-install finds all necessary directories.

Done.

For further reading:
We did not really define partitions in the MBR. So you may ask, why it does work on legacy BIOS machines. Keep in mind, we installed GRUB into the MBR. During the legacy BIOS boot process, the bootloader stored in the MBR is executed. This loads stage 1 of GRUB, which then proceeds to load stage 2 from the legacy BIOS boot partition. But at this time, GRUB does not actually know anything about partitions MBR or otherwise. For this reason, the information about the position of the BIOS boot partition has been embedded into GRUB stage 1. Consequently, if the BIOS boot partition is moved, you need to reinstall GRUB. After GRUB stage 2 is loaded, GRUB understands GPT and can continue with booting the Linux kernel.

Best Answer

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UEFI Legacy boot hidden – tricks to unlock it

Linux – How to create hybrid live USB

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